CoffeeCommando

So there I was, just driving and it shut off on me. I got it pulled down the street to a friend's house and it sat for about 2 hours before we came back to test out the fuel pump idea by priming it. It started up, but I had a suspicion it could be something else (not for any good reason). I was wondering if it just sitting and cooling down might have had something to do with it. Regardless... it was due for a fuel pump replacement at 190K.
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.. so I replaced the fuel pump. The old pump primed to 35 on the first key on and that isn't enough to start it. With the new pump, it actually primes to 52 on the first try, and it runs at 62 PSI constant while driving. It's a Carter fuel pump and I had heard good things about them and Bosch.

I drove it home and within the first few minutes of driving I noted a faint amount of hesitation. After about 17 minutes of driving (that's about how long I drove it when it shut off on me the first time), it shut off again. Only this time, it kicked back on within 5 seconds, then shut off again a few seconds later, then did that cycle one more time before finally shutting off for good.

I had a spare crank sensor with me I had bought at O'Reilly's and had used before (I took it off and put the OEM one back in there a few months back while doing a flywheel replacement for no particular reason, other than when testing the magnetism the OEM part was way stronger). It took me about 20~ minutes to get it swapped out, then it started up and I finished the rest of the 3 minute drive home. During that short drive the rpm's had a bit of waver according to the tach at steady speeds that I hadn't noted before, and I suspect maybe that's the O'Reilly's crank sensor.

Any ideas as to what this might be? I ordered a MOPAR crank sensor and a SMP camshaft position sensor. The cam sensor that's in there now (AutoZone brand of some sort) I had taken out about 4 months ago. The jeep would start to run very rough and have no acceleration while running at 17-18+ AFR's after it had been on for a while. I thought it was a matter of engine bay heat causing it to malfunction, but the morning I replaced it when I started it up cold it barely ran. I figured the heat cycles finally toasted it. It went back in when I did the flywheel change 2 months ago because I damaged the other one one I indexed the position with an Allen key and forgot to take it out while turning the engine over to tighten down the torque converter teeth. I was expecting problems from the second I started it up with this unit being put back in there... but there were none and it drove for months without issue.

At the time I had taken it out I didn't have any under-hood heat relief and it got too hot. I now have the hood spaced up about 1.5 inches in the rear to let it vent though so that could be the reason it didn't act up for so long. I suspected heat being the problem initially because I know neodymium magnets start losing their magnetism at 175F, and I am sure that little unit probably gets that hot since I didn't have a gasket or spacer to keep it from touching the engine block. It's a shiny silvery magnet so I know it's neodymium, and it's a weak one too which doesn't help matters. The old ceramic magnets aren't as strong lb for lb but they'll hold their magnetism up to 300F.

Anyways, those are my suspicions. I'm just curious if anyone has had the exact symptoms of the engine cutting off and on before not turning back on, and if so what it was you had to replace. This one is a first for me.

dzywicki

Sounds like a crank position sensor problem to me. Classic failure mode after it gets hot. Cools off and then runs again. The Cam position sensor will cause some odd running problems as well. I only use MOPAR or Eichlin (NAPA) for those 2 sensors. I wouldn't trust any house brand from any of the major auto stores.

CoffeeCommando

I don't know if this is common for MOPAR in recent history of older parts, but I ordered the MOPAR crank from RockAuto and it was made in Mexico. The SMP cam sensor looks sturdy and it had the heart symbol on it in RockAuto which is why I ordered it. It wasn't a remanufactured unit like the A-1 Cardone units.

CoffeeCommando

It wouldn't start, so I pulled out the O'Reilly's crank sensor and swapped it with the MOPAR. It started up. The O'Reilly crank sensor magnetism was so weak it wouldn't stick to anything. The MOPAR would hold itself on to metal.

I had swapped the cam sensor as well but forgot to take note of the position of it. I took pictures of the angle and position of it with the cap off, but then swapped caps for curiosity with the new SMP part (this was before the crank swap) and lost track of the position. I finally put the whole new one in there, and when I swapped the crank it started... but it would idle at 1000 RPMs and wouldn't rev past 1700 without stumbling down to below idle and shutting off. It ended up being the cam sync sensor I put in needing re-adjusted. Once it was in the right position it went right to a 750 idle and no hesitation and stumbling.

On a side note... while that was in there in the wrong position I got these codes: P1391 Crank Sensor, P351 + 352 + 353: A + B + C Ignition Coil Primary malfunction. I cleared the codes to verify they came back. Having that sync sensor in the wrong position lit up all of those. I assumed they went away after I got it set right since it ran flawlessly. I know I've read in posts people say it's not used and you can unplug it after the jeep is on and it'll run without it. One thing is for certain, if it's in the wrong position it will certainly give you problems driving.