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1992 GMC S15 Jimmy, engine will seem like its missing and lagging

I have a 1992 GMC Jimmy with the Vortec 4.3L V6 with the CPI (central port injection) fuel induction system i know the spider injector harness has a tendency to fail but i've noticed that the engine runs extremely rich and has many driveability problems

my perticular problem isn't with the spider injector harness but how the engine will miss, lag, and not rev to over 2500 - 3000 when it does it it also back fires through the intake or sounds like its back fireing through the intake manifold............... heres the catch though it doesn't do it on a constant basis it will run fine for a few days have lots of power like it should but then it does all that it seems like the engine has a blown head gasket at its worst point but there is no coolant in the engine oil and nor an external head gasket leak the truck doesn't leak any thing

also if it helps the engine has approx. 191,247 miles on it and does not burn any oil at all i've noticed that the intake manifold is full of oil sludge but how would a bad PCV valve cause thisit passes the Indiana air emissions test i also know that the EGR valve is bad but it passes emissions with flying colors and the "SES" light has only come on twice both times on the way home from Kankeekee i shut the truck off for any where from 30 seconds to 5 minutes and it runs better not great but there is a considerable diffrence then the running condition deteriorates again after a few minutes it also will heitate and bog when starting out from a dead stop i've replaced a few vaccum lines with have helped had to do some rerouting of the vacuum lines which has helped but some times it still runs horrible it has me stumped

this whole ordeal has me dumb founded any help that would contribute to the remedy to my problem will help greatly

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  • Anonymous Jul 06, 2008

    yea s10 vortec 4.3l vaccum leakes and miss fires do work together. me 2000 is doing the same but i changes vaccum lines and pcv valve, truck ran better asap but some times i hear suction release after i turn truck off. but the vaccum is the first thing my budy at shop asked me!.


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Have the EGR valve checked. My son-in-law has a 4.3 Vortec Blazer. It had similar problems. Had to replace the EGR valve. Rumor has it that these engines tend to foul that valve, making it inoperable. Hope this helps!

Posted on Jun 14, 2008

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