Jeep died on me this morning...

96 XJ 4.0 5 speed

At least it had the courtesy to do it in my parent's driveway. Started up and ran fine on the way over to drop my dog off, then as I'm standing outside talking to my dad for a couple minutes I can hear it sputter a few times as it's idling in the driveway. Then as I'm walking up to it, it just shuts off. Get in, crank a few times, sputters, then eventually fires up. Against my better judgement, I set off down the driveway, only to have it die again a few hundred feet up the street. Restarts again, and I decide not to press my luck, so I turn around, park it, and take their extra truck to work.

No real symptoms that I noticed until it started sputtering in the driveway, drove fine all weekend and on the way over to their place. It might have started a bit hard this morning, but that's not uncommon on cold days. The last time I drove it yesterday was to the car wash and I did give the undercarriage a pretty good soaking in the self serve wash bay. Doubt that caused anything, but thought it might be worth noting at least.

My gut feeling is it's a fuel issue. I'll pick up a gauge and test the pressure tonight. At least the tank is pretty low at the moment, in the event I need to drop it. Any thoughts from the hive?

Sounds like a fuel issue, but don't rule out crank position sensor. A common 4.0L issue

Isn't the crank position sensor an all-or-nothing kind of deal? As in, it runs perfectly or not at all?

Let the Jeep cool down and then see how it runs. If it runs fine once it cools down but gets flaky when hot (especially when idling and the engine bay starts to heat up), it's most likely a bad crank sensor.

Ahh, good call on the CPS, forgot that was a thing on these. Should definitely be good and cold by this evening, so we'll see if it fires up then. If so, try to limp it home and further diagnose.

fuel pump...

How about fuel line freeze-up

How much fuel in the tank? How new is the fuel filter?

I had a car with rusty bits in the tank, every once in a while some schmegma would get sucked up into the fuel line and stop fuel delivery, let off the gas the crap would fall back into the tank and it would be fine until next time.

Dropped the tank and flushed it out with Eastman's Metal Wash, a new filter and all is well.

Dan

jstein77 wrote: Isn't the crank position sensor an all-or-nothing kind of deal? As in, it runs perfectly or not at all?

Mine wasn't. It was intermittent as hell, making diagnosis a bear.

Rust bits are possible, a 96 does have a metal fuel tank.

For the CPS, they can definitely be intermittent. Last one that failed on me worked fine if the engine bay was kept cool, but would cause random misfires if it got too warm and if it got warm enough (like idling for more than a few minutes), the thing would just crap out and wouldn't run until it cooled for a bit.

It's got somewhere around 1/4 tank of gas and the fuel filter is ancient (been meaning to replace it but keep blowing it off.) So there's definitely reason to suspect it may be plugged with E36 M3.

As for the CPS, this morning's issue would have occurred right about the time it would be hitting full operating temp. I still tend towards it being a fuel issue though, didnt feel like a misfire, more like an "I'm being choked for fuel" sputter and die.

So my plan is:

1) Test fuel pressure.

2a.) If fuel pressure shows good, replace CPS.

2b.) If pressure shows low, replace fuel filter, test again.

3) If it still shows low, drop tank, inspect, probably replace the pump.

Bad ground? My 1997 Wrangler had tiny little battery cables that failed on me in similar fashion.

My 2000 WJ had a leaky battery terminal that corroded right through the positive battery cable and a bunch of local wires.

That's not what's going on here. I'm just saying it's a Jeep thing, and I understand.

I do agree that testing fuel pressure is Job One. No, wait, that's a Ford thing...

Better plan is to drive til it quits, then beat the bottom of the gas tank with a hammer. If that doesn't start it, check for spark.

When my '96 XJ had a failing CPS, there was no sputtering or rough running. It would just quit, like some one had turned the key to the OFF position

While it's sputtering, whack the bottom of the tank with a mallet or baseball bat. If it suddenly runs fine, it's the pump. I just went through this with my ZJ a few months ago.

I always enjoy troubleshooting techniques that basically amount to "hit it with a hammer". It's the only thing I miss about carburetors.

CPS will cause no spark/no fuel so keep that in mind as you troubleshoot. Same with the ASD relay.

a_aeschbury wrote: CPS will cause no spark/no fuel so keep that in mind as you troubleshoot. Same with the ASD relay.

Hmm... IIRC about how the JTEC PCMs work, crank sensor definitely causes no (or inconsistent) spark, but fuel is triggered based on the cam sensor in the distributor (so it might still get fuel with a flaky crank sensor).

Well the Jeep is now in my driveway, after trying to die twice on the way home. I've changed my mind on this being a fuel issue, as it seems to pull OK at WOT. Unfortunately, I bought the fuel pressure gauge prior to that revelation, so I'm still going to try it to rule that out. My money is now on the CPS.

Yup, fuel pressure checks out OK, right around 45psi. Works for me, much rather replace the crank sensor than the fuel pump.

Seems weird that the CPS would suddenly work at WOT.

FPR not dialing back from 45psi at idle/low throttle?

Fingers crossed the CPS sorts it, and you don't have to ponder next steps.

In reply to Furious_E:

Fixing bad grounds is usually free. Start there.

In reply to Woody:

Doesn't seem like grounds to me, no other electrical weirdness and everything remains functional when it shuts off. Should still take a look I guess.

In reply to Ransom:

It's not like I go WOT and all of a sudden the car works again, rather if it wasnt getting enough fuel it should starve and stutter winding it out.

Everything works fine until it doesn't, completely asymptomatic until the engine just cuts out abruptly.

I think I've replaced 75 CPS on 4.0L engines. I don't think more than 5-10 were instant off scenarios. They've almost all been intermittent or felt like it was starving for fuel. the top bolt is fun to get to BTW. Better see if a doctor can install the second elbow on your right arm....