Hello everyone. I have a 1991 jeep cherokee 4.0 automatic.

And when I start her up I get bad vibrations like something hitting underneath my jeep with a hammer. And it doesint do it while its cranking, only right when it starts. Then once it gets to normal idle it quits. And I don't know if this has anything to do with it.. but more towards the back of my motor there is a "roaring" sound.... anyway, I would like to thank everyone in advance.

 

Got a tiger in your tank? You might check that your header/downpipe or exhaust is bumping something....

 

Its definitly more vibration then the exhaust. The whole jeep moves, I don't know what it is! I did tighten the motor mounts a little bit.

 

So it sounds normal cranking, then it idles smooth, but between there it bucks and bangs so much the whole jeep shakes. Any chance that roaring sound is from a pipe, or air moving, sucking? Just on GP you might want to remove that little inspection cover on the bell housing and check your torque converter to torque plate bolts. They are known to get loose and bang like a hammer down there. As long as you are there you might want to check some engine to bell housing bolts.

 

Alrighty, ill do that in a hour or two and ill get back to you. Thanks!

 

Mine does that when I start it in 4WD, but not when I start it in 2WD. No idea why.

 

Id say something with your transfer case.. or maybe you front driveshaft.. check how much wiggle room it has?