Atm3535

Hey all. So i went wheeling with my XJ last weekend for the first time. Did great accept for when I'm doing slow obstacles, the motor will just shut off and won't turn back on. The starter will just crank over and not start. after letting it sit for 5-10 minutes, it fires right back up with no problems. Then a couple minutes later, it will stall again. As soon as I start moving again, it does not do it anymore. I thought it was heat related because my AUX fan never turned on. I tested it this last week before going wheeling again this weekend, and it worked, so I just hardwired it to a switch so I could keep it on the entire time. Ran great and temp was below 200 the whole time. But towards the end of the day at AOAA on the double black diamond trial, it started doing it again!!! I don't believe its an overheating issue of the motor itself. I have a new coil on the motor, new plugs, wires, alternator, battery is relocated in the back. I know a lot of people say that it could be the crank sensor, coil, distributor. I talked to a guy up at Rausch Creek last week and he said it happens all the time because the fuel rail heats up and the gas boils. But the Jeep seemed cool this time. Any help would be greatly appreciated!! Unfortunately, I can't truly test it until the next time I go wheeling.

A side note to add, this weekend when I was trying to get it to start, I was cranking the starter, and all of a sudden, something reset and the motor stopped turning over while the key was in the forward starting position. I then let go of the key and tried it again and it fired right up with no hesitation.

cruiser54

What gauge wire did you use when relocating the battery?

Atm3535

4 gauge wire. Also forgot to mention that I replaced the fuel filter and have a brand new OEM Bosch fuel pump. Now that I think of it, it also does every once in a while falls on its face with acceleration like it’s sputtering but then goes back to normal.

'90Cherokee

My '90 did the same thing a few times while slow wheeling in AZ on a hot day a couple years ago. Hadn't done it before and hasn't again, still don't know what was causing it. Maybe it just didn't like being stuck behind slow people on the way to cold beers at the "Yacht Club" at the end of the trail.

When it dies does it shut off clean like you turned the key off or sputter to a death? Ever shut off while on the power or just at idle?

'90Cherokee

My first thought is the fuel strainer on the pump. If enough crud gets in/on the strainer it'll create a vacuum and at high temps the gas will boil creating a vapor lock at the inlet of the pump. It could also be pressed to tight against the bottom of the tank & do the same, but I don't know how these pumps are set up or if that could happen. Maybe if the tank is dented where the pump is it could cause that.

Atm3535

The fuel pump is brand new on the jeep so I doubt the filter is clogged. The fuel task doesn’t seem to be damaged at all either. It does seem like the jeep always dies when at idle while wheeling. The sputtering while driving though is always while on the gas and it eventually goes away after a couple seconds.

nolanbalzarini

what year is it?
On my 98 every once in awhile it would do the same thing. i bought a fuel rail insulation kit and a crank position sensor and it doesn't do it anymore.
I did both installs on the same weekend, so I dont know what fixed it.
If I had to bet, I would put money on the cps (for my situation, sound similar to yours).
you could try taking out the cps and cleaning it. if you dont remember the last time it was replaced, i would change it.
this is the one i did, fit and function 100%

the second issue you described sounds to me like the neutral safety switch. same story. clean it if you think it may help, or replace.

Atm3535

i think I’ll get a new crank position sensor just to rule that out and a fuel rail insulation kit. As for the neutral safety switch, it was an automatic and I did a five speed swap.

nolanbalzarini

maybe the computer needs to see that signal. or the starter was caught up for a second . im out of ideas.
i did the DEI insulation kit. i think it helps.
have you tried purging the vapors out of the rail when its acting up, there is a tire valve looking thing on the rail, poke it with something. make sure you try to catch the fuel with something and keep a fire extinguisher handy.

Atm3535

yeah I was thinking it could be something with vapor lock, but I would think that it would at least spit and sputter while trying to start it after it stalled. When I turn it over it’s like it has no fuel or spark.

'90Cherokee

Vapor lock in the pressurized parts of the fuel system is nearly impossible with a good working pump. Vapor lock on the pump's inlet can happen with a blocked inlet or faulty pump. Two small possibilities that come to mind are a blocked vent system causing the gas tank to go into a vacuum and a faulty fuel pump relay.

The NSS only effects cranking so toss that out.

Losing spark is most likely since you have a fairly new pump & screen.

I wish I'd done a spark test on mine when it did this. It's been years and hasn't had any issues, but it still bugs me a bit.