Cyl 1 misfire

PCDJ64

MEMBER
1997 BUICK LESABRE
127,000 MILES

The trouble with my buick lesbre is never ending, no hope in sight.
had a mechanic tell me I had a bad ICM because the car does not start hot, it keeps shutting off unless you hold the gas for a minute, after that it is fine well ALMOST.
i replaced the ICM, crank and cam sensors, coils, bosh ultra premium wires and irridium plugs. Also a new fuel pump, filter and pressure regulator on the fuel rail. New upper intake with the upgraded EGR tube and gaskets from the dealer.
as of right now it still does not start after it is hot, it is misfiring on cylinder 1 even after replacing all of the parts I listed, only misfires if I hit passing gear on the highway or up a steep hill, you don't even feel the misfirw but the check engine light goes on the second it is under a load. The fuel pressure is fine, once in a while it sounds like it misses a little at an idle but the light does not go on. Seems to have lots of power, also tested for vacuum leaks and found none. Throttle body has new sensors and is shiny like brand new, no carbon at all. The air charge temp sensor is new too. Sensors are replaced over time not all at once. Car just had a brand new exhaust installed along with 2 new O2 sensors.
the car does not need a CASE relearn, again was told by mechanic.

8 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

I would start with basics. A compression test on cylinder 1 is in order. I would check the injector for being clogged. Not adding cleaner in the tank, a professional cleaning.

You need to verify the injector is firing with a good ground from the pcm.

I would look at all basics before throwing all those parts at it with no result.

Roy

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Monday, May 28th, 2012 AT 9:53 PM

PCDJ64

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127 POSTS

123 or 124 PSI on cyl 1, seems that the miss has cleared up, even up hill under load it did not throw a code.
Further testing for the issue of not starting properly when hot.
If I try as soon as I shut it off it will start back up no problem, and it will for up to about 5 or 10 min, after that it shuts right off unless I hold the gas part way for a few seconds, after I let the gas go it idles great and runs good. Fuel pressure issue has been ruled out, car has a complete new ignition. The only original sensor is the knock sensor. No vacuum leaks or any type of fluid leaks or loss of any fluids, no check engine light, engine is very quiet and smooth with new ignition compared to the way it was.
I hope it is not PCM, seems to me all of the basics have been covered unless I am missing something, the fuel injectors are bosh and in great shape.

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Tuesday, May 29th, 2012 AT 6:53 PM

PCDJ64

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127 POSTS

First I want to thank you for the replies and the help.
The issue is resolved with the misfire and failure to start up when hot, the car had a faulty lower intake manifold gasket which probably should have been changed when I replaced the upper intake manifold.
One final question, how many knock sensors does the 3800 series 2 have? I found the one near the oil filter, I used it to drain the anti freeze from the block. I was told that they have 2 of them but I only see the one.

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