Gorf

On my 1991 Cherokee Laredo (4.0), I have recently been having some fuel delivery issues while at idle or just off idle. Here's how the story started:

I was reading my ecu one day and noted the failed o2 sensor that it logged. It had been a while so I changed the O2 sensor out. Within a couple days I started having my first problems. After being driven for a while (more then say 20 or 30 minutes) the idle will slowly decrease while in drive at a stop. If I give it a little gas it hesitates as if out of gas then will roar to life. If I am moving just off idle and it does it, I can actually get some pinging and afterfiring that is very indicative of a lean situation ie: no fuel.

Well from some reading here and elsewhere online I thought that it might be an Idle Air Valve stuck. Ok says me, so I replaced it. Problem still occurs. So then I figured I would throw a new fuel filter at it. Problem still occurs. I then had a fuel injection service done on it at a local shop (it needed it anyway), but still the problem lingers.

So here I am stuck. I guess the only thing that I haven't touched is the fuel pump. Anyone have any ideas or suggestions?

ZachsXJ

Sounds like a clogged pre-filter in the tank. They tend to filter out pretty fine particles and if you get any significant amount of dirt in the tank they will clog. I had this happen to me a while back, it was annoying as crap...next time it does it try pulling over and turning it off, let it sit for 5 minutes and then start her back up. With mine that would make it go from bucking and being un-drivable due to being so lean to almost running normal again.

Gorf

ooo now there was something I didn't think of. The pre-filter. These Jeeps are all in-tank filters with attached prefilters I assume?

98 JeepJeep

Check fuel pressure.......you may have a clogged pre-filter,Pinched line,bad/Weak pump or faulty regulator.

ZachsXJ

Yours has TWO filters, the in-tank prefilter that is on the intake of the fuel pump and then an inline filter that is outside the tank and located directly over the rear axle on the inside of the frame rail. I'd replace the fuel filter as its probably the original one(for some reason NOBODY replaces them) and if that doesn't change anything then take the fuel pump out and see if the pre-filter is clogged.