I read that misfires on these 4.0's are pretty common,but mine is a bit differnt than a #3 misfire when hot like most I read about,this is all 6 all the time.I just bought this 96 4.0 217xxx grand Cherokee limited for $500,witch is a great deal cause its in really nice shape.BUT the engine missed the whole 2hr trip home,from being cold all the way up to running temp,so i took it to the oriellys today and every cly threw a random misfire code.The previous owner (not very smart) replaced the plugs and wires,ive gapped them,cleaned the throttle body,replaced both 02 sensors and changed the coil,any ideas?she cuts out from the time it starts till u shut it off,so i know heat soak isnt the problem,thanks

 

Don't the HOs have a camshaft sensor that can cause this? I'm not sure because I have a Renix Maybe even dirty connections?

 

Which plugs are in there and how large a gap?

I don't know much about the ZJ Grand Cherokee. No idea if it's OBD-II or where the MAP is. Any other symptoms like hard starting, rich running? You might try in the Grand Cherokee forum section.

 

im not sure exactly on the brand or number but the gap is at .35

 

My Cherokee would idle like crap and would die out if I gave it gas. Turns out my IAC motor (idle air control) was shot and it wasn't moving. Check that. Sometimes they just need to be cleaned

 

Your problem is very simple. You bought a Grand Cherokee and not a XJ!!! Sorry, I couldn't resist.
Wish I knew more about them to help you out. Not real familiar with the GC. But that's just because I really not a fan of them. Just my preference. Welcome to the forum and good luck on your repairs.

 

It's a '96 4.0?
Look for something common to all 6 cylinders. Coil connections, CPS, engine and body grounds, PCM connectors...
Vacuum gauge- check for sticky or floating valves caused by weak springs. (unstable vac reading at steady 2000-3000 rpm)
Compression check wet and dry wouldn't hurt either.