Hoping for some guidance, my trial and error has left me almost broke. I have a 95 Cherokee sport 4.0 liter Auto trans, 4x4. I picked it up with a blown head gasket. Repaired that and drove it for a few days and started running hot again, Drove it into the shop, my barn actually, lol, and started looking into the problem. After visually inspecting for leaks, i tryed to start it back up after setting for a week or so, and it has no fire or fuel pressure. I am getting 12 to the coil when i turn on key, it will turn over, and i am not getting any fuel rail prime from the pump. I jumpered the fuel pump relay, and the pump is operating. I also noticed while attempting to pull the codes, that my check engine light isnt working. i replaced the bulb with a new one, actually tested it 2 times prior to installing it, and still no light. I pulled the under dash and column cover off and discovered the ignition switch, which are different in 1995, has a burnt spot on it and the wires had gotten hot as well. further diagnosing led me to the PCM and found a burnt circuit strip on the board itself. It was the 4th pin, depending on how you look at it, which is the BLK W/LT BLUE stripe. this wire runs to almost all of the sensors and connects to the PCM pin that contained the burnt strip on the board. I realize i need a new PCM, but my question is this, what should i do to reassure myself that when i install the new PCM that it wont just fry as well? Can i test the IGN switch, im lost as to what to do next. I also replaced the CPS as well. Can anyone give me a start in the right direction without "trying to replace" parts and see if it works? Thank you in advance. Dyin in Phx.

 

Not really info, but in the time that your wiating for your new PCM go back and doubled check all fuses, relays, connections, and mainly all your grounds.. You said your removed the head and repaired/replace the head gasket.. And after so she was running.. but over heating.. As for the over heating i would start will the thermostat.. conitnue with water pump and then radiator.. did u bleed the coolant of air pockets?

As for the no start not pressure at the rail.. thats probably your pcm we cant diagnose much until you have that in..

Now when you reinstalled the head, did you mount the engine to firewall ground?? It looks like a breaded steel shoelace. Some people tend to over look that and will cause shorts in a few places.. But like i siad before these are just things to check out while you wait for the new pcm.. CHeck the burnt wire under the dash and see where the goes, inspecting for any open wires..

 

Thx for the quick response. I went to a few wrecking yards yesterday but couldn't hook up with a PCM yet, but did manage to afford a used ignition switch, (the burnt wire under dash), A partial fuel rail/sensor wiring harness and a coil, all for $15. I thought that replacing the partial harness as opposed to just the BLK w/LT BLUE stripe wire made a little more sense and will probably be easier too. I did recheck all fuses and relays, all fuses tested good, and i switched the AC relay around with the Auto Shut down relay but no diff. AC worked when last driven. I am assuming that the A.S.R. is a regular relay, nothing that needs to be specifically an AutoShutdown. I did drive it a few days after the top end gasket kit and unfortunately it is a possible hairline crack in block. keeping fingers crossed hoping its not. I did replace the Tstat as well as the hoses. The CPS was what i thought going to be my cure all, but not the problem. Is there any way to prevent toasting the new PCM, or is it even possible to toast it if i just hook it up and try it? I wanted to figure out why this happened to it before i installed another one, or was it the PCM that simply failed? I will let you know what happens later today and i really appreciate the help out there. I am going to install the ign switch and as much of the harness i picked up as possible. PCM is supposed to be available today, and i think that it is a MUST HAVE anyways due to the Check engine light not operating at all any more. Am I on the right track with that theory? I dont want you to think that your professional advice is not being utilized as well as appreciated, because it is very much so. Thanking you again, Maybe running today if all goes well!! then i will deal with the Overheating. Let me know if you think i should go a different route. I have a multimeter and if i knew what the specs were supposed to be on this Jeep, and the right order and procedure for testing it, i would. I have removal procedures for various sensors and install is reverse of removal. Alot of help there. Thx again 98jeepsrt6. BB in PHX

 

You seem to be going in the right direction fixing the known problems you have and solving the other as you go. How hard was it to replace that peice of the harness?? INspect the connectors too, may have burnt something there.. As for the CEL it might be working, you may not have any trouble codes. Not all related engine problem will toss a CEL. if you want to see if it throws a CEL disco one of the evap signal connectors, or as i do disco the upstream o2.. not take it out just unplug it.

But yea keep us updated and we will do the best we can to help you out.. Im suprised no one else chimed in though..

 

I see why you asked about the wiring harness. It is rough. Anyways am going to(hopefully) finish the wiring tonight and move on to the ign switch. Picked up a used PCM for $50!! Do you think i should hook it up and try it after the wiring harness or wait until i replace the ign. switch too? The CEL failure i was talking about is that it doesnt come on at all. Usually it will illuminate when the key is turned to the run position, just prior to cranking or turning it over, then go out. It stopped doing that entirely. I would hate to mess up this PCM. Im officially broke now. lol I dont know of any precautions i can take or testing i can do to be sure all is well other than double check my wiring work and go for it!! Any suggestions? Oh and thx once again 98jeepsrt6. Tangled up in wire here, BB

 

Good price on the PCM.. I want to say wait until you get the ignition switch in... ( do you have it off yet?) But you should be able to turn it ON (engine off) and test the other components that werent workin.. fuel pump, maybe your CEL will pop on, test spark at the coil. Im assuming you have a meter correct? The best thing you can do is once the PCM is in turn the car to ACC and test again before attempting to start. test the CEL light again for current.

 

Well i finally got the partial wiring harness installed, what a pain that was.... i had a few melted wires, i replaced the ignition switch also due to the burnt contacts, actually picked up another used one and replaced parts that were bad, another lesson learned. If you are thinking about trying to repair an ign switch for a 1995 Cherokee and it requires a tear down, BUY A NEW ONE!! It is worth the 35 $ Then before i installed the PCM, i double checked grounds and connections, put the under dash and steering column back together. Popped in the PCM, and fired it up!! Runs terrible, lol. But it runs. Its got a dead number 1 cylinder. same one that was acting up from head gasket. also had a bad wire into the CPS, brand new one too, but was able to work with it. Pulled the plug wire off of number 1 and it made no diff. while running. Worked my butt off for two days so i will pull the spark plug tomorrow and it will tell me everything. That along with the overheating makes me lean toward a crack in the head. I just wanted to let you know how it came out 98jeepsrt6. Your help was appreciated. I took your advice and saved some money. I was pretty much at a stand still not knowing what to do next. Thank you. I will let you know the final results. Im goin to get some sleep. Thx again bro. BB

 

I know this is a older thread but lookin for some advice I have the same prob as u did I have no fuel or fire but pump works when straight wired . How did u see a burnt spot on ur board with all the gell around it

 

Process of elimination limited my choices to the ECU, or PCM, whichever you want to call it, But knowing it was the problem, I simply flaked off the gel around the outer edge of the board, taking off as little as possible in case i could reuse it. I tried to repair it with some wire and solder, but no luck.If U have a friendly Jeep salvage yard in ur area, they may allow you to test out one of their known good ecu's to make sure. I also had some burnt wiring in my ignition switch, therefore not making the clean contacts,.I picked up an ECU for $50. So worth it compared to the time i invested troubleshooting it. Plug and Play, and drive. Good luck hope this helped. Barnyard Bill

 

Ok man thanks alot