Project: 2002 GT Track Only Kar

[Steve85]

Thats about 8" from the manifold so about 1 foot from the heads.

I was thinking timing but it only happened on one bank (passenger, not drivers side) and to effect individual cylinder timing isn't easy in these motors, and didn't change the global timing at all. I don't have long tube headers, just stock manifolds. I'm really starting to think it's a plug not firing and the spent gas is being pushed into the exhaust and the cat is catching it and trying to burn it, with a cylinders worth of gas coming every few seconds it would make sense.

I agree, if it's only in one bank, prolly not timing.

Do you have one of those infra-red thermometers? They are great for finding the misfires, especially in fords where the center exhaust ports aren't tied together. Point and shoot at the manifolds the misfirng cylinder will read 100+ degrees cooler.