northline76

I have a 2001 Cherokee Sport, 4.0l. The engine is a reman that has less then 20,000 miles on it so far. I have also put a bored throttle body and the upgraded neon injectors on it.

The issue that I have been having since June is a rough idle, slight hesitation, slight power loss, and every once in a while I will give a random misfire on cylinders 1 and 6. This all started out of the blue, I had finished putting a new water pump on and on the test drive it had random misfired bad enough to have the check engine light flashing at me. At times the rough idle is bad, bad enough that I can hear the dead miss in the exhaust and it rocks the jeep at idle, other times it is not nearly as bad you can barely tell theres an issue. It idles at a steady level, it doesnt do anything crazy.

I have changed the spark plugs 3 times with none of them looking bad or having a tell tale sign of an issue. The whole coil pack has been replaced. The injectors were all rebuilt in may and have been check out. New TPS, new CPS, new O2 sensors, New Cam positon sensor. I have checked the wiring for shorts, I found two exposed wires for O2 sensors and repaired that. Otherwise no other shorts have been found. I havent found any vaccum leaks either.

I have had it looked at by a dealer tech, and then brought it into the dealership and he checked all the electronics on the computer, no issues. According to the dealership computer all sensors are functioning properly and that it is a perfectly running 4.0l. I also did a compression test and got a range of 130-140, which is good for all cylinders.

So at this point I am completely clueless as to what could be causing this issue. Electronics all check out fine, verified by the dealership, compression check came back good, nothing to indicate an internal problem. The only two things I could think it could be would either be the mini cats are bad and have a slight blockage, or the computer is bad. Any ideas on what it could be would be great.

Slick761

I'd check out those injectors again.

413maxwedge

Look at the injectors for your year

02tj

sounds like a bad pental in a injector.

northline76

Yes I got the 784s, and the caps were all replaced. I even switched back to stock injectors for a while and it made no difference, the problem was still there.

02tj

possable cracked ring? burnt valve? leaking intake gasket?

northline76

I doubt its a cracked ring or a burnt valve, its a new engine with less the. 20k on it. Plus all those problems would be magnified under load and would have shown up with the compression test. Regular driving there is no sign of a misfire or any other problems. I plan on getting new mini cats and will redo the gasket then. This is the most difficult problem I've ever dealt with and several mechanics I know have no clue how to fix it.

02tj

Is it a ATK or Jasper motor, an on a side note I just noticed your in Gloucester Va. I grew up in Glenns Va and went to Glo-high.

XJeepWerks

Subscribed because I have the same problem.

02tj

Cam Postion Sensor in the dizy will do it to, low fuel psi, bad crank postion sensor, bad fuel, leak in exhaust manifold or intake manifold, slow up stream 02 will do it. actually need to see it in person w/ a scan tool cappable of grafting streaming readings will pinpoint issue.

413maxwedge

No dist. on a 2000-01, 02tj,Since you have replaced just about everything that would cause your issue, about all you have left is to check for the right fuel pressure (49psi steady i believe)or a possible clogged filter on pump lucky the filter can be changed without removing the whole pump assembly, and the filter and regulator are part of the same piece on top of the assembly.( just make sure you have about a 1/4 tank or less of gas.Just keep an eye on the two orings if you only see one when removing, the other is still in the hole.(if this is your problem)A couple more things it could be is carbon biuld up on a valve ,not letting it close. But your engine is basically new so I don't know about that but you never know. your plugs are gapped correctly right ,and the boots and springs are on right too?

northline76

Yes fuel pressure is the one thing left to really check, I'm gona rent a gauge from advance and check it Monday. I have seafoamed it at least 3 times, it helped for a short bit but it has always gone back to the same symptoms. Spark plugs have been gapped correctly, I always double check em before I put em in. They are sitting at .035 Boots are on good too. I want to try getting a noid light and actually testing each injector while its running to make sure they are working properly. My worst fear is that there is a tiny short in the wiring harness that is going to take hours to track down.

JerseyTrueBlue

Any update on this? Dealing with the same problem on cylinders 3 and 5 for a few months now.

northline76

No updates so far, talked to 02TJ and he feels it may be a small internal issue. He thinks he'd be able to find it with a scope, id just have to get to him. Right now making the three hour drive just isn't in the schedual for me. I haven't had any major issues with this so far so I'm just going to run it for now.

JerseyTrueBlue

Damn I'm stuck in the same position of dealing with it because I can't find out whats wrong. Changed/tested everything I could so far with no results.