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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / March 2008Carburetor EGR port question
Does anyone have any idea how much vacuum should develop at an EGR port on a carburetor with the engine revved to about 2000rpm? I installed a brand spanking new Holley 2280 carburetor on my 87 Dodge Dakota V6 engine and failed the NO part of the California smog test. The HC and CO tests passed well below average. I came back home and checked the action on the EGR valve. No movement on the visible piston when the engine was revved. The EGR valve checked out okay when tested. It opened with less than 10 inches of vacuum and stayed open indefinitely. The Coolant Vacuum Switch Cold Closed (CVSCC) is operating correctly. The vacuum hoses involved are all in good shape, no leaks. I checked the vacuum at the EGR port on the brand spanking new carburetor and only got about 1 or 2 inches of vacuum at about 2000 rpm. Manifold vacuum is 19 inches at a 700rpm idle. What gives? > Does anyone have any idea how much vacuum should develop at an EGR port > on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 16 lines] > > What gives? You sure you're hooked up to the right port? A few pages of 2280 info a quick search found..... http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info.jpg http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info2.jpg http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info3.jpg http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info4.jpg >> Does anyone have any idea how much vacuum should develop at an EGR port >> on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 18 lines] > > You sure you're hooked up to the right port? I'm absolutely sure. I have a spare carb of the same design that is disassembled. There are not many who are more familiar with the guts of this carb than I am. I became knowledgeable about it through necessity. The truck came stock with a Holley 6280, which is the electronic feedback version of the 2280, the main difference being a fuel mixture control solenoid. The solenoid is no longer available as a replacement part and when it goes the only recourse is to locate a used one, which in my experience is no better than the one that went south. So I decided to replace the feedback 6280 with the non-feedback 2280. The problem with the mixture control solenoid first surfaced about eight years ago. After sleeping on it, I think the problem may be a leak in the purge line to the charcoal canister. This purge line enters the carb through a port in the exact same place as the EGR port, just above the closed throttle plates. This would explain the low vacuum at the EGR port. The lack of EGR function, plus the vacuum leak, which would cause a lean condition, would combine to create a higher than normal temperature in the combustion chamber resulting in the abnormally high NO readings. The ceramic insulators on the plugs have that very white look caused by a lean fuel mix. Soon as I finish my morning cup I'm going to warm up the engine, disconnect the purge line, plug the purge line port in the carb and test the EGR function again. > A few pages of 2280 info a quick search found..... > http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info.jpg > http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info2.jpg > http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info3.jpg > http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info4.jpg  SignatureChuck Norris can fool all of the people all of the time and Chuck Norris supports McCain. McCain -- it rhymes with Hussein, Bahrain, cocaine, insane, wolfbane, chest pain and chow mein. >>> Does anyone have any idea how much vacuum should develop at an EGR port >>> on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 47 lines] >> http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info3.jpg >> http://www.slantsix.org/articles/choke-adjust/carb-info/2280-info4.jpg Are you absolutely certain you haven't bypassed the vacuum amplifier? As I recall, venturi vacuum only generates around two inches vacuum max and thus needs the vacuum amplifier to operate the EGR valve. Again, if I recall correctly, the amplifier will boost it to around 8 inches. >>>> Does anyone have any idea how much vacuum should develop at an EGR port >>>> on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 50 lines] > needs the vacuum amplifier to operate the EGR valve. Again, if I recall > correctly, the amplifier will boost it to around 8 inches. I found the problem. There are two available ports that tap into the carb just below the closed throttle plates. One develops vacuum and the other doesn't. The one that doesn't develop vacuum is designated in the installation sheet that came packed with this new carb as the 'EGR vacuum line'. The one that does develop vacuum is designated as the 'spark vacuum line'. On this version of the 2280, the designated EGR port is tied into another port that is much higher up in the venturi via an external vacuum hose with a tee fitting, and this tee fitting is then supposed to connect to the EGR valve. However, the designated EGR port just doesn't develop sufficient vacuum as measured directly with a vacuum meter. With or without the connection to the higher port, the vacuum is the same, less than two pounds at over 2000rpm. The EGR valve begins to open at about 3 pounds and is fully opened at about 5 pounds. The port designated as the spark vacuum line *does* develop the proper vacuum to operate the EGR valve. The spark vacuum on this truck is supplied directly from the manifold vacuum. I've got the factory manual which shows this in the same vacuum hose routing diagram that is pasted to the underside of the hood. So whatever the problem is with the designated EGR port on this carb, the designated spark vacuum port has the proper vacuum characteristics to operate the EGR valve: no vacuum at idle, increasing vacuum as the throttle is opened. If I connect the EGR valve directly to the designated spark vacuum port the EGR valve responds to the throttle as it is supposed to. However, if I connect the designated spark vacuum port to the higher port via the tee fitting, the response is sluggish to non-existent. Therefore, in the interest of proper EGR operation and passing the smog test, I am chucking what's in the instructions and going with my gut on this one. > This would explain the low vacuum at the EGR port. The > lack of EGR function, plus the vacuum leak, which would cause a lean > condition, would combine to create a higher than normal temperature in > the combustion chamber resulting in the abnormally high NO readings. Not to nit pick but lean air fuel mixtures don't burn hotter. They burn slower which causes associated component temperatures to rise. Lean doesn't cause higher NOx, the extra O2 in the exhaust from a lean mixture makes the reduction bed of a 3 way catalyst less efficient resulting in higher NOx at the tail pipe. >> This would explain the low vacuum at the EGR port. The >> lack of EGR function, plus the vacuum leak, which would cause a lean [quoted text clipped - 6 lines] > exhaust from a lean mixture makes the reduction bed of a 3 way > catalyst less efficient resulting in higher NOx at the tail pipe. Nit picking appreciated! It's always valuable to learn more precisely what is going on. It makes perfect sense to me the way that you explained it. Perhaps you could enlighten me on the effect of ignition timing on emissions. I just got back from passing the smog test after initially failing it. The failure was caused by improper vacuum to the EGR valve deom the carburetor and a minor manifold vacuum leak. The vacuum being supplied to the EGR valve by the Holley 2280 carburetor was insufficient to open the EGR valve, even at over 2000rpm. This non-functioning EGR valve and the minor manifold vacuum leak caused a measurement of over 3600 PPM of NOx. Anything over 1195 PPM is a failure. Below is the failed test results. -------------------- Percent of CO2 15mph 1333rpm - 10.8 25mph 1309rpm - 10.7 -------------------- Percent of O2 15mph 1333rpm - 5.9 25mph 1309rpm - 6.0 ------------------- HC PPM 15mph 1333rpm - 34 - PASS (maximum allowable is 134) 25mph 1309rpm - 26 - PASS (maximum allowable is 106) ------------------------- Percent of CO 15mph 1333rpm - 0.01 - PASS (maximum allowable is 0.90%) 25mph 1309rpm - 0.01 - PASS (maximum allowable is 1.14%) -------------------------------------------------------- NOx PPM 15mph 1333rpm - 3641 - GROSS POLLUTER (maximum allowable is 1095) 25mph 1309rpm - 3225 - GROSS POLLUTER (maximum allowable is 1140) ----------------------------------------------------------------- After failing the test, I checked the action of the EGR valve and found the condition I described above. After correcting the condition I took the truck back and passed the test with the following results. -------------------- Percent of CO2 15mph 1333rpm - 10.4 25mph 1309rpm - 10.7 -------------------- Percent of O2 15mph 1333rpm - 6.7 25mph 1309rpm - 6.1 ------------------- HC PPM *15mph 1333rpm - 132 - PASS (maximum allowable is 134)* 25mph 1309rpm - 65 - PASS (maximum allowable is 106) ------------------------- Percent of CO 15mph 1333rpm - 0.01 - PASS (maximum allowable is 