HELP....92 4.3 CPFI Probs! - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-28-2001, 09:51 AM
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HELP....92 4.3 CPFI Probs!

Hey guys,
Im still trying to figure this problem out and getting very frustrated in the process! I have a 92 GMC Jimmy with the 4.3 Vortec CPFI fuel injected motor (W-code).
I am having a running and starting prob with it.This is a problem that developed overnight and not a case were it was getting worse and worse.
When the motor is cold it starts up fairly well. As it warms up it starts to run rough.It almost sounds like its running on 3 cyls.It is VERY bad on gas now to. When the motor is hot it is vey hard to start.....I have to open up the throttle all the way and let it clear out. It is not setting any codes on the computer, this was checked by myself on the check engine light procedure and by a local mechanic on his scanner.I have replaced the plugs with Rapidfires improvement. Also Cap and rotor were improvement. I put my timing light (Snap-on) on it to check spark in each cyl.....good spark and proper advance in each cyl. Even pulled each wire to check spark and running cond....spark was GREAT, jumped at least 3/4" and I did notice a small change in running cond when each was pulled, almost sounded like an intake backfire.
With the advise of a good GM tech, I replaced the entire CPFI injection unit inside the plenum. $400......OUCH! He said it was VERY common relacement and GM has had alot of probs with it.......NO CHANGE!!!!!!
The local mech mentioned it was "dumping fuel" on one side of the engine before I relaced the CPFI unit.....I cant see how as it is only 1 injector for the whole system and is then routed to each cyl through small fuel lines with a poppit valve at the end of each. The fuel pump was replaced not to long ago so I cant see how that could be it but it sounds like its possible??? I was also thinking it may be the O2 sensor but I cant find one anywhere. Cant find one on the manifolds or on the head pipes!
Sorry for the long winded post but I am hoping someone here may know this motor well enough to help me out a bit.....needless to say I am getting very frustrated....and sick of pouring money into this for parts it doesnt need!
Thanks for any insite on this guys.........Herbie

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post #2 of (permalink) Old 04-28-2001, 09:43 PM
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Re: HELP....92 4.3 CPFI Probs!

Kinda sounds similar to a problem I have had twice before. In my case it was a sticking EGR valve due to carbon fouling. It happened to me about 2 years ago, and also just last week as I was driving from CA to TX. The symptoms were lousy mileage, very rough idle, and a funny smell coming from the exhaust.

The frst time it happened, A GM mechanic just removed the EGR valve and cleaned it. Everything went back to normal. This last time, I just sprayed 1/2 a can or carb cleaner down the intake and after driving a couple of miles, it cleared up. Hope this helps.

93 S-10 4DR Blazer Tahoe 4X4, 5" suspension lift, 33X10.50 BFG AT's, 'glass front fenders.
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