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Car Forum / Nissan / Nissan Cars / May 200699 Altima hesitation: I think I'm onto something!
I've posted ad nauseum about my hesitation problems off idle with my 99 Altima. Today I pulled the main ECU connector and decided to test the TPS sensor right at the ECU. I'd tested it at the sensor itself before, and it checked out, but someone on one of the Nissan web forums I posted to online mentioned he had a similar problem with a Stanza that finally turned out to be a bad TPS. Anyway, measuring the resistance of the TPS between the terminals on the ECU connector gave me the expected .5 Kohms at closed throttle, but only 1.5 Kohms at WOT. It's supposed to be 4 Kohms at WOT, and I do get this reading at the TPS itself. A bit more investigation has revealed that I seem to have a short between the power and ground lines to the TPS; I can measure about 1.2 Kohms between the two lines with the ECU terminal disconnected and the TPS connector undone. Neither wires seem to be shorted to the actual chassis ground. So, I'm trying to locate the short, but so far no luck. No change in the resistance no matter what where I try to flex the wires. I don't really want to get into pulling the whole harness apart today. What I'd like to do is pull both ends of one of the two wires, and run a jumper wire around through the window from the ECU to the TPS and see if that clears up the problem. However I'm not having any luck getting either end out of its connector. Can anyone tell me how to unlock the wire from the TPS connector, which is a waterproof 3-wire type, and from the ECU connector? Thanks in advance! >I've posted ad nauseum about my hesitation problems off idle with my 99 >Altima. Today I pulled the main ECU connector and decided to test the TPS [quoted text clipped - 17 lines] >resistance no matter what where I try to flex the wires. I don't really >want to get into pulling the whole harness apart today. In my *limited* experience, the semi-short is probably AT THE CONNECTOR ITSELF, where the wires join up with the connector pins. You will notice that unless the connector is potted, and I bet $2 of your money that it isn't, some adjacent wires are shorting via the connector itself. TAKE APART THE PLUG, and inspect it with a magnifying glass, especially the wires/solder-terminals around the wires you're concerned with. The solution is to pot the wire/solder connections, or just bend them out of eachother's way. Lg >What I'd like to do is pull both ends of one of the two wires, and run a >jumper wire around through the window from the ECU to the TPS and see if [quoted text clipped - 4 lines] > >Thanks in advance! > In my *limited* experience, the semi-short is probably AT THE > CONNECTOR ITSELF, where the wires join up with the connector pins. > You will notice that unless the connector is potted, and I bet $2 of > your money that it isn't, some adjacent wires are shorting via the > connector itself. By "potted" do you mean that each wire enters the connector in its own channel and doesn't share a common space with the other wires? If so then that's actually how the connector at the TPS is made. Also, the two wires are not adjacent at the TPS connector, they have a third wire between them, and there is no conductivity between the middle wire and the outer two. The two wires ARE adjacent at the ECU connection however, but no amount of prodding or jiggling seems to produce any variation in the resistance... I would expect at least some change if they were making partial contact there. Then again, I would also expect some variation at some point as I've been wiggling the whole harness from the TPS to the ECU, but I haven't had anything definite. > TAKE APART THE PLUG, and inspect it with a magnifying glass, > especially the wires/solder-terminals around the wires you're > concerned with. I haven't been able to get either wire out of the ECU connector yet, it looks like I have to insert something in the terminal side (not the harness side) of the connector in the hole above where the pin from the ECU goes, and pry the locking tab down, but that hasn't worked, yet. At this point, I'm seriously considering cutting one of the two wires at both ends, and jumping it with a new piece from the TPS to the ECU... the only issue there being that that becomes a weak spot in the connection and I would have to find a way to run a wire permanently. Thanks for the reply, I'll keep at it... >> In my *limited* experience, the semi-short is probably AT THE >> CONNECTOR ITSELF, where the wires join up with the connector pins. [quoted text clipped - 30 lines] > >Thanks for the reply, I'll keep at it... It doesn't have to become a weak spot, it can become the strongest part of the harness. When I do such things myself, I take a piece of air hose of the right length, slit it on one side for the length, and *tuck* the new wires into the rubber hose, then tape the hose closed along the incision that I