Many thanks to Sentinal02. This thread made it very easy for me (a novice) to test everything and determine the computer was bad. I am going to take it out tonight and send it out to get it repaired. But thanks again for the very detailed diagnostic writeup!
I have read a lot of things about replacing the capacitors for the ECU, is there anyone on here that has successfully completed this with the 4.0L? I have the same symptoms, and am hoping that this will fix it. Thanks!
"If the ladies don't find you handsome, they should at least find you handy" -Red Green
I just went through the tests and found that I'm getting about 5V across the "Dome" fuse terminals. I'm getting fuel to the fuel rail, but I'm not getting any spark. When I turn my key to ON, the CEL never comes on (confirmed bulb works). Could this be the ignition switch like you said, and it is getting enough power to prime the fuel pump, but not enough to give spark? I'm going to test the ignition switch wires tomorrow, but it is too late tonight.
Another Huge THANK YOU for this thread. I have a 95 2.5L 5 speed and it died the other night. It would start occasionaly for about 15 sec then die and not restart. I checked the fuel, did a complete tune up (knowing it MUST be the cap or button). No good. Then I found this thread and determined that the CEL was not coming on so I hoped it was the ECM. After a $6 trip to Radio Shack and about an hour replacing the caps, the CEL came on and she started right up time after time.
I am also wondering about this working on the 4.0. I tried replacing the capacitors, and my symptoms remain. I'm afraid I have missed a step, or was hoping this would be a cure-all, and of course, that's not the case. I have a 91 with the 4.0. very slow to start, temperature doesn't matter, CEL works. I was thinking of the CPS as being the culprit, but hate to "replace parts till its fixed". I would rather know why it's happening so we can help others with this problem.
If your CEL lamp comes on when the ignition is first switched on, then the capacitors in the ecm are not your problem. Yes, this covers the 4.0Ls as well, the ecm caps and related symptoms are the same between the 2.5L and 4.0L. Check for codes, if the cps is at fault, it should throw a code. If no codes, check your fuel pressure at the rail. Start a new post with your symptoms and what has been done to date so others can help you figure out what is wrong.
Hey, I'm a first time visitor to this forum and hit a grand slam on the first try. My '94 Wrangler wouldn't start. I followed this diagnostic proceedure to the letter and low and behold my computer was bad. Since I have some electronic background I decided to try to repair it. It was the best $4.14 I ever spent at Radio Shack. One question I have is, how critical is the "jelly" that encases the internals of the computer? Is it for shock absorbtion or waterproofing or what? I scraped a lot of it off of the top side of the circuit board looking for screws that would be holding the board in the case only to find there were none. A gentle pull with a springhook under the edge of the board and it popped right out. Anyway, I just put some RTV around the base of each capacitor to help support them and put it back together. Fired right up. AWESOME!!!!! Thanks again