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Car Forum / Porsche / Porshe 944 / November 2006continuing puzzlement, 944S
ok guys, this is getting silly. Car = high mileage (225K) 87 944S. It's running rich. Fuel pressure is too high. this is because vacuum is too low. I can't find any vac leaks, all vac lines are connected correctly, etc. Compression is pretty good (between 200 and 210 on all 4 cyl), so I don't think it's blowby that's causing the problem. Plugs show raw fuel on occasion, a few days ago the car "flooded" while running. I pulled the injectors and cleaned them, put them back - car runs reasonably well, but it's still running rich. So, what to do? any hints? why would manifold vac be way too low? I've tried blocking off the main line to the brake booster, that doesn't raise vac, I've changed intake gasket, replaced air flow sensor (that helped make car run a lot better), I've tried all the usual tricks to find a leak, I've changed oil seals and replaced the o-ring on the dip stick and so on --- there has got to be some reasonable explanation here, I don't want to just shotgun this  Signaturebill to email me, to to my web page, www.wbnoble.com and find my email or unscramble the following by removing spaces and correcting the obvious spelling errors wil lia m_b_n obl e at msn daught com -- Posted via a free Usenet account from http://www.teranews.com Hi Bill, it's good that you've ruled out all of the obvious things. I assume you do your testing with a vacuum gauge connected to the manifold, to come to the conclusion that vacuum is low? This system has lots of little rubber elbows and fittings, plus a vacuum resevoir (to provide adiquate vacuum to run the climate control system, etc while you're under full throttle (when you aren't making vacuum). Most of my experience is with turbos, but on your car, vacuum is used for the fuel pressure regulator, the fuel damper, the heater valve, climate control flaps and power brakes -- perhaps more. All of these things have those rubber elbows, which, as the car reaches 20 years old, start to dry out and crack. The best way I've discovered finding a leak is by making a tester out of an old fuel filter -- cut it in half, take out the guts, and put an air compressor nipple on one half. You can now take out your mass air flow sensor and fit this into the boot. Tighten the hose clamp and you have an air tight seal. Set the air pressure on your compressor to about 15 psi, and hook it up to your new tool. You are now ready to listen for leaks. FYI, you may hear a hissing from under the valve cover if an intake valve is opened. One more thought... at what RPM does it run rich? Or can you tell? How are you measuring fuel pressure? How long have you had the car? Is it possible someone put on a higher pressure fuel regulator? is it possible that your fuel pressure regulator is bad? Have you used an exhaust gas analyser to determine if it's running rich? Perhaps an injector is worn, so it doesn't seal completely shut? You could also have a bad idle control stabilizer... that would cause poor "startability" (like flooding) and it could be an air leak around a closed throttle body, so vacuum would be poor at idle. At WOT (wide open throttle) it would run just fine, because the air, regardless if it goes through the throttle body or if it goes throught the idle control stabilizer, would be accounted for by the mass air flow sensor -- so fuel air mixture would be correct. Now that I think about it, this would be the first place I'd start looking... FYI, pressurizing the intake system would NOT find a bad idle control stabilizer... Good luck! > ok guys, this is getting silly. > Car = high mileage (225K) 87 944S. It's running rich. Fuel pressure is too [quoted text clipped - 18 lines] > > wil lia m_b_n obl e at msn daught com thanks for the responses - some answers: 1. measured vac several ways including measuring at the connection to press reg and at the venturi connection to the manifold (note that the S has a very different manifold from turbo or NA) 2. measured fuel pressure by removing the ball and nut (which on the S is on the side of the fuel rail) 3. no known vac leaks in hoses, replaced several, I don't think it's that kind of problem 4. did the test of pressurizing manifold, air leaks out the block - it's leaking past the rings, didn't find a position where all valves are closed - maybe I could try that again - put about 5 PSI into it, did't want to go much higher for fear of damaging some old rubber parts - saw no leaks at manifold or any external part even when sprayed with soap solution - this procedure is in the factory service manual, I've done