made. A utility knife with a razor blade works best for this. Just make sure the hose/wire assy doesn't come into physical contact with hot parts, like parts of the exhaust system, and route -away- from electrically noisy things, like plug wires and coil packs. Silicone rubber in a tube can seal up the plug itself and make it waterproof. Lg > I've posted ad nauseum about my hesitation problems off idle with my 99 > Altima. Today I pulled the main ECU connector and decided to test the TPS [quoted text clipped - 26 lines] > > Thanks in advance! If I might jump in with a suggestion here. Measuring resistance can be a bit tricky due to the ability of moisture, oil, and even dust to carry a reading across your high impedance volt meter test points. These ghost shorts may be able to carry the low current from your DVOM, but would not be able to carry enough current to affect you TPS signal adversely. It would be better to measure the actual voltage signal at the PCM harness. If you back probe Pin 23 (TPS signal) at the PCM harness connector with the connector plugged into the PCM and the ignition switch on, engine off, you should read 150 mv to 850 mv at closed throttle. As you depress the accelerator, the voltage should climb steadily to a wide open throttle reading of 3.5 v to 4.7 v. Having an oscilloscope would be nice because you could watch the voltage trace for any glitches, but if you are very observant and steady you may be able to catch any glitch by seeing the voltage fail to climb steadily on your DVOM. If your meter has selectable voltage ranges, use the lowest ranger possible to view 5 volts. If it has an analog display be sure to watch it carefully. If you do not get the expected voltage ranges then be sure to verify that you have a good 5 volt reference voltage at the TPS and then perform a voltage drop test on the TPS negative wire to ground. Any voltage reading across the ground return indicates unwanted resistance that needs to be corrected. Just testing resistance readings is not always a very conclusive diagnosis for TPS circutry.  SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green > If I might jump in with a suggestion here. Measuring resistance can be a > bit tricky due to the ability of moisture, oil, and even dust to carry a > reading across your high impedance volt meter test points. These ghost > shorts may be able to carry the low current from your DVOM, but would not > be > able to carry enough current to affect you TPS signal adversely. It would Good point. It's not a very high resistance short in relation to the resistance expected at WOT though... 1.2 Kohms vs 4, so it seems like a short of that level would have an effect. > be better to measure the actual voltage signal at the PCM harness. If you > back probe Pin 23 (TPS signal) at the PCM harness connector with the [quoted text clipped - 9 lines] > an > analog display be sure to watch it carefully. I'll give that a try and see what I get. > If you do not get the expected voltage ranges then be sure to verify that > you have a good 5 volt reference voltage at the TPS and then perform a [quoted text clipped - 3 lines] > Just testing resistance readings is not always a very conclusive diagnosis > for TPS circutry. Thanks for those suggestions, I will test all of those things and post back. Hi Kevin, > Just testing resistance readings is not always a very conclusive diagnosis > for TPS circutry. I just read your other post RE: Testing automotive electronics, and realized you may have thought I was testing the TPS directly and seeing the short between two pins on the TPS itself. What I'm actually seeing is a short between two separate wires in the harness between the ECU and the TPS, with BOTH ENDS of said harness unplugged. So in a normal situation, there should be NO conductivity between the two wires. I also measured the TPS resistance at the ECU with the TPS end of the harness connected, and the ECU connector disconnected, and this was where I was seeing about 1/3 of the expected resistance at WOT. > Hi Kevin, > [quoted text clipped - 7 lines] > BOTH ENDS of said harness unplugged. So in a normal situation, there should > be NO conductivity between the two wires. Lets see if I am getting this right.. With both the ECM and the TPS disconnected from the harness. You are getting a reading of 1200 ohms between the TPS signal wire and the Referance voltage wire? You should get an infinite reading during that test, unless (and I would have to check a wiring schematic) there is some other circuit in parrallel with the TPS on your vehicle. Keep in mind that the Reference voltage wire is connected parrell to many other sensors. Only the Signal wire (to pin 23) is a direct wire from the TPS center pin back to the ECM. Do you have a good wiring diagram? Look it over carefully and be sure you are testing the correct wires. > I also measured the TPS resistance at the ECU with the TPS end of the > harness connected, and the ECU connector disconnected, and