Weird rough running
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1st Gear
Joined: Oct 2022
Posts: 1
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Weird rough running
My 1990 L98 Corvette has about 52000 original miles although I have not owned it for more than a few years. It has been super strong running, the fastest L98 I have driven but the engine looks stock. Anyway, my problem: it runs like it has 1 or 2 non-firing cylinders and the idle fluctuates. But, to me there is a big tip off but I don't know what it means. For 15 to 30 seconds after starting it, it runs on all 8 cylinders. Then it quickly goes to crap. That seems to be electronic to me, There are no codes. The system says all is good. I have changed the coil and the ignition control module with no change. I cleaned the throttle body and the idle air control valve. There are many things that can cause rough running but the fact it runs on all 8 when starting up puzzles me. I have listened to all injectors after it's warm and they all sound ok. Ideas are strongly welcomed. Thanks in advance.
Melting Slicks
Joined: Sep 2010
Posts: 2,422
Likes: 202
My 1990 L98 Corvette has about 52000 original miles although I have not owned it for more than a few years. It has been super strong running, the fastest L98 I have driven but the engine looks stock. Anyway, my problem: it runs like it has 1 or 2 non-firing cylinders and the idle fluctuates. But, to me there is a big tip off but I don't know what it means. For 15 to 30 seconds after starting it, it runs on all 8 cylinders. Then it quickly goes to crap. That seems to be electronic to me, There are no codes. The system says all is good. I have changed the coil and the ignition control module with no change. I cleaned the throttle body and the idle air control valve. There are many things that can cause rough running but the fact it runs on all 8 when starting up puzzles me. I have listened to all injectors after it's warm and they all sound ok. Ideas are strongly welcomed. Thanks in advance.
bad ICM typically equals NO spark.
Cap & rotor, Plugs, gap, wire condition?
Need to connect a fuel pressure gauge on the rail
Validated pressure. 43 -45 Idle.
I personally validate all pump stages.
Listening to injector pulse. Only tells you. Its pulsating.
Ohm out every Injector. The average should be very close or exact.
Ps. Incredibly LOW mileage.
