Problem in drivetrain

Ok, in the last week my XJ's developed some kind of a problem somewhere in the drivetrain. It's a '95 XJ with 147,7xx miles on it, and I have to sheepishly admit that though it's been a DD, paved surface-only car, I've DOGGED it hard a LOT.

So, anyway, sometime last week I experienced my Jeep doing SOMEthing that I would assume is the transmission slipping. Thurs/Fri is when it first did it. It was slight and subtle, and I can't really remember exactly what it felt like. However, I did also notice when I had my window down that during heavy acceleration, I could hear this dull popping, thumping sound like something was constantly going through the binding/freeing itself cycle coming from under me from the drivetrain.

Then I didn't feel a THING in it driving it twice for about 40 minutes each that Saturday.

Fastforward to yesterday and today. You know how when you're in 4hi or just have it strung out in the RPM range and you let off the gas, there's a jerk as the slack is taken out of the drivetrain and then compression braking commences? Well, Monday, just cruising down the highway very sedately at a constant 65mph, I experienced THAT feeling. Only a bit worse. And sometimes it would do it once. Sometimes about 4 - 7 times in a row, back to back, all within about 10 - 12 seconds.

It did the same thing on the way to school today. Fearing it was the transmission slipping, it suddenly dawned on me that it MIGHT be the torque converter slipping or locking/unlocking erratically. However, it then proceeded to do it in the city going a constant 40mph. During that ~25min commute it probably did it 27 - 33 times.

So, to recap, since this is a rather long post:
I had this binding sound under acceleration ONE day that I've not heard since (though I don't think I've had my window down since then).
Then it's gotten so it jerks at a constant speed, and it's done it from 40mph to 65mph, and the vehicle's temperature has no influence on it.

Dad just drove it tonight and says it's not the transmission, really doesn't think it's the engine, but suspects it's the transfer case. The transmission has never given trouble before, still shifts just fine, and, while being worn from my constant aggressive driving style, the engine uses hardly any oil and runs good.

Oh, and the transmission fluid is up to level, clean, and smells just fine.


Thank you SO MUCH for reading through such a long post.

What do you think it could be?

Sounds like a miss to me.

That's what Dad said it sounded like, but the engine seems to be running just fine. He's fairly confident in ruling that out.

Ok, I think you're probably right, now.

This morning on the way to school, it was acting up and doing the same thing, only not quite as pronounced, just barely rolling in a line of stop and go traffic at a stop sign. And then it did it with my foot off the gas, on the brake, sitting still just idling. So, it's GOT to be the engine.

When I get home I'm going to clean the battery posts, as they're corroded a little. If that doesn't do it, what else should I look into?

Thanks!

Sounds like a stretched transfer case drive chain to me. Pretty common espescially with hard acceleration driving.

Buy a TPS, try it, then take it back if it's not it.

Ok, well I have an update.

It most definitely is the engine misfiring. By Saturday the problem had gotten MUCH worse. Dad drove it and said at least two cylinders just weren't firing at all. So, we took the spark plugs out to check them, and they weren't gunked up, oily, wet with gas, or anything else. But we had already bought new ones so we went ahead and put them in. We also ended up replacing the battery because decided to die on us right before we started checking the compression.

I don't know what the firing order on the 4.0 is, so I'm just gonna list them from front to back. The first cylinder had by far the lowest compression.

1: 110
2:130
3: 125
4: 135
5: 135
6: 135

So, the good news here is that the compression is IDENTICAL to what it was when we last checked it three years ago. Which is incredible to me (and all my friends) because of how hard I am on this thing.

Anyhoo, we drove it after installin the new spark plugs, thought it was fixed. But then it started doing it again, but it was the much more subtle misfiring that it originally started exhibiting.

Last night after it was dark I cranked it up and looked under the hood, and three spark plugs and the distributor are arcing all over the place. So hopefully Dad picked up some new wires today while I'm at school/work, and we'll install them tonight.

Here's hoping that'll fix it!

wow, if you got open arcing, you definately need some wires!

Wow! That's all I can say! I just installed the new spark plug wires and took it to fill her up at the gas station, and it's a night and day difference!!!

I'm really blown away. I had no CLUE spark plug wires could make such a difference! I can actually coast smoothly to a stop. And sitting at a stop light once I had to check the tach to make sure it was still running. And she pulls so strong now, too.

I'm stoked!


Oh, and any comments about the compression readings we got? In case you missed them, here they are again:

1: 110
2: 130
3: 125
4: 135
5: 135
6: 135