this was where I > was seeing about 1/3 of the expected resistance at WOT. Well, I can see where that might be a problem, but don't be fooled by some continuity across the circuit due to possible contamination. That sort of short will not usually carry enough current to skew the TPS signal measurably, but it will show up on an ohm meter. If there is indeed a hard short across the two wires the reading would usually be closer to 0 Ohms. There again, be sure you are testing the correct wires. Double check. Still, checking the signal voltage is a much more reliable test with less chance of error. My post on testing wasn't aimed at you, I just thought it might be some helpful information to other readers. I hope you didn't take it as a slight on you capabilities. The truth is, you seem to have a pretty go grasp on the situation. Anything I can do to help is offered gacefully. SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green > Lets see if I am getting this right.. With both the ECM and the TPS > disconnected from the harness. You are getting a reading of 1200 ohms > between the TPS signal wire and the Referance voltage wire? You should get Well, actually it is between the signal ground wire and the reference voltage, but yes. In my original post I was thinking it was between the TPS signal & the signal ground, but that's not the case. > an infinite reading during that test, unless (and I would have to check a > wiring schematic) there is some other circuit in parrallel with the TPS on [quoted text clipped - 4 lines] > diagram? Look it over carefully and be sure you are testing the correct > wires. I've got the factory service manual and it doesn't show any other devices connected in parallel, at least not in the TPS section of the book. Maybe one of the overall schematics would tell a different story. If there are multiple devices sharing the same reference voltage signal I would expect they are tied together inside the ECU and not all joined somewhere inside the harness? >> I also measured the TPS resistance at the ECU with the TPS end of the >> harness connected, and the ECU connector disconnected, and this was [quoted text clipped - 7 lines] > There again, be sure you are testing the correct wires. Double check. > Still, I'm 99% sure I have the right wires; I can test either at the TPS end or the ECU end and I get the exact same resistance between the supposedly unattached wires, and if I test from one end of either wire to the other end of the same wire, I get a hard short, so that would seem to indicate I have the right wires. I did think it was strange that it's not a hard short between the two wires though, and also strange that it does not vary at all, even with all the moving I did of the wiring harness. The most change I saw was maybe .03 Kohm and I couldn't ever be sure that was due to my fiddling with the wires or just random changes in connection strength. > checking the signal voltage is a much more reliable test with less chance > of > error. I'm anxious to give that a try in the morning and hopefully learn for sure if there is a problem here or not. > My post on testing wasn't aimed at you, I just thought it might be some > helpful information to other readers. I hope you didn't take it as a > slight > on you capabilities. Not at all, it just sounded as if you had misunderstood my original post so I wanted to clear that up. > The truth is, you seem to have a pretty go grasp on the > situation. Anything I can do to help is offered gacefully. And I appreciate that. As does the rest of the group I'm sure. Anyway, I'll do some testing of the voltages in the morning and report back; thanks again for the input. >> Lets see if I am getting this right.. With both the ECM and the TPS >> disconnected from the harness. You are getting a reading of 1200 ohms [quoted text clipped - 4 lines] > voltage, but yes. In my original post I was thinking it was between the > TPS signal & the signal ground, but that's not the case. Now that I think about this, something's not adding up. Maybe I've got it backwards in my head after going over it so many times. But if the semi-short is between reference and ground, then theoretically the current should pass through to the TPS rather than cross the 1.2Kohm bridge, unless the resistance between the ref. voltage and signal ground is greater than 1.2K. Obviously a test of voltages will show the truth... I fault find electronics for a living so here's my thoughts......... You really need to find out if that cable has a straight run between ECU and TPS with no branches off to other sensors etc. There wouldn't normally be any such branch but who knows, all I know is that my Nissan Primera hasn't got any. If it's a straight run of cable then the technique for finding where this 1K2 resistance is is to measure it while heating up the plugs and cable with a hot air gun. The reading will 99% of the time change when you've found the right spot. There's a possibility the