Bad running Cherokee, can you help me?

[semper fi]

I have had a problem with my 2001 Jeep Cherokee when it had it's old engine, and now the same with the new one.

It appears to be getting worse. It will idle badly sometimes and others it will idle fine. It runs good and others it feels like it has lost at least half of it's power and if you floor it it won't move any faster.

If the gas pedal stays in the same position it doesn't get any better. that will last for about 30 seconds to a minute, then it goes away and will run fine. Sometimes it will come to the next stop light or stop sign and will not idle correctly or it will.

I have replaced many things trying to solve this problem over the last year to year and 1/2. I have a new engine, a new spark plug/coil wire setup(what ever it is called),throttle body and sensors, and have dumped a lot of fuel injector cleaner in it also.

do you have an idea what I could do, or what is wrong with my Jeep? I have spent a lot on this Jeep trying to restore it to 100% and I want it to run like it did before. Thanks for the help and thought you may have given my problem.

[4.3LXJ]

Changed O2 sensors lately?

[cantab27]

you say ya swapped out engine.....maybe electrical.. check all earths on truck ,cables ....you fellas will have different names for that me thinks.....cats not blocked up is it???...have you wheeled it hard or is it a dd...

[Mudderoy]

I have had a problem with my 2001 Jeep Cherokee when it had it's old engine, and now the same with the new one.

It appears to be getting worse. It will idle badly sometimes and others it will idle fine. It runs good and others it feels like it has lost at least half of it's power and if you floor it it won't move any faster.

If the gas pedal stays in the same position it doesn't get any better. that will last for about 30 seconds to a minute, then it goes away and will run fine. Sometimes it will come to the next stop light or stop sign and will not idle correctly or it will.

I have replaced many things trying to solve this problem over the last year to year and 1/2. I have a new engine, a new spark plug/coil wire setup(what ever it is called),throttle body and sensors, and have dumped a lot of fuel injector cleaner in it also.

do you have an idea what I could do, or what is wrong with my Jeep? I have spent a lot on this Jeep trying to restore it to 100% and I want it to run like it did before. Thanks for the help and thought you may have given my problem.

Check the fuel pressure on the rail. Also check to see how long it hold pressure with the engine off. If the harness is sitting on the fuel rail at the back of the engine, use a nylon tie wrap and get it up and off that fuel rail. It will actually wear a hole and then wear into one of the wires going the the ECU causing it to act funny.

[semper fi]

CAT is not blocked up, O2 sensors have been replaced, and it has been wheeled good. I have yet to check the fuel pressure.

[belvedere]

Here are some thoughts, in no particular order: TPS, vacuum leak, test fuel pressure, check/clean grounds, any codes?

[Cheromaniac]

The first step is to have your ECU scanned for fault codes. Autozone will do it for free. It'll help you pinpoint the source of the problem rather than continue throwing parts at it in the hope that you might get lucky.
If any engine sensor reads out of range, it'll throw a fault code that's stored in the ECU's memory. Sometimes it can be the sensor itself that's at fault but often the sensor will detect a different problem (either electrical or mechanical).
Let us know which fault codes you find and we'll take it from there.
Can someone give me a few rep points to bump my score up a bit? ;)

[straightsixjeep]

Here are some thoughts, in no particular order: TPS, vacuum leak, test fuel pressure, check/clean grounds, any codes?

X2

[semper fi]

I know it has been a long time since I have posted on here but, my Jeep is now fixed and is running great again! There were some small problems with the jeep such as the motor mounts, that I was told were brand new were not, needed to be replaced.

The bad motor mounts allowed the engine, which you could not feel, shake bad enough that it effected the knock sensor. The sensor tryed to adjust the engine and that caused a problem.

We replaced the motor mounts thinking it would fix the problem, it did not.

There were several other small problems that gave us "a big problem" that we fixed.We replaced every sensor you can think of, wow the cost! Even after we got all of the small things fixed, which could be wrong with your jeep and not cause anything, it still ran like shxt. We had been working with a dealership and one of the "tecs" said he wanted a look at it. The first thing he asked was "have you timed the new engine since you have put it in?" My mechanic friend said " yes of course I did". The Tec then asked if he used a computer, and my friend did not. The next thing he said, and did, floored us both. The tec told us that my jeep, 2001 Jeep Cherokee, has to be timed with a computer. All other Jeep Cherokees older than mine, 2000 and back didn't need to be timed on a computer. We both thought this guy was full of shxt! We gave him the keys, and after being on the computer for 2 days, it runs like a brand new Jeep!! He put it through all types of test to include a warm start and a cold one. It runs great! He told me that very few people, the do an engine swap, will tell you that it needs to be timed on a computer. He did tell me that mine was 30 degrees out of time. I was amazed that it even ran!!

I just thought that I would pass this along to all of you just in case you may be having problems that you can not figure out.