I just leased a new 2007 Grand Cherokee with a Hemi and immediately found the vehicle to have a harsh vibration when traveling at highway speeds that only occurs when using the accelerator. The vibration stops immediately when removing your foot from the gas pedal and coasts at highway speeds. The dealer advised the vehicle is operating within normal limits. This is not possible. There appears to be something wrong in the drive line, e.g., drive shaft, differential, transmission. I have read that others have had this problem on other forums but no real answers. Does anyone have any idea of the cause of the problem. I am having it checked out by another dealer on Monday.
Ask them to let you drive an identical model. If it is normal that one will do it too.
Hemi’s have displacement on demand. When coasting, the computer shuts down four of the eight cylinders to save on fuel. If the computer is working properly, this changeover from four to eight cylinders should be fairly seemless.
The dealership needs to check this system out. As the other poster suggests, drive another Hemi to see if the vibration is there…
I will drive another cherokee this weekend. The service dept advised that they drove another cherokee with a hemi and it exhibited the same vibration. If this a problem that occurs in all these vehicles shouldn’t it be resolved by Jeep/Chrysler?
Can’t be driveshaft, differential etc. as you suggest since they don’t change with throttle position. Coasting doesn’t change the balance of the driveshaft, for example.
You’ve got a driveability issue, something engine related. I’d suspect a simple plug, plug wire or coil pack problem.
It could be the tires if they look like mudders.
When it does this, have you tried giving it more gas? It maybe that the variable displacement is staying in the 4 cylinder mode because you aren’t “goosing” it enough.