Daily driven for a year then DOA! Dreaded crank no start. Please help

[TACTICALNAYNAY]

I’ve got a 1997 XJ 4.0 with an AW4 transmission and a 231J transfer case that's giving me a ton of trouble. It started with a rough idle—kind of felt like it was only running on three cylinders. My gas mileage plummeted to about 6-8 MPG, and acceleration was super sluggish, like I was riding a turtle or something. Plus, I'd get these weird hesitations when taking off from stoplights. So, I swung by O'Reilly Auto Parts to scan for codes since I don't have a check engine light (I think it’s burnt out or just gone). The scan pointed to a bad battery temperature sensor, so I replaced that.

After disconnecting the battery to reset the PCM and clear some codes, I hooked everything back up, and at first, it started and seemed fine. But then I noticed the alternator was dead. When I crawled under the hood, it started misfiring again, and the alternator still wasn’t charging.

I spent days digging through forums, and most folks thought it could be the PCM. So, I grabbed a new one and plugged it in, after making sure to disconnect the battery and wait an hour. But then, bam! No spark, no communication from the PCM to any modules, and I couldn’t get an injector pulse on either PCM. It was like someone flipped a kill switch; it would crank, but just wouldn’t start.

I have this list of tests from a shop that checked my Jeep, but they didn’t offer anything new. They wanted about $400-$500 to rebuild my engine harness because the injector plugs had some exposed wiring. Since then, I've replaced the battery, done a bunch of OHM and voltage tests, checked the wiring, and cleaned up all the grounds and connections.

I need to get my daily driver back on the road—my shop truck just isn’t cutting it! If you need any more info, just let me know. Thanks a ton!

 

[Anak]

Post up the list of tests and the results of those tests.

 

[TACTICALNAYNAY]

Things that I have tested with incandescent test light or a voltmeter I will get the results from those tests when I get home from work;

Crankps
Cps
Coil
Spark
Voltage on injectors
Asd relay slot 87 and 30 in the PDC
all of the fuses in the PDC and Junction box

I have 5v going to all of the required sensors for start up, when I put a test light on the coil 12v supply and turn it over I loose the light, my ASD relay clicks, after that the light comes back on. When I turn the jeep over by hand I can hear all of my injectors click so I know that it is getting signal from the flywheel

 

[lawsoncl]

So it won't start at all after swapping the PCM? That could be anti-theft or the PCM isn't the right one. I'd swap the original back in and continue troubleshooting.

In your PM you said - "I have a list of things a shop did to test and diagnose the Jeep, which I can send you if needed, but unfortunately, they couldn’t provide any additional insights. They did suggest spending an extra $400-$500 to have them rebuild my engine harness because my injector plugs show some exposed wire near the pin connection."

Try wiggling and moving the harness across the fuel rail and where it crosses over to the firewall. If that makes it stumble or get better, then it's likely the wires are frayed or damaged in the wiring harness. This is usually caused by bad motor mounts, btw. You can also pull off the injector connections one-by-one while running to see if any don't affect the idle. I'd also unplug the O2 sensor and see if that helps, to rule out a bad O2 sensor.

 

[TACTICALNAYNAY]

The new pcm is compatible with my original computer and the new computer did not have the SKIM system as far as I am aware, but no it will not start with either computer I will try to wiggle the wires and see if it uncovers something more. Also I have tried to put the old pcm back in after I had the harnesses out and it was the same thing a crank no start/no spark I've been over this jeeps engine bay top to bottom left to right…. Its been down since October

 

[Anak]

In one place you say "couldn’t get an injector pulse on either PCM", in another you say "I can hear all of my injectors click so I know that it is getting signal from the flywheel"

I am confused.

Have you plugged in a noid light?

Among missing details, what is your fuel pressure? (As in a definite number, not "I pushed the Schrader valve and fuel came out".)

How has the coil been tested?

 

[TACTICALNAYNAY]

In one place you say "couldn’t get an injector pulse on either PCM", in another you say "I can hear all of my injectors click so I know that it is getting signal from the flywheel"

I am confused.

Have you plugged in a noid light?

Among missing details, what is your fuel pressure? (As in a definite number, not "I pushed the Schrader valve and fuel came out".)

How has the coil been tested?

No I don't have a noid light but I do have a test light. 49psi fuel pressure when key is on the fuel pump comes on for 2-3 seconds then shuts off. I started to hear the injectors click after I repaired the injector harness I can physically feel them click. The ignition coil was tested for ohms as well as I have used my test light backprobing while cranking, the coil tested a little out of spec the primary coil was at 1.5k Ohms and the secondarys were at 9.30k Ohms. I currently am making sure that the TPS, Crank position sensor and the map are getting 5v reference which they are.

 

[Anak]

Have you checked for a grounded out O2 sensor? Those make for an unintended kill switch.