space between head and ICM/coil

[Craig 94 TA GT]

I finally tried putting a few washers between the ICM/coil bracket and head. So now there's a 1/4" gap between the two. Well, the car runs a lot better. I had a miserable low end stumble/hesitation that kept coming back, but this really seemed to help. I should have measured before and after temps. But, so far, it's seemed to help quite a bit. It doesn't make sense, though, how some LT1s are plagued with this problem, and others aren't...especially when there is no space in stock configuration. Has anyone else here tried this and had good results?

[TraceZ]

Ya know, I've always intended to do this but never got around to it. I'll take this moment to go do it. Hang on.....

......

......

......


.....


Ok, the deed is done. I'll let you know if it is smoother next time I take it out. Thanks for the reminder.

[Craig 94 TA GT]

Cool, I'm excited to know your results. Did you have a low end hesitation before? I did (and slightly do sometimes but nowhere near as before). Whenever I would hit the gas more than 1/4 down from a dead stop, it would hesitate pretty badly. However, I do have an exhaust leak that's causing one bank to run richer. My BLMs are at 140/128, and I don't know if that has more to do with the hesitation or not

[TraceZ]

Cool, I'm excited to know your results. Did you have a low end hesitation before? I did (and slightly do sometimes but nowhere near as before). Whenever I would hit the gas more than 1/4 down from a dead stop, it would hesitate pretty badly. However, I do have an exhaust leak that's causing one bank to run richer. My BLMs are at 140/128, and I don't know if that has more to do with the hesitation or not

I've never had a hesitation problem, bit it does seem to run smoother when cold. I'm hoping it runs smooth all the time now.

[dochidalgo]

Craig:
I have read about this issue that the ICM is cooled by the engine cool fluid when it circulate thru the head, so it seems that mod you already done will not help so much to cool the ICM. I have wanted to do the mod but I haven't found a real base to perform it.
Hope TraceZ could give us a real base to think it worth
Take care
Dochidalgo

[Sean 94z28]

Craig,

Just curious if your stumble was only occuring after the engine warmed up. Meaning, in both open and closed loop mode.

Sean

[TraceZ]

I took it for a little drive, It does run a bit smoother now. Maybe this is a sign I need a new coil or ICM? Maybe my coil/ICM is sensitive to heat? I'll have to keep an eye on it.

[Craig 94 TA GT]

Sean, the hesitation only occurs in closed loop, or when the engine is warmed up. That could mean 1 of 2 things...
1) when it's taking in readings from the O2s in closed loop, the exhaust leak is hurting the reading(s) and causing the problem. A leak would cause it to think it's running lean, thus richening the mixture. Maybe that's why I'm getting 11.5 MPG on city driving
2) when the coolant heats up to roughly 200 degrees, the ICM and coil do not like the heat...and break down. I'm not sure what the ICM consists of, but I don't think out PCs or any circuitry would last or perform at 200+ degrees.

But so far, the hesitation is way down, and it's running much smoother, just as Tracy's Z. I ordered new headers/y-pipe/cat, which will be installed in a few weeks. I'll keep my results posted if this entirely gets rid of the stumble/hesitation once and for all.