0.90%) 25mph 1309rpm - 0.04 - PASS (maximum allowable is 1.14%) -------------------------------------------------------- NOx PPM 15mph 1333rpm - 626 - PASS (maximum allowable is 1095) 25mph 1309rpm - 606 - PASS (maximum allowable is 1140) ------------------------------------------------------ I'm a bit concerned that the truck passed the 15mph test for HC by only 2 PPM. I would like to try to lower the HCs from the tailpipe. The catalytic converter is a brand new replacement. Would changing the ignition timing lower the HC reading? Or changing the air fuel ratio through either resizing the main jets or adjusting the float level? The ignition timing is currently set at 7 degrees BTDC with the vacuum line disconnected from the transducer at the computer, as per the shop manual. The carb is a new (not rebuilt) Holley 2280. It is the non-feedback version of the Holley 6280 that came stock with this 87 Dakota V6. The mixture control solenoid for the Holley 6280 is no longer available as a replacement part so I tracked down a new 2280 on eBay and bolted it on. This configuration no longer benefits from the input from the O2 sensor, but it was the best I could do on short notice. The way I see it I have three main ways to lower HCs: 1. Advance or retard the ignition timing 2. Enrich or lean out the fuel mixture by increasing or decreasing the size of the main jets in the carb. 3. Enrich or lean out the fuel mixture by raising or lowering the level of fuel in the bowl via the float setting, which is currently stock. From the test results, I have more room to increase NOx than HCs so if lowering HCs cause NOX to rise, there is some headroom there. Please feel free to nitpick away. It would go unappreciated. Jack >>> This would explain the low vacuum at the EGR port. The lack of EGR >>> function, plus the vacuum leak, which would cause a lean condition, would [quoted text clipped - 119 lines] > > Jack I don't know why your HC's went up just from fixing an inop EGR valve ? High HC is from a rich mixture. Did you also mess with the charcoal canister vent line ? I would first try to lower the HC reading by leaning out the idle mixture screws, if that doesn't work then try the float level before you try switching main jets. One other question, was the engine and converter fully warmed up before the test ? >>>> This would explain the low vacuum at the EGR port. The lack of EGR >>>> function, plus the vacuum leak, which would cause a lean condition, would [quoted text clipped - 127 lines] > One other question, was the engine and converter fully warmed up before the > test ? Hi Mike, As to the last question, yes, the engine was fully warmed up as indicated by the temp gauge. I don't know what constitutes 'fully warmed up' for the cat. The engine was fully warmed up when the smog tech drove it onto the dynamometer. He did a 15mph test and a 25mph test, during which the engine was turning at about 1340 rpm, as indicated on the test result sheet. I am somewhat mystified by that. I would expect the rpms to be higher during the 25mph test, but it was actually lower by 22 rpms. Another one of life's unexplained mysteries. The test was long enough to warm up the cat, I would guess. There may also have been a minor manifold vacuum leak. The bolts fixing the EGR valve to the intake manifold were slightly loose. If I had a manifold vacuum leak during the first test, that would have introduced a lean mix. Fixing the leak would richen up the mix. That would explain the higher HC on the second test. One bolt on the EGR was so loose that when I tried to loosen it with what appeared to my eye to be a 1/2" hex head socket, I thought I must have got it wrong as there was no resistance, so I put on a 7/16" socket and that didn't fit. I tried metric and nothing that fit on the bolt head gripped. That's when I tried my fingers and the bolt unscrewed easy as pie. Being as I am my own mechanic I felt somewhat stupid, but soon got over it, remembering that sh.t happens. So I probably had a vacuum leak. I didn't mess with the charcoal vent line except to put a hose clamp (damn, you're good) on where it connected to the carb. But to be honest, I don't think it was all that loose, but I had a couple of extra small hose clamps knocking around and figured what the hey. As far as leaning out the idle mixture screws goes, how much does the idle circuit figure in at 1350 rpm on the engine and 15 and 25 mph on the speedometer? Roger on adjusting the float level before changing the jets. I like that because it doesn't require getting new jets, just bending metal. The Holley 2280 carb that I put on this 3.9L (239 cu) engine was used on Chrysler's 318 engine. It's the same body as the Holley 6280 that came stock on the 87 Dakota, but it doesn't have the mixture control solenoid, which is no longer available as a replacement part. As this part went south on the original carb, and any rebuilt 6280 will have an old mixture control solenoid, those of us who have this carb are left to our own devices. My solution, as was that of others with the know-how, was to install a non-feedback 2280. Just so ya know... Do you have any light to shed on adjusting the timing either way, advanced or retarded, to bring down HCs? I have found arguments both ways while googling the web and the groups. Thanks for your sharing your knowledge. Jack > >>> This would explain the low vacuum at the EGR port. The lack of EGR > >>> function, plus the vacuum leak, which would cause a lean condition, would [quoted text clipped - 127 lines] > > I don't know why your HC's went up just from fixing an inop EGR valve ? Why wouldn't the HCs increase? When the exhaust gas recirculation valve opens, what is it allowing into the intake manifold/ combustion chamber? CO2, CO, O2, NOx and HC. When the exhaust gas recirculation valve opens what happens to manifold pressure? It goes up. What does the power valve do when manifold pressure goes up? It opens and allows more HC (gasoline) to flow into the venturi in the carb. >>>>> This would explain the low vacuum at the EGR port. The lack of EGR >>>>> function, plus the vacuum leak, which would cause a lean condition, would [quoted text clipped - 130 lines] > manifold/ combustion chamber? > CO2, CO, O2, NOx and HC. Yes, it is reasonable to assume that these gases would increase in the exhaust stream over their presence in a non-EGR exhaust stream, but only in proportion to the total EGR gases that are reintroduced to a fresh intake fuel mixture, 5 to 15 percent from what I have read. In my case, the HC content increased 388% at 15 mph. > When the exhaust gas recirculation valve opens what happens to > manifold pressure? > It goes up. > What does the power valve do when manifold pressure goes up? > It opens and allows more HC (gasoline) to flow into the venturi > in the carb. My source tell me you got that backwards. As manifold pressure goes up, the power valve is closed. As manifold pressure goes down, the power valve opens. My source is "Holley Carburetors and Manifolds" by Mike Urich and Bill Fisher. HPBooks, 1987: When the engine is called upon to produce power in excess of normal cruising requirements, the carburetor has to provide a richer mixture. Added fuel for power operation is supplied by the power system controlled by manifold vacuum. Manifold vacuum accurately indicates engine load. Vacuum is usually strongest at idle. As load increases, the throttle valve must be opened wider to maintain a given speed. This offers less restriction to air entering the intake manifold and reduces manifold vacuum. A vacuum passage in the carburetor applies manifold vacuum to a power-valve piston or diaphragm. At idle or normal cruising conditions, manifold vacuum acting against a spring holds the valve closed. As high power demands load the engine, manifold vacuum drops. Below a preset point, usually about 6 inches of mercury (in.Hg), the power valve spring overcomes manifold vacuum and opens the power valve. Fuel flows through the power valve and through a power-valve restriction to join fuel already flowing through the main metering system from the main jet. The mixture is richened. http://books.google.com/books?id=ClyzQHlQbjYC&pg=PA28&lpg=PA28&dq=%22When+the+en gine+is+called+upon+to+produce+power%22&source=web&ots=SdPf9kX1c4&sig=bDsxQZoaKd Sk_aQ98Kxp41-vp4k&hl=en Scroll down to the yellow hi-lited text Jack > > Why wouldn't the HCs increase? When the exhaust gas > > recirculation valve opens, what is it allowing into the intake [quoted text clipped - 6 lines] > intake fuel mixture, 5 to 15 percent from what I have read. In my case, > the HC content increased 388% at 15 mph. My reply to Mike wasn't based upon your readings, it was based upon his statement. In your case, if the engine is running lean to begin with, the addition of EGR is going to displace any burnable mixture that might have stood a chance of combusting. > > When the exhaust gas recirculation valve opens what happens to > > manifold pressure? [quoted text clipped - 4 lines] > > My source tell me you got that backwards. Nope. > As manifold pressure goes up, > the power valve is closed. As manifold -vacuum- goes -up- the power valve closes. Manifold vacuum is a great way to determine engine health, it's a lousy way to refer to how an engine and fuel