1996 XJ sport AT
Just bought it as a project someone else started. It will start and runs perfectly. But only with I get the "GEN" & "Check Engine" MIL to stay lit. Only way to get it to stay lit is turning the ign a bunch of times. Some of the time it just flashes. But here is the twist.
1. The wires going to the brake pressure switch where burned. Both wires all the way to the firewall. Then the other side of the firewall to the ign switch. I have opened the wire harness pulled all the wires apart. Where the wires touched or crossed other wires it had melted them together. All of that has been pulled a part and wires checked for continuity. I think I am good there. Before I did that. The door buzzer would just buzz even with no key in the ign. That has stopped.
2. I really don't know what the "brake pressure switch" does. I am not talking about the brake light or parking brake switch. This is the one on top of what looks like a proportioning valve. Will that cause a problem with the PCM? Right now I have all the wires cut out. They were completely melted.
3. I know the PCM has checks it has to do like a "POST" (power on self test). If the brake pressure switch is not connected will it cause that to fail?
4. Also when the "GEN" & "Check Engine" flashes or does not come on. I cant get a connection to the PCM via OBDII and the fuel pump just runs. When it works correctly. They lights come on for a few sec and fad out like they should and the fuel pump stops and I have a OBDII connection with no fault codes.
5. Also I have not been able to get any fault codes when it does start.
6. Every now and then. I will get chatter of the ASD relay and the Idle Speed Motor. I have replaced the ASD relay. I have swapped it with a known working one. No change.
7. I have tested the wires from the ASD to the PCM. They are good.
8. I have already checked my 5v references. They appear to be fine.
9. I have done a ton of search's. The wires to the O2 sensor keeps coming up as melted. I have checked that.

Currently I have the dash out. I have the whole wire harness unplugged with the only the connections to the MIL, Fuel pump and the ign switch connected. With the exception of the one wire at the ign that goes back to the brake pressure switch. Yet nothing has changed.
I have caught the MIL lights on video. Both working and not working. I can post if needed. I also have pictures of the burnt wires to the brake valve if anyone wants to see them. I have a subscription to AllData. But it is pretty hard to find what I need.

Next steps... I was going to start checking pwr and grounds at the PCM.

Just found this too... This sounds just like my problem. With the exception of the brake switch problem. But there is no resolution.
https://www.scannerdanner.com/forum/....html?start=17

I can't be the only one that was had this problem? Any help would be greatly appreciated.
If anyone has a good 1996 wire harness I would love to talk to you. Both the eng and the dash side. But the dash side is in the worst shape.

 

I'd triple check that none of the wires are shorted to hot/ground/each other, but if you're sure they're not, it sounds like the ECM has issues and needs replaced. The Fuel Pump continuing to run suggest the same.

The switch on the proportioning valve illuminates the same Brake light as the Parking Brake does when there's a leak in either brake circuit.

I agree with verifying good power and ground to the ECM. It should be operating the same every time. If it doesn't, it more than likely has issues and needs replaced.

Follow-up question, maybe someone knows. Other than the OBD connector, how much different is a 91-94 Dash harness from a 95-96? Might be easier for this gent to rework a 91-94 harness if he can't find a 95-96. The engine harness can be adapted by changing out the plugs to the ECM.

 

I am leaning towards a PCM too. But I also don't want to be that guy that just replaces stuff..lol

One think I have been able to do and repeat. If I turn the ign to run pull the ASD relay. Then put +12 on the hot wire that crosses the relay for a sec. Then turn the ign to off replace the relay. It wants to work.
I know that does not make sense. There is no reason that should work. But it's the only thing I can repeat and it works and starts and runs fine.

I just had no idea before I bought it 1996 was all one year only this and that.

 

If I do need to buy a PCM. If anyone has a someone they would recommend that would be great.

 

I'm in a similar situation with my daughter's '96 XJ, finding that there are 2 major configurations on this platform has been a challenge.

Currently in a spot where it acted odd for a week (right after a SoCal cold snap, broke below 30degrees at night) with struggle starting, needing to hold idle with the throttle until it warmed up, and finally it died coming to stop at a light. Now it doesn't start at all and while I get voltage at the coil output while cranking, I'm getting zero voltage through the dist-cap.

I've replaced the Crank Sensor, even replaced the cap/rotor/pickup coil/cam sensor. Still same crank but no start. Its a new battery, the ASD relay I can hear operate (plus I see the voltage at the coil when moving key to RUN). I'm starting to lean towards the ECM/ECU and have a local company here in Riverside that tests and reprograms them that I'm going to try.

 

forgot to ask... I assumed you were an ODB2 setup?

 

[QUOTE=netdawg;3694506]forgot to ask... I assumed you were an ODB2 setup?[/QUOTE

Yes OBD2.

 

So the ASD relay in mine was fine. I even took one and cut it open so I could watch it. I did a bunch of reading. The PCM has to send a ground to make it work. I don't remember all the details. But it is tricky how it works. I was able to turn the IGN on pull the relay put pwr to a pin. Then put the relay back and it would start.

What I ended up doing.... I bought a dash wire harness on Ebay out of a 96. Pulled the relays and fuses for pwr lock..etc. The stuff I did not have. Still did the same thing. But now I don't have the melted wires. Then I felt comfortable getting a PCM. I did not want to just pop a new PCM. After a ton of homework and lots reading. I went with wranglerfix dot com. I know I paid more than other places. But the owner will talk to you is active on forums. I figured with the strange problems I was having support and help was worth it. They shipped right away and it fixed it. This is a project XJ so I have not driven it more than around the block. But it starts every time now.

Since I had the dash out I am rebuilding the AC/Heat box. As soon as that is done I will have a better idea how well it really works. But it did fix the problem.