all that is in that manual 5. daugher's car, have had it for a bit over a year - it's been definately worked on/over, it had obviously broken a timing belt before I got it, had recently overhauled head with new chain guide (dual cams), etc. I've replaced the balance shaft and front crank seal and the air flow meter (and other stuff not relevant to this) 7. I don't have a hydrocarbon meter, but it certainly idles rich, and under heavy accel you can see black smoke from the tail pipe. 8. have removed and cleaned the idle control valve. Manifold had a lot of oil and greasy stuff in it which we cleaned out, idle control is good, idle speed is stable and rock solid. Throttle switches work correctly (when I got the car the throttle plate was misadjusted, it's right now, per manual) 9. the measured data is in a booklet in the car, I'll see if I can get the measured vac values and fuel press values from my daughter - what I do remember is that the vac was low and pressure high based on the diagnostic chart and data in the factory manual. so??? > Hi Bill, it's good that you've ruled out all of the obvious things. I > assume you do your testing with a vacuum gauge connected to the [quoted text clipped - 73 lines] >> >> wil lia m_b_n obl e at msn daught com SignaturePosted via a free Usenet account from http://www.teranews.com Hmmm... this is a good puzzle. It may be premature to assume the rings are bad from that intake pressurization test -- I believe the intake cam duration is over 200 degrees of crank rotation. 4 (sets) of intake valves, space evenly throughout two crank revolutions, and one valve will always be a little opened. A real leakdown test is the best way to test rings, but your compression numbers sound good, so the rings are probably adiquate. I rebuilt my turbo engine after 110k miles, and found very little ring wear -- in fact, I replaced many components that were just fine. If you're seeing a puff of black smoke under acceleration and your spark plugs show signs of richness, perhaps it's more of a fuel delivery problem (injectors not metering out the right volume). It could be something like the O2 sensor, do you know anyone with the Motronic tester? Have you checked your timing belt marks? (maybe you got the cams one tooth off when you did the front seals) If the cam timing (intake specifically) isn't synched up right, you might not get a full charge of air in the cylinder. If the injectors are working properly, then you'd have a rich fuel air ratio... Is it possible that the timing chain between cams could be off a tooth? This cam timing is the theory I'm leaning towards now... Of course I was wrong last time with the idle control stabilizer. Good luck! > thanks for the responses - some answers: > 1. measured vac several ways including measuring at the connection to press [quoted text clipped - 109 lines] > >> -- > >> Posted via a free Usenet account from http://www.teranews.com thanks for all the great suggestions - let's see here: 1. I tried the WD-40 approach, and I tired it with ether also - no effect 2. puff of black smoke could very well be too rich, it's black not blue 3. it could be the O2 sensor, but I doubt it because at idle and max throttle the sensor is not part of the control circuit (at least that is my undersntanding) 4. the timing is correct - on the S, it's a real pain, you crawl under the car to see the little mark on the flywheel (there is no way to see the mark on the top) - I did have a problem with the belt, I had to take the tensioner to my mill and enlongate the adjustment slot by about 6 mm before I could get the new belt on with reasonable tension - but the car was running rich before that. 5. I pulled the plugs to look this weekend, they were all about the same (not a problem with one cyl) and were all way to rich. Now, it is POSSIBLE that the injectors are no good - I removed all of them, cleaned them with carb cleaner (I think I posted the procedure a while back) - since I got the car used, who knows if the prior owner put oversized injectors in it - but that's an expensive proposition - I'll have to check and see if the #s match up to the PET6 - the S uses different injectors than the NA. But, wrong injectors wouldn't explain the vacuum being too low, would it? > Hmmm... this is a good puzzle. It gigantic snip of all the history ----------------- SignaturePosted via a free Usenet account from http://www.teranews.com Injectors in poor condition should not effect vacuum... At least not in a way I can think of. I think the tips of your injectors might be worn -- it's essentially a needle valve that's open and shut with an electromagnetic coil. However, they can be