system operate. Right now assuming your truck is parked and not running, the manifold pressure is high and the power valve is open. Assuming that you're somewhere below 1000 feet altitude, the pressure inside your manifold parked and engine not running is probably somewhere near 28 or 29 inches of mercury. If you were to then start the engine, the manifold pressure might drop to 10 inches of mercury. If we subtract the 10 inches of mercury running from the 29 inches of mercury measured with the engine not running, we get 19 inches which would be a fairly healthy "manifold vacuum" reading. > As manifold pressure goes down, the power > valve opens. > > My source is "Holley Carburetors and Manifolds" by Mike Urich and Bill > Fisher. HPBooks, 1987: I know the book. > When the engine is called upon to produce power in excess of normal > cruising requirements, the carburetor has to provide a richer mixture. [quoted text clipped - 20 lines] > engine+is+called+upon+to+produce+power%22&source=web&ots=SdPf9kX1c4&sig=bDsxQZ > oaKdSk_aQ98Kxp41-vp4k&hl=en Please understand, I'm not referring to manifold vacuum. >>> Why wouldn't the HCs increase? When the exhaust gas >>> recirculation valve opens, what is it allowing into the intake [quoted text clipped - 74 lines] > > Please understand, I'm not referring to manifold vacuum. Ahn... you're right. You referred to manifold pressure, not vacuum. SignatureChuck Norris can fool all of the people all of the time and Chuck Norris supports McCain. McCain -- it rhymes with Hussein, Bahrain, cocaine, insane, wolfbane, chest pain and chow mein. >> >>> This would explain the low vacuum at the EGR port. The lack of EGR >> >>> function, plus the vacuum leak, which would cause a lean condition, [quoted text clipped - 145 lines] > manifold/ combustion chamber? > CO2, CO, O2, NOx and HC. Yep, the EGR valve allows exhaust gas back into the combustion chamber, but, it is only a very small percentage of the total combution chamber volume. The exhaust gas was already burnt once in the combustion chamber, how does running it through the combustion chamber a second time cause the HC to increase even further ? Isn't the HC reading from the smog test unburned hydrocarbons ? > When the exhaust gas recirculation valve opens what happens to > manifold pressure? > It goes up. > What does the power valve do when manifold pressure goes up? > It opens and allows more HC (gasoline) to flow into the venturi > in the carb. Yep, that's how the power enrichment works as well but why such a jump in HC ? This is the first time I remember seeing a NOx problem fixed were the HC reading jumped up like that. Does this have anything to do with the vehicle being equiped with an air pump ? We don't see too many air pumps on the east coast. > > Why wouldn't the HCs increase? When the exhaust gas > > recirculation valve opens, what is it allowing into the intake [quoted text clipped - 4 lines] > but, > it is only a very small percentage of the total combution chamber volume. So? If the air fuel mixture is lean to begin with, how does adding exhaust gas make the flame propagate better? > The exhaust gas was already burnt once in the combustion chamber, how does > running > it through the combustion chamber a second time cause the HC to increase even > further ? See above. > Isn't the HC reading from the smog test unburned hydrocarbons ? Yes it is. Ever open an EGR valve at idle? Did the engine run better or worse? Do you suppose HC goes up or down if you open the EGR at idle? > > When the exhaust gas recirculation valve opens what happens to > > manifold pressure? [quoted text clipped - 6 lines] > HC ? This is the first time I remember seeing a NOx problem fixed were the > HC reading jumped up like that. Not for me. It's very common on some engines to repair a non functioning EGR for a NOx failure and have the car fail on HC. Typical 4 cylinder where the EGR feeds into the intake ports individually (4 separate EGR passages) and 2 or 3 are plugged. The 1 or 2 that do flow EGR are over fed and cause a misfire. Roto-Root the passages and everything is fine... > Does this have anything to do with the vehicle > being equiped with an air pump ? The high HC? Maybe yes, maybe no. That's why there's a thing called 'diagnostics.' I'd watch the reading with the air pump disabled. The OP has a 21 year old truck, what are the odds hat the air pump is original? I couldn't get the air pump on my bought new 85 F-150 to last more than three years. Air pumps tend to have a generic universal design, what if instead of a 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement pump made for a 7.4 liter engine. You -can- pump too much air into a catalytic converter and snuff out the fire. > We don't see too many air pumps on the east > coast. Dunno why, they were pretty common in the day that the OPs truck was built. Now they're likely to be electric. >> > Why wouldn't the HCs increase? When the exhaust gas >> > recirculation valve opens, what is it allowing into the intake [quoted text clipped - 20 lines] > Yes it is. > Ever open an EGR valve at idle? Yep. > Did the engine run better or worse? Didn't run at all, they don't run well on an inert gas. > Do you suppose HC goes up or down if you open the EGR at idle? Being the engine wouldn't stay running I would say it went down. ;) If it would stay running it would have a lean misfire that would lead to an increase in HC. >> > When the exhaust gas recirculation valve opens what happens to >> > manifold pressure? >> > It goes up. >> > What does the power valve do when manifold pressure goes up? >> > It opens and allows more HC (gasoline) to flow into the venturi >> > in the carb >> Yep, that's how the power enrichment works as well but why such a jump >> in [quoted text clipped - 13 lines] > The high HC? Maybe yes, maybe no. That's why there's a thing called > 'diagnostics.' I'd watch the reading with the air pump disabled. Yes, I'd like to see the results with the air pump disabled. > The OP has a 21 year old truck, what are the odds hat the air pump is > original? I couldn't get the air pump on my bought new 85 F-150 to last [quoted text clipped - 4 lines] > You -can- pump too much air into a catalytic converter and snuff out the > fire. Yep, I see your point here. My experience has been that aftermarket emission parts are junk. >> We don't see too many air pumps on the east >> coast. > > Dunno why, they were pretty common in the day that the OPs truck was > built. They sure were, but living in the rust belt they don't last very long and are long ago rusted away. > Now they're likely to be electric. > > Yes it is. > > Ever open an EGR valve at idle? [quoted text clipped - 4 lines] > > Didn't run at all, they don't run well on an inert gas. Next time, don't open it so far. Try a 10% or 20% command on your scn tool instead of 80% . > > Do you suppose HC goes up or down if you open the EGR at idle? > [quoted text clipped - 3 lines] > increase > in HC. No, it wouldn't be a lean misfire. Lean misfire comes from too much air and not enough fuel. Opening the EGR does not add more air. The exhaust gasses displace what would have been combustible mixture in the combustion chamber, the actual ratio of that combustible mixture doesn't change. If you have an engine with a leaking EGR valve at idle, fattening up the mixture doesn't improve how the engine will idle. Comparing secondary spark lines on a ignition scope, a lean mixture looks completely different than a stuck open or leaking EGR valve. > > Air pumps tend to have a generic universal design, what if instead of a > > 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement [quoted text clipped - 4 lines] > Yep, I see your point here. My experience has been that aftermarket > emission parts are junk. Yup. > > > Yes it is. > > > Ever open an EGR valve at idle? [quoted text clipped - 18 lines] > No, it wouldn't be a lean misfire. Lean misfire comes from too much air > and not enough fuel. Opening the EGR does not add more air. It does add gas which displaces air. That would mean less air going into the cylinders. At least that is what would happen in the first fractions of a second. So for a very brief period of time you get a rich condition. > The exhaust gasses displace what would have been combustible mixture in > the combustion chamber, the actual ratio of that combustible mixture > doesn't change. How can the mixture not change if you just took away some of the air. Of course in about the time it takes you to blink the dynamic system that controls fuel, air, timing and idle speed is going to react to those changes - so any conclusions you draw from this experiment are more than likely to be completely wrong. -jim > If you have an engine with a leaking EGR valve at idle, fattening up the > mixture doesn't improve how the engine will idle. > Comparing secondary spark lines on a ignition scope, a lean mixture > looks completely different than a stuck open or leaking EGR valve. > > > Air pumps tend to have a generic universal design, what if instead of a > > > 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement [quoted text clipped - 6 lines] > > Yup. