92 oldsmobile 88 stalling when cold fine when warmed up - Page 7 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-24-2006, 09:35 AM   #61
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Excellent work guys.
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Old 03-24-2006, 09:59 AM   #62
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Quote:
Originally Posted by 88 Coupe
Quote:
Originally Posted by bill buttermore
........ if I remember how PCV valves work, they are calibrated to be pretty much closed at high vacuum, then open up as load increases and vacuum falls ........ the leak (wherever it is) is dropping the vacuum in the manifold and allowing the PCV valve to open up, putting the crankase under a light vacuum, which sucks in air and throws off the idle when you open the cap ........
The statement is incorrect. At idle, vacuum holds the PCV open, not closed. Willwren is right in thinking the comp is compensating for an improper mixture, but it'* actually leaning a rich one.
Geez, I hope I didn't screw this up (but, if I did it wouldn't be the first time!) I may be incorrect,as you say, but here is the reason for my confusion. The '92 FSM says this: " To maintain idle quality, the PCV valve restricts the flow when intake manifold vacuum is high. If abnormal operating conditions arise, the sysem is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent tube into the throttle body to be consumed by normal combustion."

And I am thinking vacuum is pretty high at idle, so the valve may not be completely closed, but should not be wide open, either.

I read about the mis calibration elsewhere, I'll see if I can find that source.

Anyway, I think you and Willwren may still be right about the PCM re-learning idle, and it is certainly worth a shot to check out the PCV fresh air passages.

I do not pretend to understand this fully, but I am working on it.
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Old 03-24-2006, 11:10 AM   #63
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OK, found something else that may explain this problem. While Googling "pcv valve operation" (where I read that the PCV valve in a closed system like we have here is nearly closed at idle) I ran across this tip:

"unplug the vacuum hose to the charcoal canister - if you feel vacuum at idle, the purge valve is bad"

What they are saying here is that the purge valve should be closed at idle, not allowing vacuum to suck in vapors from the fuel tank.

Now, I'm not sure that this is gonna apply, but it is worth a shot. Although the FSM says that purge operation is possible at idle, it should not happen when the car is cold. Anyway, when the car is cold, find the hose that goes to the charcoal vapor canister - remove it from the vacuum source - and plug the vacuum source. Start the car. If the idle is smooth, reattach the hose to the vacuum source - if the idle gets crummy, either the purge valve is bad or the vacuum line to the canister is bad or you have a vacuum leak somewhere in the canister system. Won't cost you anything to check this out.

BTW, this is also listed in the diagnostic chart posted earlier.
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Old 03-25-2006, 05:27 AM   #64
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Hello everyone,

Quote:
Originally Posted by bill buttermore
........ I am thinking vacuum is pretty high at idle, so the valve may not be completely closed, but should not be wide open, either ........
Your reasoning is sound and my simplification was oversimplified.

I'll be watching to see how it comes out.

Regards, Norm
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Old 03-25-2006, 01:41 PM   #65
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Believe it or not had my friends brother check it out he took it yesterday hooked it up to vaccum guages and everything. and it turned out to be the o2 sensor that i replaced 2 months before the problem started happening. Weird because none of the symptoms were for an o2 sensor. But im happy its all fixed now. Now its on to do brake pads calipers and rotors today.

thanks for your help everyone.
Jason
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Old 03-25-2006, 02:01 PM   #66
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also if anyone ever has this problem i found something else that might be helpful in the diagnosis.


Also, run the car then take off the oil cap or the dipstick, does it run the same? If so then you probably hve a vacuum leak as there is supposed to be vacuum, when you take that off its opening up the vacuum lines therefor making it run like ****.

not sure if this is true or what but hopefully it could help someone.
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Old 03-25-2006, 07:13 PM   #67
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Glad to hear you got it fixed. But I can't quite put the symptoms with the fix

Quote:
Originally Posted by 92olds88royale
...run the car then take off the oil cap or the dipstick, does it run the same? If so then you probably hve a vacuum leak as there is supposed to be vacuum...
That would imply that there is a vacuum leak in my '95, and it surely doesn't act like it. From what I have observed and read, in a closed PCV system like we have, there should be no noticeable vacuum at a crankcase opening (like you could feel with your hand over the hole) when you open the crankcase with the engine idling. Recall, we tested this effect by asking others to test idle with the filler cap off and on. (Maybe no one else tried it?) At least with my '95, it made no difference in the idle at all, and there might have been a very small vacuum, but not that I could detect with my hand over the filler hole. I suppose there could be something wrong with my '95, but it seems to idle and run pretty well. Maybe someone can enlighten me, or it will just have to remain a mystery.

Anyway, I am glad you got it running right. You were very patient and persistent and sometimes that'* just what it takes.

All'* well that ends well!
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Old 03-26-2006, 08:01 PM   #68
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i believe once the computer went into closed loop mode once it started to warm up thats where it started using the o2 sensor and it was reading wrong (crappy 15$ standard sensor) because it wouldnt cause the problem right away. My guess is that the o2 sensor was reading wrong and making the car take in too much air because of the inacurate reading. Because after i changed it and i pulled the oil filler cap off it wasnt doing it anymore. Weirdest thing ive ever seen yet.

thanks for all your help everyone bill youve been extremely helpful with this

jason
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Old 03-26-2006, 08:20 PM   #69
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Thanks for letting us know how it all turned out. Sorry we didn't recommend the O2 sensor for you earlier. I'll file this info away for future reference!
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Old 03-26-2006, 09:22 PM   #70
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hey dont worry about it im just happy i found the problem. i would never think the o2 sensor would do that but hey i guess cars do some funny things sometimes.
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