1996 Jeep Grand Cherokee Random Stalling Solved!
 

First post here, and I would like to explain my problem as well as the solution in case anyone else with a 90's ZJ experiences these awful, terrifying symptoms.


I have a completely stock 1996 JGC 4.0 auto trans with 243k miles. Runs great (prior to issue) and is my daily driver. Starting several months ago in December it would die or almost die very randomly. I could be at a stoplight, or driving 70mph. The engine could be hot, cold, or in between. It progressively became worse but never left me stranded long term. Sometimes the motor would start right back up, sometimes it would take several minutes of waiting or cranking. Pretty scary when it dies on the mountain highways where i live in CO and there is no shoulder or it happens on a blind curve. A little backstory here, but i had a 1994 toyota 4runner once that had a random stalling problem very eerily similar. After testing, guessing, and replacing nearly every dang possible part on that yota, a friend of mine and great Jeep Mechanic found a loose ground wire way behind the firewall that went to many things including the fuel injectors. We tightened it, and i drove that 4runner another 100k. I learned some hard lessons there and was determined not to throw parts at my beloved Jeep like i had years ago with that 4runner. I researched a bunch online, including a bunch of past forum posts trying to find some folks that had similar Jeeps and symptoms. As many of you know, thats a rabbit hole in and of itself, but i got lucky. Without other people posting their problems and solutions, i NEVER would have figured this out, and i would have rebuilt the Jeep part by part and spent a small fortune chasing a ghost.


So i started up the Jeep and started checking grounds and jiggling wires. When i wiggled the grey ECU wire harness behind the coolant overflow reservoir, i got the Jeep to stall. I then did a google search and found a person with the same ZJ that had the same problems, and he figured out that the ECU cover mount screws (1/2 inch long torx screws directly underneath the ECU wire harness connections) were causing a short. Reading further, some others with the same problem either backed those 2 screws out halfway, replaced them with 1/4 inch screws, or cut the screws in half which is what i did with my dremel. Once i did this, i could no longer wiggle the grey wire harness and replicate the stalling. Problem solved! Test drives have all been great. This problem was at the point that it was no longer safe to drive the Jeep, and i hope if anyone else with a 90's ZJ 4.0 has that problem, they find this post and try this very quick fix before going down "Replacement Road".