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96 XJ - engine died on highway, cranks, doesn't turn over.

fsupaintball

NAXJA Forum User
96 XJ

I was on the highway at normal operating temp, hit the button to turn off cruise control (coincidence maybe), and my engine died. Electronics all stayed on. Pulled over and tried to start up. The starter cranks good and hard, but the engine never turns over.

I messed with my shifter (neutral safety switch), re-plugged the CPS harness, tried swapping the fuel pump relay, no difference made. Towed to a Big O near work to see what they saw.

Errors pulled: P1389, P1388.
"Auto Shutdown Relay shut and open; no auto shutdown relay voltage output at PCM"

They also say 12V should be coming from the PCM, and they're only seeing .3 volts. They tried swapping in another Crank Position Sensor and it made no difference.


Anyway, they sounded a little unsure but said the next step is a $500 PCM replacement. I'm trying to figure out what to do next. Suggestions?


Other notes:
-I'm fighting an overheating problem with this Jeep, but it was running at a normal temp at the time.
-About 2 weeks ago I swapped BOTH manifolds, and put in a 97+ style intake manifold and swapped around some vaccum hoses to make it all fit. The hoses look OK.
-Neutral safety switch was replaced a few months ago.
 
If it cranks, the NSS is not a problem.

DELETED.

Don't have the 96 manual. Through 95 the PCM controlled the GROUND for the ASD relay, not sure for 96+.

They aren't out of line on price, installed, if they are charging you full list price for a reman PCM. However, I would try a recycler or car-parts.com (searchable recycled parts throughout U.S. and Canada) car-parts.com shows plenty available $125 and up.
 
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I'm having it towed to another shop. I think I'll get a couple relays tonight and try swapping them around, as well as check the CPS pins for resistance myself tonight while in the parking lot.

I'll see if I can figure out how to check the PCM pins like you mentioned.
 
I'm having it towed to another shop. I think I'll get a couple relays tonight and try swapping them around, as well as check the CPS pins for resistance myself tonight while in the parking lot.

I'll see if I can figure out how to check the PCM pins like you mentioned.

Just unhook the connectors from the PCM under the hood. It should be in the 60-pin connector, but not sure as I don't have the 96 manual.
 
Hopefully they have:
Checked all fuses in the PDC
Checked all fuses in the Junction Block
Checked all grounds

turning the key to the start position should activate the ASD for about 3 seconds, which should pass 12 volts thru to the PCM so you can see the voltage there for about 3 seconds and then it will go away when the relay opens again without a crank signal. When you turn the key to the run position and crank the engine, the PCM should detect the Crank Position Sensor signal, and keep the ASD relay grounded and energized and the 12 volts should stay.
 
FIXED! Bald O2 sensor wire against the exhaust manifold caused this.

It was my own damn fault. A couple weeks ago I swapped in a 97+ style intake manifold. Neither myself nor my buddy noticed that the front O2 sensor wire was laying up against the exhaust manifold after we got done.

In troubleshooting tonight, we first swapped an identical XJ's PCM with no improvement. We then noticed that the 30 amp mini-fuse was blown, and would blow immediately each time I tried to crank the engine. Research showed that the fuse supplies to the coil, alternator, PCM, and O2 sensors. I was about to start unplugging them one at a time to figure out which was blowing the fuses, when I found the wiring issue.

It had melted through the casing on one of the wires, grounding it against the exhaust. Some electrical tape and rerouting the wire was all that was needed. It cranked right up after that.

Thanks for the advice guys. And to Big O, all I can say is SUCK IT. I suck at this, and I was able to figure this out. You guys looked at this for hours...
 
Thanks for the advice guys. And to Big O, all I can say is SUCK IT. I suck at this, and I was able to figure this out. You guys looked at this for hours...

Tire guys--what can you say.
 
Glad you got it fixed! It is amazing how may problems will either get fixed, or put you on the right troubleshooting path if you:
Checked all fuses in the PDC
Checked all fuses in the Junction Block
Checked all grounds

have a great weekend!
 
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