91 4.0L Died, cranks, no start

[Phil]

Ok, so I was coming back from regearing my D30 and stopped for a burger. I was headed back towards my place and stopped for a stoplight, turning left. I had the radio on, so I didn't hear if there were any unusual sounds. No tachometer, so I didn't see my RPMs die.
Anyway, it did die in the middle of the intersection. I put it in N and was able to get it started again, but I don't even know if I was able to shift to D before it died again. It would not restart after that first time. Didn't think to turn off the radio and see if I could hear anything, I wanted out of that inersection.

Now, it will crank but it will not start. There is fuel to the rail. When I turn the ignition to the run position, I can push in the pressure release and a little gas will spray out. Only once though, is this right? Pressure will not build back up.

What do I do now? I really really do not want to just throw parts at it.
Thanks for your help!

[Danno]

My Ford diesel did the same thing on me tonight. Only 66k miles on it also. Quit down in Alabama about 50 miles from home. Oh well... we were in kansas yesterday at this time. Check to see if it's fuel. Take the hose off at the throttle body and have somebody briefly crank it. If not then its electrical.
You'd think it's a full moon out tonight. Wait, it IS a full moon!!

[NotMatt]

Crank Position Sensor maybe? I know they're pretty prone to just giving up the ghost at the worst times, and would cause it to crank but not start. I haven't ever had a problem with mine, but I have a spare in my center console for when disaster strikes.

[Eagle]

Turn the key to the 'Run" position (not "Start") and listen for the fuel pump. If you don't hear it run for several seconds, check the fuel pump relay. Also, I don't see an indication of the year, but if you have a fuel pump ballast resistor also check that.

[Phil]

This is a 1991 Jeep, but the engine was replaced in 1999, coming up on about 50,000 miles ago. I think it would have been replaced with a rebuilt 91 or something close. Would a 1991 have the fuel pump ballast resistor? Searching tells me it would be by the air box if I have it, and the pump relay is in the fuse box behind the battery, correct? And how do I check them?
Thanks!

[Walt Stanley]

The CPS test, that sometimes works, is to disconnect the CPS at the point near the rear of the valve cover on the drivers side. Disconnect and reconnect and see if it starts. If it does start the CPS is on its way out and needs replacement. If it does not start, it still may be the CPS.

[Phil]

Ok, I'm going to go check on it, but BTT for this!

[4xBob]

As above, I'm betting CPS. Nobody mentioned yet that a failed CPS results in no spark- so, check your fuel pressure and check for spark. 4xBob

[Phil]

Ok, I disco'ed and reconnected the CPS, no start still. Went down to Kragen to see if I could get a CPS anyway, they only showed them for a 4.0L Auto Wrangler, and a 4.0L MT Comanche.
Does MT vs AT matter as long as I get one for a 4.0L Comanche?
What else can I check?

[yellowxj]

see if you can "rent" a fuel pressure gauge from the local parts store, thats a easy cheap test....or my xj's personal favorite bad computer ....after you put a new cps sensor in if it still doesnt run and you dont have spark then it may be the computer...to see if you have spark get a "good" friend to hold a spark plug wire while you crank it...if he jumps you have spark

[Bryan C.]

Originally Posted by Phil Weeks

Ok, I disco'ed and reconnected the CPS, no start still. Went down to Kragen to see if I could get a CPS anyway, they only showed them for a 4.0L Auto Wrangler, and a 4.0L MT Comanche.
Does MT vs AT matter as long as I get one for a 4.0L Comanche?
What else can I check?

I would say to see if they have a CPS for a 91 XJ 4.0l auto. The MJ and XJ use the same parts. Not sure about the MT vs. AT. Ok so you say you get a shot of fuel pressure when you turn the key on, but not when cranking? This tells me the computer isn't seeing a RPM signal and not actuating the fuel pump. Some posted about checking for spark, good idea. If you get no spark while cranking, and the fuel pump isn't running while cranking, change the CPS. This part goes out often enough and is cheap enough to just throw it in and see what happens.

Good luck, it really sucks breaking down.

Bryan

[Hack]

Hey Phil-

I am having the same problem, worked fine for the drive home and then would not start the next day. Cranks but that is all. If you figure it out lemme know and I will do the same...

[Phil]

I called Kragen and for an XJ 4.0L auto it was about $125 and for an MJ 4.0L MT it was only about $50. Does that sound about right? So I'm hoping to hear from the dealership that auto/MT doesn't matter so I can get the cheaper one. Planning on calling around too. Is $50 cheap? Well, I guess maybe for Jeep parts. [Edit]I went over there and checked it. It has pressure but if I release the pressure and then try to crank, pressure does not return.[/Edit]

Hack, at least you got home! I was in the middle of 2nd and Mace! I don't think I'll have enough fun replacing mine, if it works we can do yours.

[Hack]

That can be a bad intersection during the afternoon, not the first place I'd want to have a breakdown.

I need to set aside some time this week to get in there and find out what is causing the problem.

[Phil]

I just got off the phone with the dealership and they wanted $126 for a CPS for my truck. Is that about right? Kragen wanted $125! That is not a cheap part!