thisismyusername

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Hello all. I wanted to gauge opinions.

I had some issues a year ago where the jeep just wouldn't crank (turn key, nothing happened). I thought it was the starter, which I replaced but it continued happening. Then within the last few weeks my jeep started stalling randomly. It only happens after it's been running for a while. Once it stalls it exhibits the same no crank issue. With the key in the ignition, the odometer displays "no bus" and none of my gauges will move. My ODBII reader can't communicate with the PCM. If I let it sit for a while and cool off, it will start back up and the gauges are happy.

I posted this a couple of weeks ago. I thought potentially it was based on the CPS. I replaced it but the problem is still there. On Saturday I touched the PCM when it stalled; it was very hot. I unplugged the PCM and I get the exact same symptoms (no crank, no click, no bus error, no gauge readings). I let the computer cool down, and it cranks right back up like nothing is wrong.

I'm thinking the problem is the PCM. I believe there is a component on the board which is failing when the board gets hot, and the problem is getting worse the more I use it. In desperation, I ripped open the PCM to inspect the electronics. I expected to see a damaged component but I couldn't find anything. All the electrolytic caps look fine.

At any rate, the PCM is in no state to put back into the jeep. (I did plug it in as a test after I opened it and it cranked right up). I'm going to buy a refurbished one (flashed with my VIN) and cross my fingers.

The only other thing I can think of is if there's a short in the harnessing which is causing some component on the PCM to get hot and take down the PCM until everything cools down. I have inspected all my harnessing and wiring and it all looks fine. Anyone have any other advice?

Model: 1999 TJ 4.0L
Mileage: 145,000
 
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@thisismyusername
Hello all. I wanted to gauge opinions.

I had some issues a year ago where the jeep just wouldn't crank (turn key, nothing happened). I thought it was the starter, which I replaced but it continued happening. Then within the last few weeks my jeep started stalling randomly. It only happens after it's been running for a while. Once it stalls it exhibits the same no crank issue. With the key in the ignition, the odometer displays "no bus" and none of my gauges will move. My ODBII reader can't communicate with the PCM. If I let it sit for a while and cool off, it will start back up and the gauges are happy.

I posted this a couple of weeks ago. I thought potentially it was based on the CPS. I replaced it but the problem is still there. On Saturday I touched the PCM when it stalled; it was very hot. I unplugged the PCM and I get the exact same symptoms (no crank, no click, no bus error, no gauge readings). I let the computer cool down, and it cranks right back up like nothing is wrong.

I'm thinking the problem is the PCM. I believe there is a component on the board which is failing when the board gets hot, and the problem is getting worse the more I use it. In desperation, I ripped open the PCM to inspect the electronics. I expected to see a damaged component but I couldn't find anything. All the electrolytic caps look fine.

At any rate, the PCM is in no state to put back into the jeep. (I did plug it in as a test after I opened it and it cranked right up). I'm going to buy a refurbished one (flashed with my VIN) and cross my fingers.

The only other thing I can think of is if there's a short in the harnessing which is causing some component on the PCM to get hot and take down the PCM until everything cools down. I have inspected all my harnessing and wiring and it all looks fine. Anyone have any other advice?

Model: 1999 TJ 4.0L
Mileage: 145,000

Hi! Did you ever get to the bottom of this? I have a similar issue, but would not want to get a new PCM and migrate the same issue to the new one.