: misfires @ idle & WOT, no codes



mechanix
06-25-05, 04:57 PM
I need some input, gentlemen! This has been an on-going problem since I bought the car. At present, mileage is 66K.

SYMPTOMS: The engine misfires at idle whether in gear or not. Not a rhythmic miss that is consistent with RPM, but more like a random misfire. It has stalled the engine a few times. And at WOT it hesitates and misfires very noticably. There is no surging at cruising speed, and it runs smooth as glass in all rpm ranges and loads, except for the aforementioned.

WHAT I'VE DONE SO FAR: New fuel filter, NAPA plug wires, AC Platinum spark plugs, NAPA FPR, AC air filter, head gaskets and bigserts, milled heads .008", complete valve grind. The compression is 185# on all cyls., I have tested both primary and secondary circuits on all the coil packs as per the service manual, and cleaned out the throttle body. I've been all through the vacuum system checking vacuum readings, hose condition, etc. I have also been through all the wiring harnesses, cleaning and checking connections and grounds, taping, routing and covering wires, etc.

The only code I am getting is for a trans. position sw. that is slightly out of adjustment and unrelated to my problem. Since I am getting no relative DTC's, I am down to a "buy it and try it" mode of parts replacement. What is the next logical step? Crank sensors? I have run a search for threads on this problem and I've come up empty. Thanks!

JimD
06-25-05, 05:21 PM
Put a stethoscope on each ignition coil at idle. You will be listening for an internal arcing noise that coincides with the miss condition.

Internal breakdown of the coil insulation could be random and temperature sensitive.

No cost testing!!

eldorado1
06-25-05, 07:19 PM
Have you gone through several tanks of gas since it started to eliminate that potential cause?

mechanix
06-25-05, 10:29 PM
Thanks, JimD. I will try that. I'm not sure what you are asking, eldorado1. I have been through several tanks of fuel for sure, and the problem has always been there. Nothing I have done to the engine has improved this problem any, except that maybe it doesn't stall the engine now, but it still acts like it wants to. The really peculiar thing that has me stumped is that it only shows up under no-load and full-load conditions. In between it runs great. Go figure! *lol* My gut instinct says it is ignition-related. It just feels like it.