reading could be a protection diode inside a plug and may not appear on the circuit diagram, if that's the case you'll get a different reading with the meter leads reversed. Some meters have a diode range and you'll get a reading of about 0.6v one way and no reading the other. > > Lets see if I am getting this right.. With both the ECM and the TPS > > disconnected from the harness. You are getting a reading of 1200 ohms [quoted text clipped - 3 lines] > voltage, but yes. In my original post I was thinking it was between the TPS > signal & the signal ground, but that's not the case. There in lies the problem. The reference voltage (sensor power supply 5 Volts) wire leaves the ECM and branches out to all the sensors that need reference voltage. The signal ground also leaves the ECM and branches out to all the sensors that have a signal ground. You are reading the parrellel resistance of all the other sensors in the system if you check from reference to signal ground. You would have to disconnect every sensor to show an open circuit between those two wires. You need to be checking from reference (ECM pin 49, Red wire) to TPS signal (ECM pin 23 , Yellow wire) to find the specified 4,000 ohms at WOT. It will all make sense to you if you could look at the whole wiring diagram and get an understanding of the circuitry. Kevin BTW, Engine performance electronics is my favorite type of work. <grin> > > an infinite reading during that test, unless (and I would have to check a > > wiring schematic) there is some other circuit in parrallel with the TPS on [quoted text clipped - 56 lines] > Anyway, I'll do some testing of the voltages in the morning and report back; > thanks again for the input. Maybe this will help. Here is a link to a good explaination of a TPS It is Generic in nature but does apply to your type of TPS. http://www.autoshop101.com/forms/h33.pdf Kevin > > > Lets see if I am getting this right.. With both the ECM and the TPS > > > disconnected from the harness. You are getting a reading of 1200 ohms [quoted text clipped - 96 lines] > back; > > thanks again for the input. > There in lies the problem. The reference voltage (sensor power supply 5 > Volts) wire leaves the ECM and branches out to all the sensors that need [quoted text clipped - 8 lines] > you could look at the whole wiring diagram and get an understanding of the > circuitry. Well, you were right! I tested the voltage on pin 23 and it seems to be fine, it's within spec and free of any dropouts or spikes from closed to WOT. I think what I was seeing in the resistance checks was something in the branch of the TPS wiring that goes to the transmission controller in the automatic models. The service manual has it in the schematic with a broken-line box around it for automatics, so I just discounted it right away, but I guess there is probably still something attached there maybe with a resistor installed to close the circuit. So thanks for your guidance Kevin, if you hadn't made me second guess myself, I probably would have cut the wires by now and tried to run new ones... and would have been pretty damn depressed when it made no difference. Luckily all I have to deal with instead is a little dose of humility, heheh. Regards, > > There in lies the problem. The reference voltage (sensor power supply 5 > > Volts) wire leaves the ECM and branches out to all the sensors that need [quoted text clipped - 24 lines] > > Regards, Now that you have resolved that issue.......................... What was the original problem you were trying to diagnose. Maybe we can figure that out. SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green > Now that you have resolved that issue.......................... What was > the > original problem you were trying to diagnose. Maybe we can figure that > out. Well, since you asked... :) what I'm dealing with are 3 or 4 different symptoms that I think (and hope) are related to the same underlying issue. They are: 1. The car wants to rev fast when starting, warm or cold. This morning it was about 10 deg. C and when I started it revved up to 2k which I think is a bit high. That's not so bad on its own, but until it warms up, the car wants to rev to 2k or so every time I come to a stop and put in the clutch. Also, when I start it warm it still wants to rev to 2k, and usually revs that high, comes down to 1500, and then often revs back up once or twice, or just hangs, before coming down to idle. As an aside to the above, this car has a fast idle cam that opens the throttle as the coolant temp decreases. I had that disabled for a few weeks and the over-revving when cold was gone. It still ran a little fast until it warmed up, but the highest I ever saw was about 1500 rpm. I'm sure this would not be a good solution in the winter though. Maybe I could adjust the FIC to open the throttle less, but as far as I can tell, it and the throttle plate are both adjusted properly. 