run your hand along the plug wires while the engine is running,,, if you get shocked your wires are leaking, lol. try looking under the hood in the dark with engine running. if you have sparks flying the wires are leaking. to misfire i would think the spark is jumping from one wire to the other. odd that its at a certain rpm. spark should jump with no consistency.

 

I'm sorry it sounds like it's coming out the engine not the exhaust

 

does it occur only when cold (open loop) or only when warm (closed loop) or C: all of the above?

still awaiting a reply about year engine, year ECU

since it has an aftermakret cam and no egr, who provided the tune? What has data logging shown you, your fuel trim, O2 readings (do you have them)
knock count etc

what octane fuel are you using?

even today, I still use a vacuum gauge. I baseline my cars when they are running well

what do you know of the engine that you purchased

who did the work to install it?

 

Hot or cold and it does not have a tune should it have one only thing I did was the hypertech programmer that's it

 

is the engine used or rebuilt? being it has a aftermarket cam, who set the lifters? when and how?

 

Used rebuilt my pops set the lifters he knows his way around engines

 

3rd time asking these questions

what year engine?

what year ECU is in the car?

what sensors were discarded?

what sensors were kept?

what year transmission?

 

Engine is out of a 94 ecu out of the car it's a 95 Z28 just the ones that went to the original manifold and the pump in the drivers side it's a T56 that was in the car sorry for the late response and appreciate the advice