worn so that when they are "shut" fuel still leaks out of them. This would make little puddles of fuel on the tops of the intake valves -- when the injectors open for their normal cycle, they'll add to this already deposited fuel, making for a rich mixture. It really seems quite simple -- either the car is being starved of air on the intake side, or the fuel delivery is providing too much. :) But you already knew that! There is a little mixture adjustment screw on the throttle body that I've seen people mess with to "fix" idling problems, when they should have figured out what was really causing the problem (like a misaligned TPS). I believe it says in the manual that you're only supposed to mess with that screw with a gas analyzer to make sure you're doing it right. Perhaps someone messed with it, and it's not getting the proper air flow at idle (however, this should make for more vacuum (isn't that an oxymoron? If vacuum is a state of nothingness, how can you have more of it? More nothing is really less something...)) What puzzles me is that your two symptoms are really contrary to each other. Low vacuum means more air flow into the intake manifold, which makes for a lean mixture. But also being rich, you're saying that you have both more fuel that desired and more air than desired. Perhaps the car IS making the proper amount of vacuum (does it have original cams?), and it's just less than other cars out there. The old 911 RS's with the mechanical fuel injection have mechanical fuel injection specifically for that reason. Because of the cam profiles, the intake and exhaust valve overlap is so long, the engine hardly develops vacuum. Certianly not enough vacuum to draw air through a carb and have it atomize the flood of gas required to make the desired power. So the answer was to have a mechanical injection pump that runs off of a timing belt. This way the pump can make enough pressure and can be timed to squirt the gas into the manifold at the right times. You'll need more than luck now! > thanks for all the great suggestions - let's see here: > [quoted text clipped - 23 lines] > > gigantic snip of all the history ----------------- aaah, thanks, I think. I believe the car is running rich due to high fuel pressure. I confirmed that the pressure is about 10 psi (from memory) high - my notes are in the car and the car is 110 miles away right now. The fuel pressure regulator raises and lowers pressure based on engine vacuum - I confirmed that if I put a hand vac pump on the regulator, I could lower the pressure. The vac measures low - I don't remember the number, but it was about half of what it should have been, again from memory. I have put a volt meter on the O2 sensor and seen that it changes value as I rev the engine, so it's not dead - of course that doesn't mean it 's working properly, but I really think it's something in the fuel/vacuum circuit - I just can't find it. grrrr > Injectors in poor condition should not effect vacuum... At least not > in a way I can think of. I think the tips of your injectors might be [quoted text clipped - 72 lines] >> >> gigantic snip of all the history ----------------- SignaturePosted via a free Usenet account from http://www.teranews.com Perhaps you just have the wrong fuel pressure regulator on there. I know that for the turbo cars, a performance chip set requires a pressure regulator with a higher setting. I think Lindsey Racing, or a place like that, makes an adjustable pressure regulator. Ah, I found the page: http://www.lindseyracing.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=LR&Ca tegory_Code=944FUELREGULATOR > aaah, thanks, I think. I believe the car is running rich due to high fuel > pressure. I confirmed that the pressure is about 10 psi (from memory) [quoted text clipped - 88 lines] > >> -- > >> Posted via a free Usenet account from http://www.teranews.com ok, my daughter found the fuel pressure measurement I had made about 6 months ago, at idle I had measured 52 pounds. reading some various related info from the service manual: valve timing (we mentioned that a few days back): intake opens 4deg after TDC, closes 40 deg after TDC exhaust opens 36 deg before TDC, closes 4 deg BTDC from secton 24 of the service manual, vacuum on pressure regulator at idle speed = 3.3 +- 0.2 bar since one bar = 14.5 psi, 3.3 bar = 47.8 psi without vacuum on pressure regulator, pressure should rise to 3.8 bar = 55 psi so you see that it looks like the pressure is a bit on the high side. for test point 19, "intake system leaks", it says to pressurize to 0.5 bar (about 7 psi) and find leaks, and it says this, which I had never noticed before "944 S: shut the safety pressure valve for crankcase breathing" - now that's interesting - anyone have a clue what or where this valve is? maybe that's part of the problem --- the search continues. > Perhaps you just have the wrong fuel pressure regulator on there. I > know that for the turbo cars, a performance chip set requires a [quoted text clipped - 5 lines] > Ah, I found the page: > http://www.lindseyracing.