I have a 2000 cherokee I bought two months ago. It drives good at highway speed but acted up on me a few times when stuck in heavy traffic. The motor would feel like it was starting to flood out and start missing. I could put in N and rev the motor a few times and it would be ok. I took it out wheeling for the first time and it was missing really bad at low rpm's at first it would clear with engine reving but evetually go so bad it shut down. It will start 30 min later and runs fine for a while then starts loading up again and will shut down in about 45 min. As soon as you get it back on the highway it runs fine for the ride home. I have changed the spark plugs, coil bar, and put insulator on injector 3. When I have code read it usually reads cylinder 3 misfire but will sometimes read mutilple cylinder misfires. What should i do next?

 

I ran it around the house today - left it idle for about an hour while doing work, moved it around a few times - no problems - I don't get it.

 

Man couple of things, check your fuel pressure, maybe the regulator has gone bad, also you ecu ecm, which ever you call it the computer, maybe going out. I would start with the fuel pressure and go from there.

 

What kind of pressure gauge do you use. All i have is an air guage.

 

goto your local box auto parts place and rent a fuel pressure tester, and get a haynes chilton or some kinda manual, it will walk you thru it how to use the tester and all, plus you get your money back after you take it back. let us know what the reading is.

 

Error Codes?
Sounds like a Heat Soak issue.

 

That was my line of thinking also Frank. Sounds every bit like that may be the problem.

 

Code is usually cly 3 misfire. After wheeling when it was really bad I had a misfire code for each of the 6 cylinders. I put the insulator on injector 3 this past weekend - it has been running better on hot starts but still acts up when driven really slow off road.

I wanted to do a compression test but an not familiar with the coil on plug set up. Do I need to unplug the coil bar and ground anything or do you just leave the coil bar plugged in and pull it off the plugs and set it aside during the test - I dont want to mess up the coil bar. I've only ever had distributor set ups before.

I'm also going to try to check the fuel pressure when I get a chance.

 

my 97 did that and it ended up being the Throtle body position sencer replaced and fixed

 

link don't work

 

check the IAC

 

I had a problem with multiple misfires when I first got my 96 4.0 and over the next several months my ignition lock cylinder was going bad and finally did. Once i swapped it out and put the new one in the check engine light went off and no more misfires!

 

Hmmmmm...weird.
Just go to the Search page and type in HEAT SOAK.

 

It sounds like Heat soak! Like FrankZ said

As far as i know, It happens when the exhaust heat gets a little to hot. The fuel injectors sit between the exhaust and intake manifolds. The excess of heat creates air bubbles in the fuel injector. Thus causing it to miss. This is also why it runs fine after you hit the pedal a couple times.

They made a recall for it a couple years ago I think. They added a little heat sheild between the manifolds and the injectors. Mine still does it all the time.

 

I had a dodge truck that did the same thing turns out there was a wire going to the injectors grounding out causing a misfire this could also cause it to go away unexpectedly