O.k. here is the issue.....
Car: 96z28
symtom: after car warms up car begins to misfire getting progressivly worse until car stalls. Scanner shows Short term fuel trim for bank 2 going from+- 1% 125 to +18% 145 and this increases until car stalls out. Bank 1 stays normal. This can be repeated over and over again after car cools down.
DTC Codes: P0300 (engine misfire) P1361(Ignition Control (IC) circuit high voltage (shorted or grounded circuit))
clear codes and they go away until cycle starts over again.
Attemped fixes: Replaced leaking water pump and opti at same time, swapped coil and ICM, replaced plug wires.

Any help would be much appreciated Thanks

 

did you replace the plugs too? although I think it would still run with a fouled plug- just extremely rough.

 

oh yeah, maybe an injector issue as well?

 

Sorry I forgot to mention the plugs are pretty new less that 10k miles. When the car 1st starts the engine runs perfectly usually around the 10 minute mark is when the mis starts mild at 1st, then growing progressivly worse until engine shuts down. I think the injector trim increase and increase in pulse are a result of the miss. The injectors can't see the unspent fuel from the lack of combustion but can pick the extra oxygen and intepret that as a lean condition thus the pcm starts to increase fuel starting the downward trend to eventual stalling. Would you agree with this assesment?

 

A cold start car doesn't use the O2 sensors to control air/fuel mixture. They kick in after the engine is warmed up. How old are your O2 sensors? Do you have any exhaust manifold leaks that could be affecting your O2 sensors? Bad O2 sensors or exhaust leaks will screw up your air fule ratio. Also check to see that your coolant temp sensor that provides input to your PCM (the one located in the waterpump, not the driver's side head that goes to the temp gauge) is within proper working range.

 

Your warming symptom is indicative of a problem O2/circuit as mentioned above. You may need to change the plugs on the right side as they may now be misfiring. Scan it and see what the right front O2 reads when it warms up, if you haven't already. Then disconnect the right front O2 which forces it to run in open loop and see if it runs better even after it's warm. Scan it again. If the reading went from lean to about 450, then you know the O2 is bad. If the reading stays lean, then you know the wiring is shorted.

Since you were running so rich, it's almost a given the O2 is shot. Be sure if you replace it that you check the plugs since any fouled plugs will only cause damage to the new O2.

I wouldn't be concerned about the other codes until you address this problem. The 300 is probably from fouling plugs causing them to misfire.

 

Thanks you for your suggestions, I'm going to try them now. The car is usually in closed loop mode for about 5 minutes before the misfiring starts, but I like the idea of keeping it in open loop to see how this effects the car.

 

Any updates on this? Thanks!