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > > No, it wouldn't be a lean misfire. Lean misfire comes from too much air > > and not enough fuel. Opening the EGR does not add more air. > > It does add gas which displaces air. Displaces air -and- fuel. > That would mean less air going into > the cylinders. Less air -and- fuel going into the cylinder. > At least that is what would happen in the first fractions > of a second. So for a very brief period of time you get a rich condition. [quoted text clipped - 4 lines] > > How can the mixture not change if you just took away some of the air. What makes you think that EGR only takes away air. What makes you think that EGR takes away anything? EGR displaces a volume in a cylinder. > Of > course in about the time it takes you to blink the dynamic system that > controls fuel, air, timing and idle speed is going to react to those > changes - so any conclusions you draw from this experiment are more than > likely to be completely wrong. None of what I've said are mine nor are they conclusions. IOWs, you assume wrong again They are the physics of the internal combustion engine, documented and published (but probably not in Popular Mechanics). Don't take my word for it, feel free to run Simpson's non operating EGR valve gas readings and his operating EGR valve gas readings thru a Lambda calculator. You'll find that the air fuel ratio changes by .01 which is well within the expected sampling error of the type of equipment being used for his tests. > > > No, it wouldn't be a lean misfire. Lean misfire comes from too much air > > > and not enough fuel. Opening the EGR does not add more air. > > > > It does add gas which displaces air. > > Displaces air -and- fuel. One can only guess what it is you are talking about. Let's assume you were talking about a modern car with fuel injection. Air gets displaced meaning less will enter intake (at least for an instant). The fuel at the same time doesn't get displaced. There is nothing physical to cause the fuel to be displaced. If the end result is less fuel is delivered it is only because the engine's control system delivers less fuel (but it could deliver more air or both). On a vehicle with carb it's different because airflow is part of the physical process that delivers fuel. But that still doesn't mean the air/fuel ratio will stay the same without some engineering effort to make that happen. > > That would mean less air going into > > the cylinders. > > Less air -and- fuel going into the cylinder. Maybe or maybe not. All depends how a particular system is designed. Hopefully it's designed well enough that it won't change the air/fuel ratio very much in your scenario since EGR failures are not rare occurrences. > > At least that is what would happen in the first fractions > > of a second. So for a very brief period of time you get a rich condition. [quoted text clipped - 8 lines] > What makes you think that EGR takes away anything? > EGR displaces a volume in a cylinder. That was your terminology. Air is a gas. So is the exhaust coming from EGR - fuel is not. If you say some of the volume of gas is displaced that equivalent to saying some is taken away. > > Of > > course in about the time it takes you to blink the dynamic system that [quoted text clipped - 3 lines] > > None of what I've said are mine nor are they conclusions. It sounded like it was your experiment. It also sounded like your conclusion or at least you hoped others would reach from the experiment. The only reason your experiment would lead to that erroneous conclusion is because that is the way it is engineered to work. If the controls are working as they should then it won't affect air/fuel because it is designed not to. > IOWs, you assume wrong again > They are the physics of the internal combustion engine, documented and [quoted text clipped - 6 lines] > the expected sampling error of the type of equipment being used for his > tests. I suspect that Chrysler had a good bit of data on the vacuum controls for EGR in the 80's also. And that data is what they used to design EGR controls so that didn't throw the air/fuel ratio out of wack. But when you start doing your own design on an engine as the OP is doing it is extremely unlikely that you will end up not changing air/fuel ratio if you just slap any EGR control onto the system any which way and simply hope. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> > > No, it wouldn't be a lean misfire. Lean misfire comes from too >> > > much air and not enough fuel. Opening the EGR does not add more [quoted text clipped - 9 lines] > The fuel at the same time doesn't get displaced. There is nothing > physical to cause the fuel to be displaced. I'd think the engine's computer would sense the decrease in fresh air intake and reduce fuel delivery accordingly. SignatureTegger >>>> Why wouldn't the HCs increase? When the exhaust gas >>>> recirculation valve opens, what is it allowing into the intake [quoted text clipped - 57 lines] >> original? I couldn't get the air pump on my bought new 85 F-150 to last >> more than three years. The air pump is original equipment. I bought the truck new and I have done all my own work on it, including changing the lifters and changing a blown head gasket, two separate operations. So I know the air pump is original. Whether it's working as it should today, I can't say. I tested it a few years ago according to the manual and it seemed to be working then. What has me puzzled at this point is which of the 4 operations I performed on the fuel and ignition systems contributed to the skyrocketing of CO emissions on the third test (test results reprinted below). HC and NO came down significantly, as did O2, but at the expense of CO. Only the enrichening of the idle mixture and the widening of the canister purge line ports in the wall of the carb throttle body could have fattened up the mix, which would have resulted in the higher CO and lower O2 readings. Assuming no freakishly timed breakdown of the air pump, it's operation would have been the same for all 3 tests, whether working or not. If the guy who owns the smog shop will allow it, I would like to run another pre-test and see if clamping down the canister purge hose changes the readings mid-test. I leaned out the idle mixture screws just a bit after the third test. They were pretty close to lean best idle as it was. I can't imagine that the small change that I made to the idle mix could have such a strong affect on the emissions with the engine running at 1325 rpms. So the enlarging of the canister purge line ports into the venturi just above the throttle plates is the likely suspect, IMO. %CO2 %O2 HC PPM %CO NOx PPM 15mph 1st test 10.8 5.9 34 .01 3641-FAIL 2nd test 10.4 6.7 132* .01 626 3rd test 12.2 3.6 82 1.02-FAIL 358 25mph 1st test 10.7 6.0 26 .01 3225-FAIL 2nd test 10.7 6.1 65 .04 606 3rd test 12.5 2.9 73 1.14** 191 1st test - 1. EGR run from EGR port on carb resulting in essentially no EGR function 2. MSD ignition hooked up 2nd test - 1. EGR run from spark advance port on carb 2. MSD ignition not hooked up 3rd test - 1. EGR run from modified EGR port on carb 2. Idle mixture enriched slightly 3. The ports entering both barrels from the canister purge hose were enlarged to correspond to those in the original stock carb. 4. MSD ignition hooked up * passing is 134, measured 132 ** passing is 1.14, measured 1.14 >> Air pumps tend to have a generic universal design, what if instead of a >> 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement [quoted text clipped - 14 lines] > >> Now they're likely to be electric. > >> This would explain the low vacuum at the EGR port. The > >> lack of EGR function, plus the vacuum leak, which would cause a lean [quoted text clipped - 119 lines] > > Jack Hi Jack, Does this truck have an air pump? The reason I ask is because there is an awful lot of O2 in the exhaust sample. If the truck has an air pump, that would account for it, but unfortunately the dilution from the air pump makes analyzing the gas samples difficult. If there is NO air pump, here;s what I think; too much O2, too much HC, not enough CO2 and not enough CO. That is a lean mixture. Richening it up a bit will drop the HCs, lower the O2 and increase the CO2. A richer mixture doesn't contribute to more NOx typically as long as the other NOx treatments are functioning as they should. Advancing ignition timing hurts NOx, it tends to hurt HC and CO also, the exception being if the ignition system is marginal and HCs are caused by an ignition misfire, this is because it takes less voltage to ionize the plug gap the farther the piston is away from TDC (advanced). Late ignition timing tends to help HC and CO for the exact reasons given in my first post, hotter combustion chamber wall, hotter exhaust valve and port, but late timing can reveal marginal ignition components. CO2 is the best indicator of combustion efficiency, higher is better so anything you do that raises CO2 shows you're headed in the right direction. I mention this because your CO2 reading are low, by about 3 percent or more. An efficient catalytic converter lowers CO and HC and raises CO2 by its very nature, OEM catalysts are usually 90%+ efficient, aftermarket catalysts are usually only 40%-50% efficient. The only way to tell if the tailpipe readings are due to an inefficient catalyst is to take pre-cat and post cat gas samples and calculate the efficiency. Without an