Son's 98 XJ is giving me fits.
Rough idle, Wont start (intermittently), Stalls. Stalls while driving.
Did my research here and cleaned the TB and replaced the IAC (couldn't find a mopar part on Sunday so opted for the BWD from O'rielly's) yesterday. XJ fired up and idled smooth in driveway for a long time. A good 30 minutes or longer. Spent the rest of the day replacing the seats and other stuff that was missing from the interior with beautiful parts I found at the Pick A Part. I'll post some pics later today. Drove the XJ to pick up some Pizza's. All was good in the world.
My boy got up for school this morning and didn't make it out of the neighborhood. By the time I got to the jeep the battery was dead. I ran home and grabbed the battery from my WS6 and put it in. No start unless Im mashing the pedal, wont idle, dies immediately when I get off the gas.
For ****s and giggles I left the key in the on position (priming the fuel pump) and poked the fuel rail. No significant pressure. Initial fuel spurt, then a trickle.
The fuel pump should be pressurizing the entire time the key is on right?
I had read the CPS if bad could cut power to the pump. Is this right?
A little guidance please. Need to get her running so my kids have a way to school.

 

I would suspect fuel pressure being an issue. Try the "poor man's prime"-- turn the key until you hear the pump, shut it off, turn the key to run again and hear the pump, and do that 3 times, and then try to start. Does it start then? If so, you have a fuel pump problem. The best way to confirm is to rent a pressure tester from AutoZone or similar and verify fuel pressure. I believe it should be around 49PSI.

 

I never really hear the fuel pump pressurize. Ill go get a tester as you suggest and try that. The pump should keep constant pressure while the key is in the on position correct?

 

Correct. Also, after you do the "poor man's prime", put the tester on it with the switch totally off. If you see the fuel pressure dropping, it means that the fuel is leaking back into the gas tank, which is an indication of a bad check valve on the fuel pump module. On the 98's, your best bet is to replace the whole module as one. I got one for about $150 bucks on Amazon. Bosch or Carter only.

 

When the key is turned to ON intially the pump should only run for about 1 to 2 seconds then turn off.

If you don't hear the pump run at all check the fuel pump fuse in the PDC (pic). If the fuse is okay, swap the fuel pump relay with the electric radiator fan relay and try it again. Relays are identified on the inside of the PDC cover. If the pump runs now, replace the bad relay.

If the fuse is blown, try another fuse. If it blows again, unplug the fuel pump connector at the gas tank and try a new fuse. If it doesn't blow there's a problem inside the pump. If it does blow the new fuse, there's a short between the fuel pump relay and the connector.

 

Picked up the pressure tester.
Knelt down near the rear wheels while my Son primes the pump. I hear it engaging.
Tester gauge reads 46-48 lbs. after 3rd prime.
The XJ starts and holds 46-48 lbs.
The XJ does stall once and requires re priming to start again.
With the key in either the off or on position the pressure bleeds down.
Correct me if I'm wrong, but a fuse or relay would be either good or bad, not intermittent.
It also appears to me that the "prime" only pressurizes the rails in order to start the XJ, as the pump shuts off after the initial prime.
Where does the pump get its signal from to engage when more fuel is required past that point? The CPS?

 

yes.

 

Ok, so what did I learn? Based on information posted above.
Check valve in the fuel pump module not letting the system hold pressure.
Fuel pump not supplying enough fuel. 46-48 psi


Diagnosis?
Complete fuel pump assembly.
Figures, I just topped off the tank.


Should the fuel rails pressurize to 49 psi on the initial single prime?

 

Gremlins Update


based on the above troubleshooting, I bought a complete fuel pump module (carter)from rockauto.
I installed it last night. Son needs a car to drive to school.
Had the battery out during this time on a charger because my Son ran it almost dead trying to start the XJ from an earlier posting.
I listened for the prime and heard it do it's thing.
The XJ fired right up and idled. While I was busy patting myself on the back, She stumbled and stalled.
I thought " no big deal, the computer just needs to get it's **** together".
Re primed the pump and she fired up again. Pushed the release on the fuel rail, more pressure than with old pump, based on fuel spurt. Stalls again. And so on.... Holds an idle for 10 minutes or so, so I take it for a spin in the neighborhood. No issues, seems more responsive actually.
Son takes it for a spin too, he has no confidence in his XJ now and is afraid to break down on the road but she seems fine and home he comes with a smile on his face.
I get up and go to work this morning at 4:45am thinking all is well in the world until I get a text at 7:00 that the XJ won't start again. Just got home tonight and went out and listened for the prime. Turned her over, did not even attempt to fire up. Just turns over and over.
Somebody shoot me please. I normally work from Dark to Dark which doesn't leave me much time for these driveway repairs.
I think the next course of action should be to re rent the fuel pressure tester just to see how it differs, if any from the module I removed. Then I'm out of ideas. Somebody please point me in a direction.

 

So when it turns over and over, did you hear the fuel pump prime then? I'm thinking a possibly electrical issue with the pump or maybe the relay.

 

One or more dead cells in the battery?

 

tell me more....
He's run the battery dead at least half a dozen times in the last 6 months. Lights on or dumb **** like running the A/C without starting the car.

 

You can't really run the A/C with the engine off. You're probably talking about the blower motor. But anywho, does the starter run real sluggish? Might want to test your battery...couldn't hurt

 

49 PSI is fine...spec is 49 +/- 5 PSI