I have a 1991 xj and it started a while ago that at certain rpm's at low speed(around 2000) I get the bad vibration. I had somebody hit the throttle while I was underneath and realized the exhaust shakes bad at that rpm range. Any idea what it could be?

 

Unbalanced driveshaft?

 

Ya think the driveshaft was spinning while he was under there?

 

hahaha good one. That made my morning

 

Errrrrr...

Sounds like maybe your exhaust hangers and engine/transmission mounts have seen better days.

 

 

I have brand new poly brown dog motor mounts but I didn't do tranny mount like I should have

 

Did it start about the same time you replaced the motor mounts?

 

No it started before I changed them. They were stock ones before and they were destroyed! But the vibrations made me think that was the problem so I changed them. No difference. Then I thought it could be my badly cracked exhaust manifold so I swapped that yesterday and it made it a little better (less vibrations) but they are still there

 

Animated.... LOL

 

So if you jeep guys read his mother ****ing post, he has 2 different issues. One being vibration at low speed, and broke exhaust. I was replying to his vibration issue

 

Exhaust shaking is caused by the vibration

 

Ahh. That would be in order!

The tricky thing about XJs is that the exhaust is completely rigid. So if your engine is allowed to flop around, then yes any resonance will cause the whole thing to shake. This is why the manifolds crack.

 

From what you say the engine isn't running smoothly, like a miss or something that causes the vibration? I'm grasping at straws here trying to find where its at before a fix can be found.

 

It runs good as hell. It's just at 2000 rpm this vibration goes through the whole rig. Whether it's standing still or moving