2. Warm or cold, the ECU seems to want to rev the engine (open the IAC valve) whenever I touch the gas pedal. If I'm stopped and in neutral, I can ease into the pedal until the revs reach about 1000 RPM, but at some point slightly above those revs, the engine will speed up to 2000 RPM without my opening the throttle any further. It won't return to idle until I release the throttle. 3. More noticeable when cold, but also occuring when warm, is an abrupt jolt when I ease into or out of the throttle at crusing speed. This is obviously more noticeable in lower gears, but it seems to be most apparent around 2,000 RPM. I suspect the same behavior I see in the above point is what's causing this. 4. Last, the car has a slight hesitation off idle, when I step into the gas quickly. The tach will visibly dip for a split second before anything happens. This is most apparent when fully warmed up, and, even more so when having just started the car after it's been sitting for a few minutes and is still warm, eg, stopping to get gas and then restarting. Here's what I've done to try and diagnose: Tested TPS, OK Tested coolant temp sensor, OK Tested intake air temp sensor, OK Tested O2 sensor via onboard test in ECU (blinked LED about 10 times in 10 seconds at 2000 rpm) Tested MAF sensor output, seems OK. Tested fuel pressure, OK Tested absolute pressure (vacuum) sensor, OK. Cleaned EGR valve and passageways, also disconnected vacuum line to EGR valve, no change. Cleaned throttle body and plate. I've put in new plugs, wires, dist. cap & rotor, and air filter recently. I've had the dealer do their "regular" injector cleaning. I've run 1/2 bottle of Lucas upper cylinder lubricant. Smoothed out acceleration quite a bit, but no change in the above symptoms. I think that's about it. I think I'm to the point now where it's going to take a tech with a CONSULT scanner to get a look at what the ECU is doing when all this is happening to get to the bottom of it.. but as always I'm willing to try anything anyone can suggest. >> Now that you have resolved that issue.......................... What was >> the [quoted text clipped - 65 lines] >get to the bottom of it.. but as always I'm willing to try anything anyone >can suggest. Vacuum leak. Check all Vac hoses but especially intake manifold. Do propane test. Lg > Vacuum leak. > Check all Vac hoses but especially intake manifold. > Do propane test. I've done what I could in this respect. Taped off the intake tube and blew into the idle bypass pipe, everything held pressure. All the vac lines I can find are fine, and I tried shooting TB cleaner around the intake manifold runners where they bolt to the head, with no change in idle. I guess it's not uncommon to have a leaking manifold gasket in this car, but it doesn't *seem* like I have one. >> Vacuum leak. >> Check all Vac hoses but especially intake manifold. [quoted text clipped - 6 lines] >guess it's not uncommon to have a leaking manifold gasket in this car, but >it doesn't *seem* like I have one. Restricted air filter fuel pump or pressure regulator defective pull the PVC valve to be sure it is working correctly >>> Vacuum leak. >>> Check all Vac hoses but especially intake manifold. [quoted text clipped - 9 lines] >Restricted air filter >fuel pump or pressure regulator defective X>pull the PVC valve to be sure it is working correctly PCV valve ( positive crankase ventilation valve ) > Restricted air filter > fuel pump or pressure regulator defective > pull the PVC valve to be sure it is working correctly PCV is the only thing I haven't checked, because apparently the valve is buried up underneath the intake manifold, and I've heard from a few different people that they've never seen one go bad in a Nissan. Not that that's any reason not to check mine, but that combined with its location has made it a lower priority. I'll keep it in mind though as more things are elminated. >> Restricted air filter >> fuel pump or pressure regulator defective [quoted text clipped - 6 lines] >made it a lower priority. I'll keep it in mind though as more things are >elminated. location location location. I know exactly what you mean. OTOH, it is a $3 US part, and it is probably a good idea to _replace_ it if you're going to the trouble of digging the old one out. You want a *nice vacuum* there when the engine is running, sucking fumes out of the crank case. Just put your hand over the end of it when you pull it out of the engine port, and you should feel a nice vacuum. Then *jiggle it* to see if the weight is free to move back and forth, and doesn't *stick.