I have a 88 cherokee, the engine is from a '91 comanchee, I rebuilt it awhile back and put a very mild comp cam in it, and a mega squirt fully sequential (MS3X), I decided to do the intake swap from a '99 and put a bit more aggressive cam in. I had the head resurfaced (the third time, up to .030" shorter than stock) the block is bored to .030" over, and I used a .041" MLS head gasket. I have IAT's that climb very rapidly, as if fire was shooting into the intake. I have a loud clatter as if a lifter on cyl #5 failed, which goes away when the coil (coil near plug) and injector are pulled from that cylinder. The engine runs rough, and backfires like mad if the throttle is moved.

 

Sounds like a possible timing problem. Is it timed correctly, whether it is the distributer or the timing chain?

 

I have pulled the timing cover and double checked cam timing , and crossed checked it against the napa chain I had on before. The thing about the distributor is that all I'm using it for is the cam sensor/trigger, but I don't have anything solid to go by for where to put it, the old cam was obviously much less sensitive because I had no issues with it. The mega squirt is fully sequential, and by that I mean I have sequential injection and six coils-not using the distributor for timing, the ecu has direct drive for each coil.

We are going to double check the TDC damper assumption, and make sure there's no hydraulic lifter preload due to increased compression ratios taken straight off the piston to head clearance.

 

Possible valve problem. Could be pre-detonation.

 

Some of both, which was my thoughts too, got it completely apart and found the damn gremlin, intake lifter for the #5 cylinder has been destroyed, the cam wore through it until it had a hole in the bottom of it, and the cam lobe is also destroyed, looks like there was lifter seize-up on start up, in spite of my extreme care in installation and prelubrication.
So it'll be another set of lifters, and another cam, $200 cha-ching.