94 LT1 developes missfire when warm
11-02-2011, 11:55 PM
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94 LT1 developes missfire when warm Hi,
I've been slowly working through the brokenness of the car I bought, and it starts up and runs fine now. However, when warm (driving for 10-15 minutes), it will start to misfire/skip when I accelerate. The check engine light will come on, however once I've turned off the car, and I come back the next day the light is off and it runs fine for the next 10-15 minutes. Is there any way to scan it so see what the code is saying since its not OBD-II? Anyone have an idea of where to start? I've run seafoam through the car and that cleared up some backfiring issues, but apparently not the misfiring issue. The car was stored for 6 years before I bought it so take that into account too. Thanks
I've been slowly working through the brokenness of the car I bought, and it starts up and runs fine now. However, when warm (driving for 10-15 minutes), it will start to misfire/skip when I accelerate. The check engine light will come on, however once I've turned off the car, and I come back the next day the light is off and it runs fine for the next 10-15 minutes. Is there any way to scan it so see what the code is saying since its not OBD-II? Anyone have an idea of where to start? I've run seafoam through the car and that cleared up some backfiring issues, but apparently not the misfiring issue. The car was stored for 6 years before I bought it so take that into account too. Thanks
11-03-2011, 07:54 PM
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i had the same issues just recently, i would first check for vacuum leaks...the if thats good i would check the plugs, if they are black and sooty, replace them with new, and then check your O2 sensors, if they are black and sooty then you can try to clean them but its best to replace them. i changed out my cap and rotor on my opti spark because it had some carbon tracing on the contacts. as far as the ICM, get some washers and space it off the side of the heads to allow air flow between the Icm and head. i replaced all of the listed components and now it runs like a raped ape! good luck
11-04-2011, 03:31 PM
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yes definitely scan it
my experiences with hot ICM or coil is the car just shutting off and it will not start until it cools off.
10-15 minutes should not be enough time to cause that but it would be enough time for the PCM to go into closed loop so you might have bad O2 sensors. wouldnt hurt to run a fuel pressure gauge while it is happening. if it starts turning into voilent backfires and sputtering then you could be sufering from hi-res fail on the opti.
my experiences with hot ICM or coil is the car just shutting off and it will not start until it cools off.
10-15 minutes should not be enough time to cause that but it would be enough time for the PCM to go into closed loop so you might have bad O2 sensors. wouldnt hurt to run a fuel pressure gauge while it is happening. if it starts turning into voilent backfires and sputtering then you could be sufering from hi-res fail on the opti.
11-04-2011, 07:26 PM
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If the car is shuttering or feels like its missing ( worse when in low rpms ) Mine did the same it was my O2 sensors . If the car sat that long i would suggest atleast changing the fuel filter also .
11-06-2011, 11:34 AM
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I suggest checking fuel pressure, my car has very similar symptons, when I start it up it would run fine for 10 minutes or so, and then begin to crap out. Checked my fuel pressure when first started, found it was about 40 psi, when misfiring it would settle to about 35 psi, and if I held the revs up it would lower down to 30 psi at about 3000 rpm. Spec is 42-47psi with a 5 psi spike when removing the vacuum hose for the fuel pressure regulator. Quick and easy while not requiring the replacement of parts to check.