air pump diluting the sample a stoichiometric air/fuel ratio would read .5% CO and .5% O2 give or take .1% either way. >>>> This would explain the low vacuum at the EGR port. The >>>> lack of EGR function, plus the vacuum leak, which would cause a lean [quoted text clipped - 121 lines] > Hi Jack, > Does this truck have an air pump? Yes it does. It injects air directly into the cat. > The reason I ask is because > there is an awful lot of O2 in the exhaust sample. That's what I thought. > If the truck has an air pump, that would account for it, but > unfortunately the dilution from the air pump makes analyzing the [quoted text clipped - 3 lines] > mixture. Richening it up a bit will drop the HCs, lower the O2 > and increase the CO2. I'm confused. If there is excess O2 and excess HC, what prevents them from combining in a burn to produce more CO2? > A richer mixture doesn't contribute to more > NOx typically as long as the other NOx treatments are functioning > as they should. That's seems to be in line what what I have read concerning the formation of NOx, which is mainly a factor of a too hot combustion chamber. > Advancing ignition timing hurts NOx, it tends to hurt HC and CO > also, the exception being if the ignition system is marginal and > HCs are caused by an ignition misfire, this is because it takes > less voltage to ionize the plug gap the farther the piston is > away from TDC (advanced). I can't quite follow you on this. Did you mean that "it takes *more* voltage to ionize the plug gap the farther the piston is away from TDC (advanced)."? > Late ignition timing tends to help HC > and CO for the exact reasons given in my first post, hotter > combustion chamber wall, hotter exhaust valve and port, but late > timing can reveal marginal ignition components. Plugs, cap and rotor are all very healthy looking, but the resistance of the wires all measure below the lower spec for resistance in the shop manual. 250 ohms per inch is the minimum spec. Mine are at about 200. At this point, I should probably mention that I have an MSD Blaster Ignition, model PN 5900, installed: http://www.msdignition.com/ignition_1_5900.htm More precisely, it was installed when the truck failed the test and not installed when it passed, but I don't think it had anything to do with the failure. The non-functioning EGR system definitely played the major role, IMO. I unconnected the MSD unit for the retest because I thought that perhaps the more powerful and longer duration spark it supplied might be contributing to the hot combustion chamber conditions that caused the high NOx reading. > CO2 is the best indicator of combustion efficiency, higher is > better so anything you do that raises CO2 shows you're headed in [quoted text clipped - 10 lines] > Without an air pump diluting the sample a stoichiometric air/fuel > ratio would read .5% CO and .5% O2 give or take .1% either way. So the truck has an air pump, and given what we have hashed through here so far, I feel that, just to be sure, I should replace the plugs, wires, cap and rotor before concerning myself with the jets or the float level, even if I think they are in good shape. BTW, do you happen to know if plug wires can *lose* resistance over time? I hope all is well in your part of the world. Jack > > Hi Jack, > > Does this truck have an air pump? > > Yes it does. It injects air directly into the cat. I suspected so. The only way to make meaningful determination of the gas readings is to take the gas readings again with the air pump disabled. > > The reason I ask is because > > there is an awful lot of O2 in the exhaust sample. > > That's what I thought. At this point, it's nether good or bad until you attempt to use the gas readings as a diagnostic aid. There's a thing called the Brettschneider equation which allows with the input of 4 or 5 gas reading to accurately calculate the air fuel ratio. The equation works whether or not there is a catalytic converter ahead of where the sample is taken. What the Brettschneider equation can not compensate for however is false air introduced either by leaks in the exhaust pipes or joints or an auxiliary air system such as is on your truck. > > If the truck has an air pump, that would account for it, but > > unfortunately the dilution from the air pump makes analyzing the [quoted text clipped - 6 lines] > I'm confused. If there is excess O2 and excess HC, what prevents them > from combining in a burn to produce more CO2? Low catalytic converter efficiency. The excess gases are in the wrong ratio. Ever use a cutting torch? If you set the flame as oxidizing, you won't get the results you need. If you set the flame as carburizing, you won't get the results you need. One size fits all replacement parts... I've seen vehicles fail emissions tests because the air pump was too small, I've seen vehicles fail emissions test because the air pump was too big. (the OEMs rate/size them by CFM) > > A richer mixture doesn't contribute to more > > NOx typically as long as the other NOx treatments are functioning [quoted text clipped - 12 lines] > voltage to ionize the plug gap the farther the piston is away from TDC > (advanced)."? No, opposite that. If you have a weak ignition system, chances are it will present itself or be more problematic with less ignition advance. if I see low firing voltage on a secondary waveform on a scope and no indication of plug fouling, I first grab my timing light and check ignition timing. You can search for my posts in either of the Chevy truck groups, you want to focus on exchanges between myself and a poster named "snoman" for my attempts to get him to understand why his truck runs better with the ignition timing jacked sky high contrary to the hundreds of identical trucks I've worked on in the last 20 years that would just ping, rattle and set ESC codes when set the same or similar. > > Late ignition timing tends to help HC > > and CO for the exact reasons given in my first post, hotter [quoted text clipped - 4 lines] > the wires all measure below the lower spec for resistance in the shop > manual. 250 ohms per inch is the minimum spec. Mine are at about 200. Which shop manual specifies ohms per inch? > At this point, I should probably mention that I have an MSD Blaster > Ignition, model PN 5900, installed: [quoted text clipped - 8 lines] > might be contributing to the hot combustion chamber conditions that > caused the high NOx reading. Again, hot combustion chambers do not contribute to NOx formation. Hotter combustion does contribute to NOx formation. Hottest combustion typically occurs if the mixture is 2 percent richer than stoichiometric. > > Without an air pump diluting the sample a stoichiometric air/fuel > > ratio would read .5% CO and .5% O2 give or take .1% either way. [quoted text clipped - 3 lines] > cap and rotor before concerning myself with the jets or the float level, > even if I think they are in good shape. It's cheap enough to do on that engine. My hunch however is that the carb is a little lean. > BTW, do you happen to know if plug wires can *lose* resistance over time? Outside of leaking insulation, I can't say I've ever seen it in 37 years in the trade. The typical failure that would account for high HCs would be an open plug wire. > I hope all is well in your part of the world. Ask me again tomorrow 8-) they're forecasting 8-14 inches of snow for our area. We've already had over 100 inches this season though most of it had melted in the last two weeks. Good wrenching and let us know the results. >>> Hi Jack, >>> Does this truck have an air pump? [quoted text clipped - 79 lines] > > Which shop manual specifies ohms per inch? Page 8D-10 of the Chrysler Motors 1987 Shop Manual 2WD and 4WD Pickups Dakota Trucks Like the one shown here: http://cgi.ebay.com/ebaymotors/1987-DAKOTA-TRUCK-SERVICE-SHOP-MANUAL-2-4-WHEEL-D RIVE_W0QQitemZ260210411809QQcmdZViewItem?hash=item260210411809&_trksid=p3756.m20 .l1116 From the manual: CABLE RESISTANCE CHART Minimum---------------------Maximum 250 Ohms Per Inch 600 Ohms Per Inch > >> At this point, I should probably mention that I have an MSD Blaster [quoted text clipped - 14 lines] > Hottest combustion typically occurs if the mixture is 2 percent > richer than stoichiometric. Right... I went and re-read what you wrote about it in your first post. >>> Without an air pump diluting the sample a stoichiometric air/fuel >>> ratio would read .5% CO and .5% O2 give or take .1% either way. [quoted text clipped - 5 lines] > It's cheap enough to do on that engine. > My hunch however is that the carb is a little lean. I feel certain that the reasoning for this must be in one of your past posts. It appears counterintuitive at first glance, though... a richer mix to lower HCs at the tailpipe. Would you suggest bigger main jets or a higher float? Mike suggested leaning out the idle mixture screws to get lower HCs. At this point I am a bit more knowledgeable, but not quite sure what to do with it. What I need is tailpipe emissions wand like the one at the shop so i can monitor the changes that take place for a given tweak. > >> BTW, do you happen to know if plug wires can *lose* resistance over time? [quoted text clipped - 10 lines] > > Good wrenching and let us know the results. Will do, and thanks for all the input. > From the manual: > > CABLE RESISTANCE CHART > > Minimum---------------------Maximum > 250 Ohms Per Inch 600 Ohms Per Inch Okay, if Chrysler says so. > > Again, hot combustion chambers do not contribute to NOx formation. > > Hotter combustion does contribute to NOx formation. [quoted text clipped - 16 lines] > posts. It appears counterintuitive at first glance, though... a richer > mix to lower HCs at the tailpipe. When a cylinder gets lean enough it begins to misfire and HC goes up. The whole thing is a teeter totter balancing act. > Would you suggest bigger main jets or a higher float? I'd play with the main jets. A higher float can cause other not so desirable results. (like dripping upon shut down) > Mike suggested leaning out the idle mixture screws to get lower HCs. Both of you should look at the chart on the first page of this PDF http://www.autoshop101.com/forms/h56.pdf See what I mean about teeter totter? Which side of the bold black line is your high HC on? Then look at the chart on page 2, pay attention to where O2 and CO converge at stoichiometric, like I said earlier, .5% give or take tenth. Mike is certain that your high HC is because the mix is rich, based upon -what- I have no idea since your gas numbers are skewed by the false air from the air pump. I'm saying that I "suspect" that it's actually too lean, maybe in part because I thought you had mentioned that the plugs were white. > At this point I am a bit more knowledgeable, but not quite sure what to > do with it. What I need is tailpipe emissions wand like the one at the > shop so i can monitor the changes that take place for a given tweak. http://www.autologicco.com/AllProducts/GasAnalyzer.shtm#GasPortabl e (sorry about the line wrap) This is (IMHO) the best deal out there. >> From the manual: >> [quoted text clipped - 25 lines] > When a cylinder gets lean enough it begins to misfire and HC goes > up. The whole thing is a teeter totter balancing act. I just got back from modding the carb. See my last reply to Mike. While I had the carb off, I removed the limiter caps and will try readjusting the idle mixture screws as I have a rough idle. Apparently, this truck has always idled rough, from what I hear and read. The HCs on the successful test at 15mph test are double those at 25mph test - 132 to 65. The engine rpms for both tests reads virtually the same, though, which is a mystery. But that mystery aside, I would guess that the idle circuit plays more of a part in the fuel mixture at 15mph than at 25mph and this transmission will go all day in third gear at 15 mph. Anyway, what I guess I'm trying to say is that I will try riching up the idle circuit first. Being as it would cost me up to 30 bucks for a dry run on the dynamometer, I want to try everything that I can to get the ideal adjustments lined for a try. > >> Would you suggest bigger main jets or a higher float? > > I'd play with the main jets. A higher float can cause other not > so desirable results. (like dripping upon shut down) I have some smaller jets from the old carb that worked in conjunction with the mixture control solenoid. I hear that it's not always a good idea to drill out jets because the shape of the jets is important to the flow of the fuel, but is it always a bad idea? I guess I should mention again that the carb that I put on this 3.9L (239 cu) V6 was designed for a 318 from the early seventies. It probably was designed for a Lean Burn system as it had a throttle position sensor on it, which I took off, as this 87 Dakota is not a Lean Burn system, I don't think. Anyway, there was no throttle position sensor on the original carb, so off it came from the new one. In any case, this 2280 Holley that was used on the 318 V8 is the same body and capacity as the 6280 that came original on the 239 V6, so I am assuming that it can be tweaked to run the 239 just fine. > >> Mike suggested leaning out the idle mixture screws to get lower HCs. > > Both of you should look at the chart on the first page of this PDF > > http://www.autoshop101.com/forms/h56.pdf Wow, love it! Thanks for posting that! > See what I mean about teeter totter? > > Which side of the bold black line is your high HC on? The 15mph test, 132 PPM, is on the left, but the HC line on the graph does not come down to 65 PPM, which was the result of the 25mph test. > Then look at the chart on page 2, pay attention to where O2 and > CO converge at stoichiometric, like I said earlier, .5% give or [quoted text clipped - 6 lines] > part because I thought you had mentioned that the plugs were > white. I will pay this the attention it deserves after I get back from a test drive, or maybe tomorrow morning after a big mug of tea > >> At this point I am a bit more knowledgeable, but not quite sure what to [quoted text clipped - 4 lines] > e > (sorry about the line wrap) Not a problem. > This is (IMHO) the best deal out there. Yeow! Prices are on the high side for shade tree mechanic. > I just got back from modding the carb. See my last reply to Mike. > [quoted text clipped - 21 lines] > idea to drill out jets because the shape of the jets is important to the > flow of the fuel, but is it always a bad idea? Ya gotta do what ya gotta do. Last fall had a guy bring me one of those kit cars that's a replica of a 20s something Mercedes Benz, the drive train is 78 or 79 Mustang V-6 with a 2 barrel Motorcraft carb. All stock engine wise, all emissions equipment present and functioning. The car couldn't pass the state IM-240 test. The only thing non-stock emissions related was the exhaust, he had one of those small universal catalytic converters on it. The original Mustangs had a 3 cat system. Thing is way rich, CO is sky high. No way to fit two more cats on it. Shoot the moon, pull the carb top off, remove the jets, solder 'em shut and re-drill them .008" smaller. Why .008"? That was the next smallest drill size in my number drill set. Re-assemble and took it to the test station 2 miles away. The car fast passed which means it's running significantly cleaner then it was before. Is soldering and drilling a set of jets a kludge repair? Absolutely! Did it fix the car? Hell yes. It passed the emissions test and he called back 2 days later and said the car had never ran so good. > I guess I should mention again that the carb that I put on this 3.9L > (239 cu) V6 was designed for a 318 from the early seventies. It probably > was designed for a Lean Burn system as it had a throttle position sensor > on it, which I took off, as this 87 Dakota is not a Lean Burn system, I > don't think. Anyway, there was no throttle position sensor on the > original carb, so off it came from the new one. So, a lean jetted carb is high on HC. > In any case, this 2280 Holley that was used on the 318 V8 is the same > body and capacity as the 6280 that came original on the 239 V6, so I am [quoted text clipped - 14 lines] > > The 15mph test, 132 PPM, is on the left, How do you know that? Maybe your HC reading is to the right of the bold black line. The HC graph represented on that chart is "U" shaped isn't it? High rich of stoichiometric, drops near stoichiometric and rises again lean of stoichiometric. > but the HC line on the graph > does not come down to 65 PPM, which was the result of the 25mph test. Your test sample was taken after the catalytic converter. so naturally the numbers would be lower. The specific number aren't what I was pointing out, it's the relationships of the different gasses at different air fuel ratios, i.e., is the HC high because it's too rich or because it's too lean. Some here seem to think that HC can only be high due to a too rich fuel mixture. The only way to know which side of stoichiometric your HC numbers represent is to know what the actual unadulterated O2 measurement is. > > Then look at the chart on page 2, pay attention to where O2 and > > CO converge at stoichiometric, like I said earlier, .5% give or [quoted text clipped - 24 lines] > > Yeow! Prices are on the high side for shade tree mechanic. >> I just got back from modding the carb. See my last reply to Mike. >> [quoted text clipped - 78 lines] > relationships of the different gasses at different air fuel ratios, > i.e., is the HC high because it's too rich or because it's too lean. Got it! Using that way of looking at the graph, especially for CO, CO2 and O2, which are expressed in percentages, I can easily see that my passing test was on the lean side, the CO being a dead giveaway. > Some here seem to think that HC can only be high due to a too rich fuel > mixture. The only way to know which side of stoichiometric your HC [quoted text clipped - 4 lines] >>> CO converge at stoichiometric, like I said earlier, .5% give or >>> take tenth. Okay, now I see why you place so much store in the O2 reading. I need to richen up the mix a bit. The only tool I have at my disposal to judge The mix is the color of the ceramic insulators on the plugs and they have been pure white of late. Is plug insulator color a good indicator of proper fuel mix? That's all I have for now. If it's a good indicator, when I get a good color I will take it to the smog shop for a dry run. >>> Mike is certain that your high HC is because the mix is rich, >>> based upon -what- I have no idea since your gas numbers are [quoted text clipped - 16 lines] >>> This is (IMHO) the best deal out there. >> Yeow! Prices are on the high side for shade tree mechanic. > Okay, now I see why you place so much store in the O2 reading. I need to > richen up the mix a bit. The only tool I have at my disposal to judge [quoted text clipped - 4 lines] > I have for now. If it's a good indicator, when I get a good color I will > take it to the smog shop for a dry run. Your issue may be timing. The vehicle is designed to run with EGR. It sounds like your engine performs well without it (ignoring NOX) and with EGR it does not do as well (other than NOX). That suggests you may be able to advance the timing a degree or 2. Doing that will probably increase NOX a little but may bring the other readings back in line. -jim > >>> Mike is certain that your high HC is because the mix is rich, > >>> based upon -what- I have no idea since your gas numbers are [quoted text clipped - 15 lines] > >>> This is (IMHO) the best deal out there. > >> Yeow! Prices are on the high side for shade tree mechanic. