sporadic misfire at cruise

[ericm]

I have a stock '91 GST. The last few months it will sometimes misfire when I'm at cruise (low throttle opening). The engine starts and runs fine. The misfire only happens when the engine is up to temperature. A couple times the engine has died. It restarts readily. It's lit the CEL a few times. The code is 44- bad coil. I have not been able to get anything interesting with the PocketLogger. The misfire happens about every other drive to work (35 miles). It never misfires under boost or at idle.

So far I have replaced the plugs (NGK BR6ES), wires, and coil.

One thing I noticed with the logger is that at low throttle openings the O2 voltage swings back and forth. Reading the FAQ (thank you FAQ maintainers) that sounds normal... is it?

Looking through old threads I see lots of different possible solutions and a depressing number of posts with variations on "well I replaced X and that didn't do it either".

I think my next steps are to replace the power transistor, CAS, and look at the ECU. Is that correct? Any other ideas or new wisdom?

Thanks!

 

[Defiant]

Have you gotten the coil CEL since swapping?

 

[pooker]

You might want to try testing your front o2 sensor.

 

[chrish1440]

You might want to try testing your front o2 sensor.

I had the same problem, and it was due to the O2 going bad

 

[ericm]

Have you gotten the coil CEL since swapping?

Yep. I'll try the O2 sensor, thanks.