2000 XJ 4.0L Popping / Sputtering Problem

[Talyn]

You might want to take a look at this thread. Particularly on the block interference: http://www.jeepstrokers.com/forum/viewtopic.php?f=34&t=2671

 

[5108696]

2000 Cherokee Sport / 4.0 L / Auto XMSN / 4 x 4 / 227k mi / Orig from NJ

I have had this Jeep for about six months. In the beginning I experienced a minor sputter every once in a while which I attributed to dirty fuel as it had been sitting a few months. I ran clean gas and a bottle of quality Sea foam fuel cleaner / additive. Obviously, that didn't fix it.
Early on, the problem could be described as an occasional sputtering, chugging, but without any popping or back firing. It normally lasted only a few minutes then went back to purring like a kitten with plenty of power on it's own. The check engine light also blinks during the sputtering period.
While I normally get 18 mpg, as the occurrence of the sputtering problem frequency increased, the mileage sometimes drops to 12 mpg...
More recently, the problem occurred like clockwork when I shut it off to fill up and restarted. It lasted only long enough for me to idle through the parking lot and stopped as I got back on the road. Thinking it may have something to do with the old, cruddy, fuel cap, I replaced it with the recommended unit from Auto Zone.
While there I had them read the codes. Nothing jumped out at me, but they mentioned (from memory) a random misfire on cyl #3, some sort of fuel line issue (vacuum issue?), etc.
I then checked all vacuum lines and fixed a couple of minor leaks due to deteriorated lines / fittings.
I should mention that the exhaust was rotted off from the Cat back when I got it and I replaced the rotted items with a turbo muffler, and a tailpipe. The problem was no different before / after.
Most recently, as the malfunction frequency continued to increase, and NOT go away on its own but rather continue as you drive, the following occurred....
I drove it on the highway for approx 40 miles. All ok. Oil pressure always reads max. Water temp was normal at 200*. Upon reaching my destination, I noted a bit more engine / valve-train noise than usual.
After it sat for several hours, I started it and the popping, pulsing through the gas pedal, back firing at an idle started (first time ever).
I checked the oil which was still clean and at the proper level, but I observed (first occurrence) nasty, flakey, carbon flakes on the dipstick above the oil level.
Having no other choice, I drove it home.
The backfiring stopped just above idle. It sputtered during acceleration, however once at speed, it smoothed out, but had a noticeable reduction in power. It ran ok at a steady 60-70 mph, but was weak going up hills.
Since then I checked the oil again – proper level, clean, and with no water. The coolant level was a bit below the proper level but not milky either.
The popping is really bad and I have stopped running it until I can figure out what is happening.
I thank you all in advance for your help.
Merry Christmas!
Rick

https://onedrive.live.com/?cid=9EF666F89D644D14&id=9EF666F89D644D14%213293&v=3

FINALLY, after all this time, I have solved the problems described above and throughout the thread.
First let me share my biggest regret... After initially planning to do a complete overhaul following the dreaded cracked head, at the recommendations of some associates who are professional mechanics, and based on no other problems than the crack, I got lazy and simply replaced the head. Since I had already pulled the engine and had it on a stand, I did change every component and sensor (timing chain and gears, pumps, etc. etc), unfortunately, I learned the hard way what a little coolant in the engine does for oil pressure...
Next time, no shortcuts.
I also scrapped the coil pack, replacing it with a Dodge Viper coil and wires. That was fairly simple and will make future troubleshooting easier.

After getting the entire job done and back on the road, I started experiencing another missing episode. Whenever it was idling - be it in park, or at a stoplight in gear, it would get this miss like you were grounding a couple of plug wires which would totally dissapear when you raised the idle by a mere 100-200 RPM.
When it started happening more often, specifically while cruising at very low RPM, I started researching it again. Suspecting the Idle position thingamajig wasn't doing its thing, I loosened the two screws, started the engine and monkeyed with the adjustment. While there was really no range of adjustment to speak of, while holding it to one stop it ran crappy, and a sixteenth of an inch the other way smoothed out. After tightening it back down there, it has purred like a kitten with not a single sputter since. It is hard to believe that this whole (latest) missing delimma was solved with a 1/16" adjustment of the thingamajig....

I hope after all of this trial and error I have gone through that someone will read my thread and get some insight to help with their own similar issues.

A huge thank you to all of those who took the time to post info and recommendations to my many questions. N A X J A Rocks!!

 

[truckeejeeper]

Excellent thread. I missed the idle position thingamajing info though, what/where was that exactly? The TPS? Not sure what you mean. Same problem here. thx-

 

[truckeejeeper]

Try cleaning the little sensor in the manifold next to the throttle body. I think it's the IAT? Unscrew it and go at it with some throttle body cleaner and a toothbrush. I did mine and took ALL the yips out of my 4.0. Easy, worth a try-