* Or like I said, just replace it. If it has never been replaced before, for the price, this should be done anyhow. Lg >>Now that you have resolved that issue.......................... What was >>the [quoted text clipped - 65 lines] > get to the bottom of it.. but as always I'm willing to try anything anyone > can suggest. Like others suggested, look into replacing the PCV. Also, is the idle screw missing? On the throttle body, there should be a screw in place to stop the cable actuated butterfly valve from resting at the dead stop position, so to speak. When I bought my Sentra from a used dealer, that screw was missing, and acceleration off of idle was always always abrupt. Replacing that fixed it. Always do the simple things before you go Einstein on the electronics, I always say:) CD > Like others suggested, look into replacing the PCV. Also, is the idle Yeah. If I can get under it this weekend I"ll see how accessible it is. In all honesty though, and not to knock anyone's suggestions, the problems seem so consistent and ever-present that it seems like more of an adjustment or calibration problem than a stuck PCV. Not that I really have any experience to base that on... > screw missing? On the throttle body, there should be a screw in place to > stop the cable actuated butterfly valve from resting at the dead stop > position, so to speak. When I bought my Sentra from a used dealer, that > screw was missing, and acceleration off of idle was always always abrupt. > Replacing that fixed it. Nope, my screw is there. I have adjusted it in the past to lower my idle, because my idle screw was seized, but I've fixed that problem and returned the stop screw to its original position. The abruptness on and off idle has always been there though. Also, this car has a fast idle cam that keeps the throttle open well clear of that screw when cold, and the problem is worst when cold, so the problem is *probably* elsewhere... > Always do the simple things before you go Einstein on the electronics, I > always say:) Hey, I'm all for that! Just running out of simple things to do :) >> Like others suggested, look into replacing the PCV. Also, is the idle > [quoted text clipped - 21 lines] > > Hey, I'm all for that! Just running out of simple things to do :) OK, I found your older thread and was wondering, did you replace the coolant temp sesnor? It's worth a shot. Cheap part, easy replacement. Usually a bad temp sensor has the symptom of bad gas mileage and it may cause a not so stable low rpm operation as well, as you're experiencing. Also, if it's not that, then perhaps you have a bad fuel injector. Just a mildly educated guess. CD > OK, I found your older thread and was wondering, did you replace the > coolant temp sesnor? It's worth a shot. Cheap part, easy replacement. > Usually a bad temp sensor has the symptom of bad gas mileage and it may > cause a not so stable low rpm operation as well, as you're experiencing. Yeah, I have wondered about that sensor for a long time, but haven't replaced it yet. I priced it at $30 one weekend and they would have had to order it in, so I decided against it for the time being. I have tested mine though with my meter and it seems accurate warm and cold, so... ? > Also, if it's not that, then perhaps you have a bad fuel injector. Just > a mildly educated guess. Could be I suppose. The idle seems slightly rough but it's not like it's running on 3 cyls. I'm not sure testing injectors is still at the level I want to get into in my driveway with an hour to spare on any given day :) > > Now that you have resolved that issue.......................... What was > > the [quoted text clipped - 65 lines] > get to the bottom of it.. but as always I'm willing to try anything anyone > can suggest. I would have to do some digging through the manual, but I think your car is also equipped with a throttle or idle tracking switch. That is another switch besides the TPS. It has contacts that tell the ECM when the throttle is all the way closed and all the way open. If you have a repair manual, try looking up the test procedures for that switch. I think it may even be adjustable. I do know that your symptoms are similar to other vehicles I have worked on that did have problems with the idle tracking switch. I have also seen similar symptoms from faulty gear selector and clutch switches. These are the ones that tell the ECM you are about to load or unload the engine. I'm not sure if your car is equipped with those switches, but if it is, then they need to be checked. BTW. All those switches will not normally set a DTC when they malfunction because the computer just accepts whatever position they indicate as fact. As other have replied, vacuum or air induction leaks will also cause similar symptoms. Check brake booster, PCV, air duct to filter, etc Don't guess you have a smoke machine? <grin> I'll be in training all this coming week so I may not get to post until late evenings. Hope this will give you some more stuff to consider though. SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green > I would have to do some digging through the manual, but I think your car > is [quoted text clipped - 4 lines] > try looking up the test procedures for that switch. I think it may even be > adjustable. I do know that your symptoms are similar to other vehicles I It does have such a switch, but, it's part of the same unit as the TPS, and according to the service manual, it's not used for engine