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> Okay, now I see why you place so much store in the O2 reading. I need to >> richen up the mix a bit. The only tool I have at my disposal to judge [quoted text clipped - 10 lines] > to advance the timing a degree or 2. Doing that will probably increase NOX > a little but may bring the other readings back in line. Considering that in the last test from the smog shop (posted as my last reply to aarcuda69062) about an hour ago showed the NOx well below average, I have room to spare on that measurement. I will try your suggestion of advancing the timing two degrees and leaning out the idle mixture a bit and get another reading, but not today. > -jim > [quoted text clipped - 21 lines] > http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups > ---= - Total Privacy via Encryption =--- > > Your test sample was taken after the catalytic converter. so naturally > > the numbers would be lower. [quoted text clipped - 5 lines] > and O2, which are expressed in percentages, I can easily see that my > passing test was on the lean side, the CO being a dead giveaway. Atta boy! > >>> Then look at the chart on page 2, pay attention to where O2 and > >>> CO converge at stoichiometric, like I said earlier, .5% give or [quoted text clipped - 8 lines] > I have for now. If it's a good indicator, when I get a good color I will > take it to the smog shop for a dry run. Plug color is a method, it's naturally not going to be as accurate as a gas analyzer. Hell, it worked for Smokey Yunik for years. Below are the results of three different emissions tests on my 1987 Dodge Dakota V6 with a non-stock, non-feedback carburetor, and the differences in the emissions configuration for each test. The third test brought down HCs considerably for the 15mph test, which was my aim. However, CO measurement skyrocketed and failed at 15mph and barely passed at 25mph. O2 measurements came down by about half for both speeds and CO2 was up 17% in both tests. The difference in EGR function between using the spark vaccuum port and the modified EGR port was measured using a vacuum meter teed into the EGR vacuum line just before the EGR diaphragm. The spark vacuum port responded more strongly to the throttle and was higher at steady speeds from 15 mph through freeway speeds than the modified EGR port. However, the modified EGR port presented what appeared to me to be favorable EGR vacuum characteristics so I used that port in the third test. I am not sure which of the three modifications that I made (listed below under '3rd test') contributed to the changes in measurement of the various emissions gases, but I think it is safe to assume that I should lean out the idle mixture to bring down CO. From the looks of the CO line on this graph: http://www.autoshop101.com/forms/h56.pdf I should not have to lean it out much as that line is very steep. I would guess that between 1/4 and 1/2 half turn of each screw would do it. I set the idle mixture by the conventional method of starting with each screw 2 full turns out from fully closed and then screwing each on in until the engine starts to stumble and then backing out 1/2 turn. I backed out each screw from there about another half turn. So 1/4 to 1/2 turn in should do it. I may get another reading after that and then try what jim suggested and advance the timing 2 degrees to see how that changes the readings. That's all for now. I have to go earn some money to pay for all these tests. 30 bucks a pop for a pre-test. Not bad. Best displayed with Courier, or some other monospace font: %CO2 %O2 HC PPM %CO NOx PPM 15mph 1st test 10.8 5.9 34 .01 3641-FAIL 2nd test 10.4 6.7 132* .01 626 3rd test 12.2 3.6 82 1.02-FAIL 358 25mph 1st test 10.7 6.0 26 .01 3225-FAIL 2nd test 10.7 6.1 65 .04 606 3rd test 12.5 2.9 73 1.14** 191 1st test - EGR run from EGR port on carb resulting in essentially no EGR function 2nd test - EGR run from spark advance port on carb 3rd test - 1. EGR run from modified EGR port on carb 2. Idle mixture enriched. 3. The ports entering both barrels from the canister purge hose were enlarged to correspond to those in the original stock carb. * passing is 134, measured 132 ** passing is 1.14, measured 1.14 File under 'forgot to note': For the 3rd test, I reconnected the MSD Blaster Ignition. It was present on the 1st and 3rd tests, but not on the 2nd. http://www.msdignition.com/ignition_1_5900.htm > Below are the results of three different emissions tests on my 1987 > Dodge Dakota V6 with a non-stock, non-feedback carburetor, and the [quoted text clipped - 58 lines] > * passing is 134, measured 132 > ** passing is 1.14, measured 1.14 SignatureChuck Norris can fool all of the people all of the time and Chuck Norris supports McCain. McCain -- it rhymes with Hussein, Bahrain, cocaine, insane, wolfbane, chest pain and chow mein. >>> Your test sample was taken after the catalytic converter. so naturally >>> the numbers would be lower. [quoted text clipped - 21 lines] > Plug color is a method, it's naturally not going to be as accurate as a > gas analyzer. Hell, it worked for Smokey Yunik for years. As long as you do the run/ chop the throttle/ and shut down a plug reading is pretty good. The problem is that you don't want it to idle much if you want a good reading. Now if you really want to play with it at idle a gas analyzer works. So does a set of color tune plugs. But on an installed engine where you can't see the plugs real well they are no fun to use. But they do show how well the manifold actually spreads the mix around, or not in the case of some engines. SignatureSteve W. > When a cylinder gets lean enough it begins to misfire and HC goes > up. The whole thing is a teeter totter balancing act. I have had that happen to mine once. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: http://mikeromainjeeptrips.shutterfly.com Simpson wrote:. > The way I see it I have three main ways to lower HCs: One more way, a fresh oil change using conventional oil. High HC's can come from oil getting past the rings also so a really thin oil or old oil that goes 'thin' can bump them up. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: http://mikeromainjeeptrips.shutterfly.com > Simpson wrote:. >> The way I see it I have three main ways to lower HCs: [quoted text clipped - 3 lines] > High HC's can come from oil getting past the rings also so a really thin > oil or old oil that goes 'thin' can bump them up. Oil is fresh and the rings seem to be in good shape. I can go all the way between oil changes at 3,000 miles without having to add a quart. I bought it new and changed oil and filter fairly regularly. > Mike > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 > 'New' frame in the works for '08. Some Canadian Bush Trip and Build > Photos: http://mikeromainjeeptrips.shutterfly.com >> Simpson wrote:. >>> The way I see it I have three main ways to lower HCs: [quoted text clipped - 7 lines] > way between oil changes at 3,000 miles without having to add a quart. I > bought it new and changed oil and filter fairly regularly. Mine has read high HC's with a lean miss on mine once. >> Mike >> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 >> 'New' frame in the works for '08. Some Canadian Bush Trip and Build >> Photos: http://mikeromainjeeptrips.shutterfly.com really lean conditions don't burn hotter please explain why melted holes in pistons don't result from leaned out fuel mixtures????? > > This would explain the low vacuum at the EGR port. The > > lack of EGR function, plus the vacuum leak, which would cause a lean [quoted text clipped - 6 lines] > exhaust from a lean mixture makes the reduction bed of a 3 way > catalyst less efficient resulting in higher NOx at the tail pipe. > really lean conditions don't burn hotter > please explain why melted holes in pistons don't result from leaned out > fuel mixtures????? The explanation is in the post you're responding to. > > > This would explain the low vacuum at the EGR port. The > > > lack of EGR function, plus the vacuum leak, which would cause a lean [quoted text clipped - 6 lines] > > exhaust from a lean mixture makes the reduction bed of a 3 way > > catalyst less efficient resulting in higher NOx at the tail pipe. > Does anyone have any idea how much vacuum should develop at an EGR port > on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 16 lines] > > What gives? I don't know that particular carb, but have seen that kind of failure before. When I saw it it was a gasket in wrong or the wrong one in so a notch in the base plate was covered when it was supposed to be open. The other times I have seen the base plate in upside down. There are notches in some that need to be on the carb side, not the manifold side and if folks don't know this, the plate can be in wrong. I would figure the port you are using was blocked or it would have one or the other types of vacuum. