Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.

 

Thanks TJwalker. I had to stop working on my daughter's jeep for a while. Last week was hunting season.

The power shuts down quicker than I thought it would so I will need to have my daughter crank or at least turn on the power while I have the multi-meter on it.

I am wondering if no power is coming ot of the ASD relay when the ignition is turned to start position which would you suspect first, faulty PCM or CPS?

Thanks again.

 

I think I may have it fixed. After checking the volts going to the coil from the ASD relay I was only getting about 5 to 6 volts. It spiked up to 9 at one point, but only briefly. The battery had been dragging a lot as well with all the cranking, and I was noticing that it really didn't take a charge like it should so I replaced the battery. The battery needed replacing as the tag on it indicated it was about six years old. After replacing the battery it fired up and is running well.

I then cleaned up the connections to the starter and changed the oil since I was right there, it was due for a change.

I am wondering if I had the original problem fixed and the weak battery just exacerbated the symptoms. I guess I will find out to day with a test drive.

Thanks for all your help Tjwalker. You really helped me learn a lot about diagnosing problems and XJ ignition wiring.

 

I had a problem like this with my 95 Cherokee. It ran fine...........then I was heading down the interstate home after work one day a couple months ago. It lost power and quit running. I have 220,000 on the odo. I thought the fuel pump had took a dump. I sat on the side of the road for 20 or so mins talking to my wife about getting the Jeep towed. As a last ditch I tried to turn it over and she fired up!..... and I took off. Got almost home and it quit running........ this went on for the next several days while I trying to figure out the problem. Turns out the problem was crank sensor. It would run till that part got hot and then it would loose fire and quit running. That thing is located on the bell housing. A real pain in the rump to change. This kinda sounds like what happen to my jeep. Hope it may help.

 

Idrum6969 thanks for the help. The crank sensor is the first thing I replaced so unless the new one is bad I am thinking it may be with the PCM.

The reason I say this is because yesterday my daughter barely made it to school with the jeep. Once there it would not start. It would crank, but not fire. Tonight I checked the volts on the plug going to the coil while my wife turned it over. The volts read 9.3 fairly consistently. I then put my code reader (Equus 3030 as tjwalker suggested) on it and pulled code P0351 which refers to "Ignition Coil 1 Primary Circuit Malfunction" or "Ignition Coil "A" Primary/Secondary Circuit Malfunction" depending on which site you reference. Since I have already replaced the coil and leaning toward thinking I am dealing with a faulty PCM. I went to the local pick a part and they did not have a 96 XJ, just an 89, 91, and a 98. I am pretty sure none of those will work for me. I plan to check around some more tomorrow, but I suspect I will be forking out for a new one.

As always folks I am open to suggestions.

Thanks

 

Just curious, does anybody know if a PCM from a 96 Grand Cherokee with a 4.0L work in my daughter's 96 XJ? The local pick a part had a few GC's but I did not look at them.

 

Any update or resolution? I'm in the exact situation and haven't figured it out yet

 

Sorry if your question has been solved, but im at work and dont have enough time to read ur whole thread on my phone. As I have told so many people that are having this same type of issues with the Cherokee:
I had the same problem with my '92 and 94 Cherokees. If u have spark, gas, and air then u have ignition (in most cases), but if ur computer is shuting off ur gas or ignition every time u try to start, or intermittently while u drive (usualy when u hit a bump, or when the engin reaches running temperature) im 90% sure its a bad/dirty Crank Positioning Sensor. Crank sensor has a little wire rapped around a magnet. Every pass of the crank causes a megnetic charge to be conducted into the coiled wire which is sent to the computer (as best i can explain it in short). If the wire is shoring out, a little bump will cause the engine to missfire and die. If the megnet is week the magnetic field is weak and the computer wont send a signal to fire the plugs. If the sensor itself is dirty it will do the same.

My best suggestion since u live far from a auto parts store is to take off the sensor and clean it. If u want, drill the bolt holes ON THE SENSOR (not bell housing) one size bigger then when reinstalling, hold the sensor tword the bell housing causing the sensor to be closer to the crank which would correct a weak magnet (temporarily). If it fires back up then u realy need to get ur girl a new crank sensor (u dont want her getting stuck somewhere down the road.

Sorry for my bad spelling. Im using my phone for this. God bless

 

Sorry guys, I never thought to follow up on this.

Ultimately, it wound up being the pick upcoil in the distributor. Once I replaced the pickup coil it fired right up and has run well since then.

Hope this helps.