control. It may be only used for the transmission in automatic models (mine is manual). FWIW I did adjust it according to the manual, but had no effect on the problem. Also, when the car is cold, the throttle is kept open by that fast idle cam, beyond the point where the closed throttle switch is closed anyway -- and this is when the abruptness is at its worst. The procedure for adjusting the switch requires the engine to be fully warmed up first, which I'm sure is so that the fast idle cam won't be holding the throttle open when you're trying to adjust it properly. > have worked on that did have problems with the idle tracking switch. I > have [quoted text clipped - 3 lines] > it > is, then they need to be checked. I've wondered about both of those things, but the throttle closed switch seems to be a non-issue.. and I did a quick test of the clutch switch by pressing it with the cruise control on, and it did cancel the cruise, so as long as there is only the one switch on the clutch, that would seem to be fine. > BTW. All those switches will not normally set a DTC when they malfunction > because the computer just accepts whatever position they indicate as fact. I kind of figured as much, which is why I got into testing the TPS in depth. It seems like that kind of a problem to me. > As other have replied, vacuum or air induction leaks will also cause > similar > symptoms. > Check brake booster, PCV, air duct to filter, etc Save for the PCV, all done. > Don't guess you have a smoke machine? <grin> Sadly no, I just read about that technique yesterday. But, I did try pressurizing the intake manifold manually and there was no leakage of any serious amount... a very slow one around the EGR valve I think, but that may have been due to the wrong "polarity" of pressure in the system. > I'll be in training all this coming week so I may not get to post until > late > evenings. Hope this will give you some more stuff to consider though. Absolutely, I certainly appreciate any and all ideas you or anyone else has. Thanks again, Another thing I've noticed lately is the engine doesn't seem to speed up when I turn the wheel left or right at idle, and it will often rev way down to 500 rpm or below when I have eg the blower on full with the headlights and rear defrost on. I don't know if this is possibly related in any way to the hesitation / overrevving, but I have been meaning to mention it. It's almost as if the ECU in general isn't getting the proper indication of engine speed, or, the fact that it's at idle... > Another thing I've noticed lately is the engine doesn't seem to speed up > when I turn the wheel left or right at idle, and it will often rev way down [quoted text clipped - 3 lines] > almost as if the ECU in general isn't getting the proper indication of > engine speed, or, the fact that it's at idle... That sounds like bad electrical connections. When you turn the wheel, the power steering puts more of a load on the motor, the rpms drop. Because the rpms dropped, and they are so low to begin with being just above idle, the ALT output then drops, dangerously low, so low that bad grounds and other electrical gremlins make themsleves more obvious. Because the ALT's output is so low, all the readings to the ECU get off base, the O2 sensor is slightly off, the temp sensor etc, you get the idea. So your car runs funny. In the other scenario, when you maximize the load on the ALT by putting th fan on full, defroster, headlights, etc, you are working your ALT to the max. Any corroded connections will have a great effect on its ability to do its job delivering ampage to the electrical system. Solution? Thoroughly check and clean all major electrical connections such as the battery, all the alternator connections, the ground connections to the engine block etc. And I mean dis-connect the connections, clean them, then put them back. If after cleaning them you still experience these problems, then maybe your ALT needs a rebuild, replace brushes etc. Hope this helps CD or perhaps the power steering pressure switch is bad and not telling the computer to speed up the engine when the power steering is being applied??? > > Another thing I've noticed lately is the engine doesn't seem to speed up > > when I turn the wheel left or right at idle, and it will often rev way down [quoted text clipped - 6 lines] > That sounds like bad electrical connections. When you turn the wheel, > the power steering puts more of a load on the motor, the rpms drop. The computer should pick the idle back up when it gets a signal from the power steering pressure switch telling it that the engine is being loaded. Could be a bad switch or an idle controller problem. > Because the rpms dropped, and they are so low to begin with being just > above idle, the ALT output then drops, dangerously low, so low that bad > grounds and other electrical gremlins make themsleves more obvious. > Because the ALT's output is so low, all the readings to the ECU get off > base, the