Jeep bucking wildly

breadbutcher

New Member
Joined
Dec 23, 2022
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8
Location
Georgia
Hey folks! 2001 manual TJ 6 cylinder wildly bucking around 2k rpms in 1-3, sometimes in 4th. The bucking is nice and violent, happens multiple times in a row, and the rpms tank. The problem doesn't happen all the time. I took it to a mechanic and (of course) he is having a hard time getting the problem to occur. He thinks a new PCM would fix the issue but that seems a bit expensive to throw at it. Any ideas I can tell him to look at before I bite the bullet and order a new PCM myself? Also, any reputable online places you would recommend getting a PCM from would be great.
 
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I'm not sure what it is but that doesn't sound like a PCM problem. It sounds like it could be a timing problem which usually leads to a defective crankshaft position sensor. So far as a reputable source of PCMs, there is one that is excellent, www.wranglerfix.com and if you get to the point of calling them, ask for Mark who is an active member of this forum. Mark @Wrangler fix does this sound like it could be caused by the PCM?
 
If it's doing that when you accelerate hard, and feels like you are bouncing off a rev limiter, it's probably the fuel pump. Check your fuel pressure.

No codes, I assume?
 
@JKP When it happens I'm not pushing the pedal to the floor but it happens when I accelerate and when I am at a cruising speed (more at acceleration though). No codes.
 
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@breadbutcher I think your bucking issue is a rev limiter caused by the Jeep being out of time. I have enclosed a picture that shows the timing mark alignment.

5002F01D-7FF3-407C-81A8-4CBCDA54CDCA.jpeg
 
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I just have to ask...
Are you sure there are no codes? Does the check engine light come on with the ignition on but not cranking? Sometimes those bulbs burn out or are removed. I have had the bucking with a crank sensor code. I clear it and it's gone. This only happens when the battery goes dead or is replaced, for some odd reason.
 
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It did a while ago but not since. And I can't remember what the issue was, but it had something to do with an emissions system that comes directly off of the engine block. Tracing the issue I found the unit in question had most of its tubing cut off and electrical tape covering some of the holes. It didn't seem to bother anything at the time so I wrote it off.
 
Update! So the Jeep is back home. The mechanic ultimately did not find anything wrong. The camshaft sensor and timing was great, the fuel pump was working correctly, and the only thing he could think of was the PCM and he did a shake test with no results. He also made sure that all of the grounds and power were good to go on those wires. It hasn't bucked once since coming home and the only theory I have is that somehow (maybe?) the PCM was messing up somehow but it was reset somehow (possibly?). I have no clue. Anyway, thank you all for the suggestions! Just glad to have it back.
 
Mine did the same thing with a bad camshaft position sensor caused by (or in combination with) a bad OPDA.

Yep. The connector or sensor. I have been battling bucking due to a loose crankshaft position sensor. Does exhaust smell like rich carburetor?
 
I had similar issues and replaced the crankshaft position sensor. All was good for a while then it started again. Put the original back in and all was good. I’m guessing since the sensor itself wasn’t the issue it must have been the electrical connection.
 
I had similar issues and replaced the crankshaft position sensor. All was good for a while then it started again. Put the original back in and all was good. I’m guessing since the sensor itself wasn’t the issue it must have been the electrical connection.

I have the old one back on too and the connector zip tied. Issue is that a wire at the back shell broke on th engine harness side. Bought an aftermarket and spliced it in. But not a good fit. Need to find a better harnesses side connector. Junk yards here I come.