Chasing low throttle misfire - Any suggestions?

**BlackGS** · 09-26-2012

I'm getting misfires on cylinder #2, but only when the throttle position is less than 5% (light cruising, idle, park, etc.). Any throttle over 5% and the misfires are gone. This started about 2 weeks ago right after I switched back to 93 gas from e85. I really don't think the switch back caused the problem - just a coincidence, but I thought I would mention it. When I'm cruising, the misfire count gets high enough that the TCC unlocks, so that is annoying, and I'd like to get this resolved. Any suggestions are appreciated.

Here is what I have done so far:

Swapped plugs - misfire stays on #2
Swapped plug wires - misfire stays on #2
Swapped coil packs - misfire stays on #2
Swapped injectors - misfire stays on #2

Cam is stock with 1.9 roller rockers and 105# springs. Spark plug in #2 looked great, and all plugs looked exactly the same. Car pulls very strong with no hesitation.

**BillBoost37** · 09-26-2012

Do you have an ICM you can swap out?

**BlackGS** · 09-26-2012

Originally Posted by BillBoost37

Do you have an ICM you can swap out?

I do not. I guess I could at least check all the connections to the ICM.

**gtpsleeper** · 09-26-2012

hows your tune look?

**BlackGS** · 09-26-2012

Originally Posted by gtpsleeper

hows your tune look?

Tune is very good. I run open loop, but it is interesting that when I tried closed loop, the misfires seemed to get a bit worse. Since fueling in closed loop is more erratic with the up and down cycles, I can see how that could compound the problem.

**BillBoost37** · 09-26-2012

Not sure I understand how tune could make one cylinder misfire unless you skewed that one injector heavily in one direction.

**BlackGS** · 09-26-2012

Originally Posted by BillBoost37

Not sure I understand how tune could make one cylinder misfire unless you skewed that one injector heavily in one direction.

I agree. Tune might make the misfire count higher or lower in that one cylinder, but would not be the root cause. I have my front bank skewed very slightly higher, but that has been like that for years.

**gtpsleeper** · 09-28-2012

Originally Posted by BillBoost37

Not sure I understand how tune could make one cylinder misfire unless you skewed that one injector heavily in one direction.

because I notice in my OL tune that if I ever go too lean or have a random lean spike my #2 is always the one that misfires... why? cuz its a grand prix... thats the reason I ask...