scooter_350

Im new to the forum. I have looked at these numerous times when I come across issues that I have trouble figuring out, just never joined.

but I am having an issue with my wifes jeep. I have a 1999 jeep Cherokee 4.0l, automatic transmission, 2wd, with factory right hand drive. we have had this jeep for at least 5 years now. my current issue is that the I keep blowing the pcm fuse, in the fuse block under the hood. I believe it is the pm fuse. I have tried to search for a layout of all the fuses, but haven't found a definite one that I have. it is a 20 amp fuse. what I have done so far:
replaced alternator- it stopped charging.
replaced all the main power and ground wires- thought this could have been affecting charging issue.
ended up replacing the pcm- voltage regulator went out. was charging at 16 v.
after replacing pcm started blowing the pcm fuse after running for a while.
took engine harness out of jeep and repaired all broken and chaffed wires. (there were a ton.)
cleaned and made sure grounds in engine bay were clean and grounded.
checked crank sensor to made sure it was shorted in the sensor. there was no continuity between any of the pins.

after installing everything, the jeep fired up and sounded stronger than ever. I let it run for approximately 30-45 minutes to see it had fixed the issue. that is about how long( before the wiring harness repair) it would take when it would pop the fuse and shut down. I checked for a short to ground at the fuse and it was grounded. I started unplugging connectors to pin point it. I finally to the pcm and unplugged the gray plug. it broke the connection. I checked and found that pin 12 on the gray connector goes to the fuse that keeps blowing when I checked the connector to see if any wires were shorted to ground I didn't find any, besides what I believe to be grounds. the problem is I cant seem to find wiring diagrams to know for sure. but when I checked the pcm I found that pin 12 and pin 26 have continuity between them. this is all when everything was hot. I checked it this morning after everything cooled and plugged everything back in there was no continuity between the fuse that blew and ground. also there was no continuity between 12 and 26 on the the pcm ( where the gray connector goes.). I also noticed this morning that a 15 amp fuse still had continuity between it and ground. I believe it is for the o2 sensor heater. any help would be very much appreciated. I apologize the post is so long, but I wanted all the info I have done to be included.

thanks in advance for any help.

PatHenry

It sounds like you've done a dang thorough job in dealing with the electrical on the Jeep. Just out of curiosity, how hard was it to clean up the broken/chaffed wires on the engine harness? - it's something I'm considering in the future myself.

The FSM for your year will have all the wiring diagrams.

Fortunately, Cruiser has you covered - http://cruiser54.com/?page_id=365

From that page -- http://malcolm.iri5.net/FSM/1999_XJ_FSM.zip

scooter_350

it took about 8 hours once I got the harness out. it was a matter just taking my time and making sure I looked at every wire. if I found bare spots and the wire wasn't broken I cut the wire and put heat shrink on the bad spots. I soldered the wires back together where I cut them and then put heat shrink over them. once I got a section of the harness fixed I wrapped it with electrical tape to hold it together so I would know what I fixed so far. once I was completely done I wrapped the entire harness in electrical tape and put the plastic conduit on the wires I could and the part that was known for chaffing I wrapped in a rubber type tape that I had for added protection. when I put it back in I tried the best I could to reroute the part that goes behind the valve cover so it would help prevent future damage.

scooter_350

so I decided to try some more testing. today I put a new fuse in. the jeep ran for approximately two hours and didn't shut off. I was trying to figure what I did different. when I tried it before I had the lights on and the heater on. I turned the lights on and timed it. it was still running after after 45 minutes. I turned the heater on. I shut off approximately 15-20 minutes after I cut the heat. I was able to get my hands on a hard copy of the engine wiring diagrams. im old school. I would rather have paper in front to look at. but I looked at the diagrams and realized that the ac selector switch goes into the pcm on plug c pin 23. I have to try to get the wiring diagram for the heater and ac controls. to see where that wire leads me. the fuse that keeps blowing is fuse 21 in the power distribution block.

Turbo X_J

https://www.cherokeeforum.com/f2/f21...-again-196326/

scooter_350

thank you the response. I didn't see anything where they had a fix for it. but the wires that were referenced for the known chaffing, I have taken that harness apart and repaired any chaffing that was there. I think im gonna pull the dash apart and see if I can see any bare wires or chaffing in there, and hopefully find the root to my problem. I have been working on this jeep for the last month, it seems like I have been chasing my tail. but I know I have been fixing legit issues. it just seems like it never ending.

PatHenry

Scooter - I meant to ask you what sections of the main engine wiring were the worst spots?

I've got a set of battery cables from XJwonders that I'll be doing at some point after Xmas and I want to go through and check/fix any questionable wiring while I'm at it, but I definitely won't have a good 8 hours to do it. If I have a list of the most likely spots that need attention it would be super helpful so I can prioritize with whatever time I have.