O2 sensor is slightly off, the temp sensor etc, you get the > idea. So your car runs funny. I can agree that the engine performance problems may be due to some electrical problems, but your reasoning is way off. The computer system operates all it's sensors at 5volts reference, so the battery would have to be too discharged to even fire the injectors before the sensor voltages would be affected. I do see what you are getting at though. When voltage is low resistance has a greater affect, and the problems may well be related to bad connections or grounds. > In the other scenario, when you maximize the load on the ALT by putting > th fan on full, defroster, headlights, etc, you are working your ALT to [quoted text clipped - 5 lines] > connections to the engine block etc. And I mean dis-connect the > connections, clean them, then put them back. It would be a lot easier to just check the voltage drop across the ground circuits rather than try to find and clean them all. > If after cleaning them you still experience these problems, then maybe > your ALT needs a rebuild, replace brushes etc. > > Hope this helps > > CD I think the alternator output is not suspect in the hesitation and erratic idle complaint originally posted. When all the obvious and simple things check out ok, then it is time for the big guns. JM probably needs to have a shop with all the necessary equipment trouble shoot this one. All the obvious stuff hasn't turned up any problems. Of course, if he has the time and patience then he can keep pecking at it until he might stumble across the culprit. Good luck JM. >>>Another thing I've noticed lately is the engine doesn't seem to speed up >>>when I turn the wheel left or right at idle, and it will often rev way [quoted text clipped - 37 lines] > low resistance has a greater affect, and the problems may well be related to > bad connections or grounds. How is it way off? The sensors expect 5 volts, so somewhere in the system the 12 volts from the battery is being reduced to 5 volts. But if the battery is not pushing out 12 volts, like say 11 or 10, then the other end of the voltage divider is not pushing out 5 volts but instead 4 or 3 volts. Voltage dividers tend to not have the ability to compensate greatly for fluctuations, so less than 12 volts on one end would mean less than 5 volts on the other. >>In the other scenario, when you maximize the load on the ALT by putting >>th fan on full, defroster, headlights, etc, you are working your ALT to [quoted text clipped - 8 lines] > It would be a lot easier to just check the voltage drop across the ground > circuits rather than try to find and clean them all. OK, check and clean all ground connections. That's simpler. >>If after cleaning them you still experience these problems, then maybe >>your ALT needs a rebuild, replace brushes etc. [quoted text clipped - 5 lines] > I think the alternator output is not suspect in the hesitation and erratic > idle complaint originally posted. Think about it The ALT's output rating, say like 80 amps, is usually determined when the car's rpm is at something like 3000 rpms. When the engine's rpms go low, the alternator still must produce a minumam amperage, say 15 amps at 1000 rpms. But a sick alternator will go below that and may contribute to a cars erratic behaviour. I'm not sayin that the problem is the alternator, just a possibility. > When all the obvious and simple things check out ok, then it is time for the > big guns. JM probably needs to have a shop with all the necessary equipment > trouble shoot this one. All the obvious stuff hasn't turned up any problems. > Of course, if he has the time and patience then he can keep pecking at it > until he might stumble across the culprit. Good luck JM. > How is it way off? It's way off because you assume the power supply for the 5 volts is unregulated. You look at it as if you were the first person to think of the negative consequences of not having a stable reference voltage. The fact is, if your alternator dies the car will continue to run normally off the battery until the battery is almost completely dead. And when the battery does get really low its the high voltage ignition system that is the first to fail. -jim >The sensors expect 5 volts, so somewhere in the > system the 12 volts from the battery is being reduced to 5 volts. But if [quoted text clipped - 41 lines] > > Of course, if he has the time and patience then he can keep pecking at it > > until he might stumble across the culprit. Good luck JM. A 5v regulator costs next to nothing so there's no doubt one would be used. Any voltage between about 7v and 16v from the alternator/battery would give out the same 5v. > A 5v regulator costs next to nothing so there's no doubt one would be used. > Any voltage between about 7v and 16v from the alternator/battery would give > out the same 5v. Thanks, and thanks also to KM who explained it to me as well in an email. CD |
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