Cylinder 4 Misfire
 

Long time lurker, first time poster. I've searched for this problem on the forum already and have came across a couple that are similar to mine but not quite the same. During start up I'll randomly get a cylinder 4 misfire code, I can feel it missing but as soon as I take off there is no sputtering or any problems with it missing afterwards. HPFP holds well (1900+) and there is no unusual knock. The car has the following mods:

-Autotech HPFP internals
-RMM
-Test pipe
-3 in intake
-50/50 E85 tune

I swapped the cylinder 4 coil with cylinder 1, problem still happens. Spark plugs are all gapped at .026. I've heard the seals can go out on the injectors but before I get into all that I would like to know if anyone has had a problematic misfire before.

Got any logs to post?

I don't have any logs I can post right now (work computer), I'll post some tonight.

I'm in the same boat as you and I've pretty much narrowed it down to the injector. If you've already swapped the coil and the spark plug to another cylinder and it still persists on cyl 4, do a compression test.

Also wouldn't hurt to run a can of Sea Foam through the gas tank either. It helped me keep the misfire away for like 2 weeks. Now it does it again but less frequently. Check your coil packs and their harnesses too for any corrosion or anything like that.

Swap the plugs, as suggested. Just to make sure. It's not happening at WOT? Just start up?

Cold startup? Does it happen if you do a warm startup? (hold the gas slightly while turning the engine over then release)