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: http://mikeromainjeeptrips.shutterfly.com >> Does anyone have any idea how much vacuum should develop at an EGR port >> on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 24 lines] > notches in some that need to be on the carb side, not the manifold side > and if folks don't know this, the plate can be in wrong. Could this 'base plate' be a one inch aluminum spacer with a single manifold vacuum port? Or are you referring to the actual throttle portion of the carb? That would be kind of hard to put in upside down. In any case, as in my reply to MasterBlaster, I suspect a leak in the canister purge line, which enters the carb just above the closed throttle plates, same as the EGR port. > I would figure the port you are using was blocked or it would have one > or the other types of vacuum. It's brand new, straight from the Holley factory, after sitting on some shelf for about 20 years or more. > Mike > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 > 'New' frame in the works for '08. Some Canadian Bush Trip and Build > Photos: http://mikeromainjeeptrips.shutterfly.com >>> Does anyone have any idea how much vacuum should develop at an EGR >>> port on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 27 lines] > Could this 'base plate' be a one inch aluminum spacer with a single > manifold vacuum port? Yes it could. Sometimes the kits come with multiple types of base gaskets with different holes or slots. Or are you referring to the actual throttle > portion of the carb? That would be kind of hard to put in upside down. > In any case, as in my reply to MasterBlaster, I suspect a leak in the > canister purge line, which enters the carb just above the closed > throttle plates, same as the EGR port. There is an easy test for that though I don't think it can be the trouble unless you were measuring the vacuum downstream vs at the carb nipple, just pinch the line closed. >> I would figure the port you are using was blocked or it would have one >> or the other types of vacuum. [quoted text clipped - 6 lines] >> 'New' frame in the works for '08. Some Canadian Bush Trip and Build >> Photos: http://mikeromainjeeptrips.shutterfly.com >>>> Does anyone have any idea how much vacuum should develop at an EGR >>>> port on a carburetor with the engine revved to about 2000rpm? [quoted text clipped - 49 lines] >>> 'New' frame in the works for '08. Some Canadian Bush Trip and Build >>> Photos: http://mikeromainjeeptrips.shutterfly.com Mike, I solved the problem. See my detailed reply to BigIronRam in this thread. Thanks, for the help. You were on the right track as far as the port probably being blocked goes. Whatever the reason, it just wasn't developing EGR vacuum characteristics and would not even make it to 2 pounds at 2,000rpm. > Mike, I solved the problem. See my detailed reply to BigIronRam in this > thread. Your response was to ignore the advice given. The suggestion was made that the EGR was designed to run off the very low vacuum port. From there it goes to a vacuum amplifier which uses the low vacuum signal to control the EGR using vacuum coming from intake manifold. If I understood your response - you ignored that advice and hooked it up in a different way. The low vacuum plus amplifier may or may not be how your engine vacuum lines are supposed to be configured. But it does sound like the carb was designed to work with that configuration. Is there an under-the-hood vacuum line diagram? -jim > Thanks, for the help. You were on the right track as far as the port > probably being blocked goes. Whatever the reason, it just wasn't > developing EGR vacuum characteristics and would not even make it to 2 > pounds at 2,000rpm. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> Mike, I solved the problem. See my detailed reply to BigIronRam in this >> thread. > > Your response was to ignore the advice given. My response was to investigate what a vacuum amplifier was and then to determine that the EGR system on the 87 Dakota V6 did not incorporate one. > The suggestion was made And that is *all* that it was... a suggestion. that > the EGR was designed to run off the very low vacuum port. From there it > goes to a vacuum amplifier which uses the low vacuum signal to control the > EGR using vacuum coming from intake manifold. But not in this case. I hooked up the EGR valve the way it was hooked up stock. There is no vacuum amplifier. The vacuum hose from the EGR port on the carb goes directly to the CVSCC (coolant vacuum switch cold closed) which prevents the EGR system from kicking in when the engine is closed. The vacuum line then goes directly to the EGR valve. > If I understood your > response - you ignored that advice You're starting to repeat yourself. > and hooked it up in a different way. I hooked it up in such a way that passed the smog inspection. > The low vacuum plus amplifier may or may not be how your engine vacuum > lines are supposed to be configured. Now you're getting it. > But it does sound like the carb was > designed to work with that configuration. It may be that the *carb* was designed to work that way, but the EGR system on my truck was designed to to work without a vacuum amplifier. I made it clear in the thread that the mixture control solenoid for the original, stock carb can longer be purchased and that the carb I am working with is the non-feedback version of that carb. I also made it clear in my last post to Mike Romain that I modified the carb to work like the original as far as the EGR function goes and that the mod was successful. > Is there an under-the-hood > vacuum line diagram? Of course there is. There is also one in the shop service manual. > -jim Are you the hall monitor for this group? Do you go around busting people for not following the advice of others to the letter? If so, you have too much time on your hands. >> Thanks, for the help. You were on the right track as far as the port >> probably being blocked goes. Whatever the reason, it just wasn't [quoted text clipped - 4 lines] > http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups > ---= - Total Privacy via Encryption =--- SignatureChuck Norris can fool all of the people all of the time and Chuck Norris supports McCain. McCain -- it rhymes with Hussein, Bahrain, cocaine, insane, wolfbane, chest pain and chow mein. > >> Mike, I solved the problem. See my detailed reply to BigIronRam in this > >> thread. [quoted text clipped - 3 lines] > My response was to investigate what a vacuum amplifier was and then to > determine that the EGR system on the 87 Dakota V6 did not incorporate one. Your reply made no mention of that. That is you completely ignored the advice and didn't explain why you ignored it until now. You didn't even give a hint that you comprehended what was said. > > The suggestion was made > [quoted text clipped - 6 lines] > > But not in this case. Maybe - Maybe not. How the hell would I know. > I hooked up the EGR valve the way it was hooked up stock. There is no > vacuum amplifier. The vacuum hose from the EGR port on the carb goes [quoted text clipped - 6 lines] > > You're starting to repeat yourself. When people fail to indicate they understand the advice the tendency is to repeat it. No?? > > and hooked it up in a different way. > > I hooked it up in such a way that passed the smog inspection. Then why are you trying to do additional modification? You've made a half dozen posting since you passed the test asking for help with modifications. What's that all about? > > The low vacuum plus amplifier may or may not be how your engine vacuum > > lines are supposed to be configured. > > Now you're getting it. You still don't "get" that when you fail to provide adequate information the reader has no choice but to guess what the actual facts are. > > But it does sound like the carb was > > designed to work with that configuration. > > It may be that the *carb* was designed to work that way, but the EGR > system on my truck was designed to to work without a vacuum amplifier. But given that you now have a different carburetor the range of vacuum coming from the EGR port will not be exactly the same as the original and it is possible that the way it was hooked up in connection with a vacuum amplifier might give you better performance. The EGR affects the mixture that the carb delivers. If the flow thru the EGR is not in synch with the carb mixture controls you may not be getting optimum mixture at all the different possible engine loads and RPMs. So the original advice to hook the EGR thru a vacuum amplifier still may have produced better results than you got. |
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