Ok, this has officially stumped me. Here's the story...

About 3 years ago, I noticed one or more of my cylinders were missing at idle. This happened right after running some seafoam through the vacuum line on the brake booster. I took it to several shops and they all had a different diagnosis.

1 . My spark plugs were no good...

-My problem with this diagnosis is that the plugs were only 3 months old (were replaced after it started missing) and were Bosch Platinums. He changed the plugs out for Autolites, and the engine ran better, but still not quite right.

2. Timing appeared to be off...

-Had the timing set professionally and put in brand new distributor (I'm not sure what they call it on the 2001s, but I only know it's where the distributor would go) and cap. No change.

3. Crank Position Sensor was bad...

-This seemed the most plausible cause, however one day my Jeep failed to start. Took it to the shop and they replaced the CPS and it fired right up. However, it's still missing... After firing it up, I had them check the compression of the cylinders... seemed one cylinder was pretty low when first starting, then pressure climbed to 95lbs after a few seconds. Which leads me to believe oil is getting in between something and sealing up the cylinder. Possibly the piston rings?

Another thought I had was maybe the valves need reseated or replaced. Also was thinking about replacing the head gasket or even getting a brand new head with valves already in place.

This is something that's been going on for almost 4 years. And I'm afraid to drop $400 for a head assembly to find out it's not the problem. Also, replacing pistons and rings is something that I have not done myself yet. But I'm not afraid to try and tackle it if I need to.

The only other option I've thought about is just getting a new 4.0 longblock and putting the exterior components I have onto it and go from there. But $2000 is money I don't currently have. Trying to fix the problem rather than work around it.

I would appreciate any ideas or advice!

 

If it's a '96-'98, there is a TSB that says to replace the valve springs and use Mopar Combustion Chamber Cleaner. It fixed a persistent cyl 1 misfire on mine.

 

Mines a 2001. However, that doesn't sound like a bad idea. I also just heard that the 2000-2001 engines are having issues with heads cracking? It missfires intermittently on cylinders 2, 3, and 5 if I remember correctly.

 

Sorry, I was in a hurry and overlooked the year. Hopefully someone will chime in with more on the cracked head issue.