why do you say the pcm?

According to Haynes there isnt one in the 99 and down Cherokees, only in the 2000-01, when they switched to coil packs. but what the hell do I know...

 

hope not , my 2001 crank not start gauges not moving fuel bump works every thing works but no start changed the CPS try every thing it was bad PCM they go bad suddenly without check engine light , i may be wrong and i really hope im wrong, but check your PCM

 

Did gas do any thing ?

 

You have not completed my checklist of things I outlined in post #13.

These are really important steps. Trust me; I've worked on countless no starts.

The PCM is the computer. All 4.0 engines have one. They have been called ECM, PCM, etc. But they are all the computer.

 

Hey, I just posted a long reply and the computer pooped its pants so here is the slightly shorter, kind of annoyed, version.

I havent been able to respond for most of the day because for some reason I cant type replys on the tablet. I checked all the fuses and can confirm that the fuel pump does not cut on when the key is in the on position (this was actually the first thing I noticed when I tried to start the jeep a few days ago as I always prime the pump a couple times and listen for that sound before starting).

My gf worked a double today and doesnt get out for another hour but then she is going to help me check for spark. I didnt want to do the starting fluid in the tb until after I did that (as per tjwalker's instructions). I am planning on doing both of those things as soon as she gets here.

Kind of a rough day basically. I think I mentioned this before, but I am very new to this area and dont have the support network of friends and family like I do back home so it is difficult even getting a ride to and from autozone. Throw in a 15 month old baby and a tight budget and you've got one heck of a headache.

Cant say enough how much I appreciate all the help Ive gotten so far, and I assure you I am working on accomplishing the things you all have suggested.

When I checked the fuses all the blade fuses are fine but the relays for the fuel pump, starter, and ads look like they are shot. Im not sure how to tell really, since they arent translucent like the blade fuses, but there is some burning on a few of the flanges (not sure if that is the right terminology), numbers 87 and 87a if I am not mistaken. Its the same two on all three relays. I did manage to get to autozone but they did not have them in stock, had to order them for tomorrow morning. At 16.99 a pop Im glad they didnt make me put the money down... I hoped you all could tell me if there is a way to definitively check their viability.

Spent allot of time reading my Haynes, familiarizing myself with the various systems that could be involved.

I will post back asap when I have more to report. Thanks again.

 

Just checked for spark and got nothing whatsoever. Unless I did it wrong...

Pull sleeve off of plug, hold 1/4" from good ground (I tried on the firewall and on the block, the only two places the wire would reach), had my gf crank it. Nothing.

 

Okay, no spark that tells you a LOT.

Although there certainly are a few possibilities, the #1 cause of no-spark is a bad crankshaft position sensor.

As long as you already have them ordered, definitely try a new ASD relay in the power distribution center. A faulty ASD relay can inhibit the fuel pump from kicking on and will also inhibit spark. The old relays really shouldn't have any burning or discoloration on the contacts; that is a possible problem that you may have to dig in further. But first, see if a new ASD relay and a new fuel pump relay makes a difference.

A faulty coil can result in no-spark, but if the coil is the ONLY problem, you should still hear the fuel pump energize. And if you are positive that the fuel pump is not energizing, the problem is not likely the coil.

I've outlined how spark works on the 4.0 below. A problem with the ASD circuit somewhere or a faulty crank sensor might be the culprit here.

Good luck and keep us updated!
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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.

 

I'm totally confused.
I'm 56 years old and have always used the following terms:

Turning over ..... when one engages the key forward and the engine, well, turns over.

Cranking ..... when the engine starts running.

My 27-year-old daughter and I just had this same confusion yesterday. Have I been wrong all these years?

I realize that its just semantics but....wholly hell....how does a set of terms become opposites?

 

CF, you are my hero(s). Fixed the Jeep last night, it was the cps. Fired right up when i changed oit the part.

Tjwalker, i cant really tell you how much i appreciate your help. You saved me allot of money i dont really have, not to mention time and my job. Thank you.

Freegrd, you got me on the right track and were also a huge help in figuring this out. Thanks man.

 

Hey GreyDog, glad we could help! Always nice to see a happy ending, even though getting there wasn't a straight line........troubleshooting often isn't.

Enjoy your XJ!