Hi all.
I have a 1993 Cherokee 4.0 with 233000 on the clock. When it idles for 2-3 min it sounds like it's a misfire, and after 5 min it will start to smoke a bit. If you give it some gas or drive it, this goes away. I have replaced wires plugs cap and rotor to no avail. The motor shakes at idle and it is driving me nuts! The wires are a chepo set from O-riley’s and I have no faith in them. I’m going to do an Ohm check on the wires tonight when I get home. Any help will be appreciated Thanks!!!

 

With 230k and some smoking, I think I would perform a compression test on all cylinders. A good snapshot in time of the condition of the engine.

Easy to do, perform a dry test and if any cylinders read low, perform a wet test (adding a teaspoon of oil to see if compression increases)

The compression spec. for the Jeep 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.