Grand Cherokee [“ZJ”] Project

Click on boxes below to view different phases of the build.

Components needed:

New/remanned/used factory computer. Can be found in wrecking yards, online on sites like Ebay and others, or from the dealer for various price ranges.

Socket wrenches, dielectric grease

30 minutes to 1 hour of time

Process:

The reason we decided to replace the computer (PCM) was to address a really random stalling problem that the Jeep had for quite some time. After replacing numerous sensors under the hood (IAC, Crank-Position Sensor, and TPS) and not fixing the problem, we decided to give the computer a try. The first re-manned computer we got from the dealer was for the wrong engine (the 4.0L), and the second computer had an issue with the voltage regulator, which we found out AFTER replacing the alternator. Finally, we got to our third computer and fixed a few wires in the wiring loom and we fixed our problem. All of this can be seen in Part 3 of our video series on Youtube.

STEP 1 - Remove coolant overflow tank: The computer is tucked up against the firewall on the passenger side of the Jeep. Use a socket wrench to remove the coolant overflow tank to allow access to the computer.

STEP 3 - Swap out new computer: Place the new computer into place. Use the three bolts to secure the computer back to the firewall. Use dielectric grease on the plug and plug into the computer. Tighten the bolt that holds in the plug.

STEP 4 - Inspect wire loom (if needed): This isn't a necessary step, but will help to make sure everything is in good order. There is a lot going on in the loom and it is a mess to take apart (see right). We found a few wires that were potentially problematic, but added some electrical tape on exposed areas to prevent any shorting out.