2000 XJ seems to run on 5 cy under 2100 when warm

Good Afternoon

This is kind of a long story so please bear with me. I want to give all of you the best information I can provide. I bought a 2000 XJ with a 4.0 with 239xxx miles on it. The person I bought it from experienced a cracked 330 head in the classic location, but stopped driving it right away( So he said ). I was able to start the XJ and drive it onto the trailer. All in all it ran very well, even though I did not run it long enough to let it warm up because of the coolant traces I could see in the oil.

Fast forward a couple of weeks, I have it running with a new head 7120 casting.. Found out that there was more bearing damage done that I had first thought. I pulled the entire engine out and tore it down for a rebuild.
Fast forward another couple weeks and I have it back from the machine shop, installed and ready to run. After I perform my 30 min -2000 rpm cam break in, I turn it off, check for leaks and change the oil, and filter. Now I am ready to drive it, and here is where my issue begins. When the jeep is cold it start up and goes through its high idle to about 1800 for 10 seconds or so, then settles in to a very smooth 800 rpm idle. I can then rev it and it seems to increase engine speed fairly smoothly, but with a slight hesitation right at the first move of the throttle plate. As the engine warms up I start to notice a change in the smoothness, it sounds like it’s not firing all 5. If you go to the rear of the jeep you can hear it in the exhaust note. It is loping on 5. If I slowly increase the throttle, right at 2100 rpm the engine jumps up 500 rpm, and get very smooth. The same is true one decal; if I hold it up around 2500 and slowly drop it to 2100 it will start to miss. Things I have checked.

• New Plugs-
• New and Verified CPS
• New and Verified Cam Sensor
• Verified TPS 5v


Tonight I plan to use my mechanics stethoscope and list to each injector when it is missing to see if they are all working when warm. Any ideas or direction would be greatly helpful. I have performed all this work myself, so I can follow directions, and know my way around my jeep. I hope I have included enough info to allow you all to weigh in.

Thanks !

Does a 2000 use a coil on plug set up? If so, I would suspect a bad coil that acts up when warm.
Only thing that comes to mind.
Hans

The 2000 uses a coil pack that mounts onto the plugs directly. When I say warm, I mean like after a 5 min warm up.

Not throwing a code? You can individually unplug injectors until you find the missing cylinder. Then swap the injector to a different cylinder. Best thing would be to check compression or cylinder leakdown.

Cris Engel said:

The 2000 uses a coil pack that mounts onto the plugs directly. When I say warm, I mean like after a 5 min warm up.

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coils fail warm.

I second the vote for a failed coil pack.

Good Afternoon


I thought it was time for a update. I had come to a place that it was no longer fun to try to figure this issue out, so I had to walk away for a while. I am back and ready to fix this beauty.

I have tested fuel rail pressure and swapped out coil packs. everything looks to be good. I came up with a bright idea to put my ECU into my buddy's 99 Cherokee. Low and behold the problem followed the ECU. It is not the same issues, but it ran really poorly,and shook. I'm convinced I have a bad ECU, and looking for a recommendation for a good place to buy one. is a refurbished ecu ok, or should i look at new only?


thanks again for all the help.

Cris

Moving the PCM to an earlier year shows nothing. 1999 and 2000 have a completely different ignition system.

What was replaced during the rebuild? I know you mentioned a cam breakin, but was teh cam or lifters replaced?

1800 for 10 seconds or so, then settles in to a very smooth 800 rpm idle.

Click to expand...

This is too high for a stock engine. Idle should be around 500 hot, and 1000 cold at most. I would start looking for a vacuum leak. Check the 90* elbow under the map sensor. Also, make sure the cam sensor is indexed correctly. Do not skip this step.

The Entire rotating mass is new in this engine. All stock OEM spec parts. I will need to look into the Cam sensor indexing. This is a step I did not do. I just pulled the old one out and installed the new one.

Nope, you need to index it. See page 5 here: http://jeep.blackonyx.net/pdfs/jcss.pdf

In short, bring cylinder #1 up to TDC on the compression stroke. Use a toothpick to align the sensor's reluctor ring with the hole in the drive body. Drop it in with the opening in the drive body pointing toward the back. Bolt it down.

Talyn


I just wanted to thank you for the information. This was the issue all along. I posted on a few other forums, and took a lot of advice for the gospel. Thank you for taking the time to help me..

Cris

Its 80% of the problems when a person does an engine swap.