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=LR&Ca tegory_Code=944FUELREGULATOR SignaturePosted via a free Usenet account from http://www.teranews.com Don't forget the +/- 0.2 bar tolerance on the fuel pressure... That makes the idle pressure about 51.8 psi -- not far off from your measured 52... You also have some of your timing notations incorrect -- some of them should be BDC -bottom dead center. Intake valve closed after BDC because the momentum of the air flowing into the cylinder (due to its velocity) will contine to flow in, creating a slight positive pressure as the piston starts moving up. Also, I believe the valve timing is measured at a certain amount of lift (like 1mm), so the valves are still a little bit opened before and after those measurements. You're talking about what is PCV valve -- positive crankcase ventilation valve. On my turbo, it comes out the side of the oil fill housing and goes into the intake boot after the mass air flow sensor. This valve is to allow possitive pressure in the crankcase (primarily due to heat expansion) to escape. Because this air has oil fumes in it, it is diverted into the intake track to be combusted by the engine. You mentioned that you have PET, that should help you find its location. Going back to your fuel pressure -- if you hook a hand vacuum pump up to the pressure regulator (so you can give it a lot of vacuum) does the fuel pressure drop more than 52 psi? If not, then it would lead one to believe the engine is making adiquate vacuum. > ok, my daughter found the fuel pressure measurement I had made about 6 > months ago, at idle I had measured 52 pounds. [quoted text clipped - 27 lines] > > Ah, I found the page: > > http://www.lindseyracing.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=LR&Ca tegory_Code=944FUELREGULATOR p.s. I just put a vacuum gauge on my turbo (which is a very healthy car), and at idle, the vacuum it makes between 14 and 15 inches of mercury. Of course, when you blip the throttle, it instantaneously decreases a lot, and when you let the throttle body snap shut, the vacuum spikes up to about 18 in. Hg, then settles back to around 14.5. (If I put my finger over the end of the tester and pump it a few times, it goes up to almost 25 in. Hg.) It's interesting to note that the turbo's fuel pressure at idle is about 35 psi (2.4 bar), so it must have a larger injector to compensate for the lower pressure. I wonder what the N/A 8 valve cars have... I wonder if the injectors on your car were replaced, and if 8 vavle ones were used... > Don't forget the +/- 0.2 bar tolerance on the fuel pressure... That > makes the idle pressure about 51.8 psi -- not far off from your [quoted text clipped - 57 lines] > > -- > > Posted via a free Usenet account from http://www.teranews.com all good points - and with the car not here, it's hard to check out - I did check a lot of various things - I think hte PCV is a good guess - I didn't think there was a valve in there, but I'll have to look at it carefully the next time the car is home > p.s. I just put a vacuum gauge on my turbo (which is a very healthy > car), and at idle, the vacuum it makes between 14 and 15 inches of [quoted text clipped - 77 lines] >> > -- >> > Posted via a free Usenet account from http://www.teranews.com SignaturePosted via a free Usenet account from http://www.teranews.com > ok guys, this is getting silly. > Car = high mileage (225K) 87 944S. It's running rich. Fuel pressure is too [quoted text clipped - 10 lines] > replaced the o-ring on the dip stick and so on --- there has got to be some > reasonable explanation here, I don't want to just shotgun this This might fall under the "shotgunning" category, but won't a bad O2 sensor cause it to run rich? Bill, I know I've suggested this on past posts, but the best way I've found to find vaccuum leaks is a can of WD40. Since it's combustable, it works great to momentarily seal and pinpoint the leak. I also use it to clean and shine my engine. > ok guys, this is getting silly. > Car = high mileage (225K) 87 944S. It's running rich. Fuel pressure is [quoted text clipped - 11 lines] > so on --- there has got to be some reasonable explanation here, I don't > want to just shotgun this |
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