96 2.5 runs great, then doesn't

My 96 2.5 XJ sat in a pasture for about five years. The fuel became a solid, but fortunately there wasn't much left at that point. I ran a 90 model sending unit for a while until I was able to repair the original with a new pump. I put a Carter pump in the tank with a new screen, and replaced the filter. I've been about three thousand miles since then, with no trouble until the other day. It started to hesitate, then it would pop when you gave it the throttle. Idle was fine, cruise was okay, but it was as if the TPS wasn't reading WOT or something. Next day, I stopped for a filter and a new screen. It didn't start in the parking lot. Ran just as bad after replacing the filter, but got me where I was going. There, I replaced the pump again. Problem solved, ran like new. For a day.

Now, it runs like nothing is wrong for about ten or fifteen minutes. Then, it begins to hesitate, a little more, and dies for a second or so. It'll do that like clockwork from that point on. I notice a bit of hesitation around and over 3k rpm, as well. It only seems to quit when I'm cruising or accelerating. It dies every minute or so, but comes right back, and runs fine again.

I want to say the pump was the cheapest you could get from rockauto. I ordered it for a piece of rubber I needed, and set the rest aside. At $20, I have little faith in the replacement pump. The screen on the other pump came out looking fine, but the contents of the fuel filter were not good looking at all. Quite black, pouring from the tank side. I initially diagnosed it as a vacuum problem, and replaced the injector o-rings. I then leveled the intake with a big bastard and replaced the gasket. Once assured the intake was tight, I moved on to fuel delivery. Fuel at the rail looked perfectly clean.

So I've ordered the fuel pressure regulator from Amazon. I'm going to purchase a Delphi pump from a franchise I'm not going to mention here, because they offer nationwide lifetime warranty replacement, but their service is the worst. You already know who it is.

My rail has no valve to install a pressure gauge.

I'm posting here because I need this Jeep to run all of the worst trails in the Guadalupe Mountains this weekend. Otherwise, I may chance it on a 90 which followed me home yesterday and I know pretty much nothing about. Any help is greatly appreciated.

Thought I might add, the only code it registered was lean condition indicated a couple of times. In the last two days, no check engine light.

Have you replaced the fuel line or cleaned it?

Nope, have not done that. I believe the crud has finally dissolved to fine enough particles to be drawn into the pump, and short of replacing fuel filters regularly for a while, I can only imagine resolving it by changing the tank for a clean one.

I'm not experiencing anything which would indicate regulator failure, other than perhaps limited fuel pressure at WOT, but I wonder if replacing will only result in the contamination of a new part? I mean, it goes tank>pump>fpr>filter.

I solved my problem for the time being with a 90 Laredo. Has anyone else experienced multiple fuel pump failures such as this from crud in the tank?

I'm now pretty well convinced that it has something to do with the purge system. I dropped the tank after noticing that a vacuum line up to the vent valves seemed loose. The rubber bushings in the tank were a loose fit, so I shored them up with several wraps of teflon around the valve. I have yet to put fuel in it in order to see if it made any difference, but I'm thinking that if the problem remains, it'll be a vacuum leak somewhere beyond the purge valve.

I'm also considering bypassing the purge valve to see if it affects the way it runs.

Just a thought.....next time it starts acting up, try removing the gas cap. You might not be venting correctly and getting a vacuum in the tank.

Well, I actually improved the seal a bit when I dropped the tank, so it's worth a shot. I put five gallons in it and checked it out. Same thing. Tried disconnecting the purge vacuum. same thing. Plugged, same thing. Flipped, same, so I replaced it with a known good unit, and it did the same. It did register some codes, though. It's showing P0138, P0441, and P0141. This was before I went messing with the vent valve. It kind of points to O2 sensor failure up front. I couldn't figure out which fuse was for the O2 heater circuit, so I tested them all.

I guess I'll try a sensor and get back with my results. I think I have a good one around somewhere in a box.

Not much change. Runs deceptively well for about eight minutes, then dies and starts the same thing all over again. It did seem to improve highway performance ever so slightly, but the fact that it's dying like it was leads me to believe it was not the problem. Then it was raining.

Could a crank or cam sensor act like this without throwing a code? My 96 four door was similar, but it had nearly 300k an about half an inch of slack in the distributor shaft. No code, but I don't remember any hesitation. It would just quit.

old_man said:

Just a thought.....next time it starts acting up, try removing the gas cap. You might not be venting correctly and getting a vacuum in the tank.

Click to expand...

I'll be damned if this did not work. No codes yet, either. What's additionally strange is that I stopped, tightened the cap, and had the problem return immediately, but it remained after stopping to loosen it back. I had stopped for fuel when I left the cap loose and drove around for a good half hour, even on the Interstate.

I replaced the strainer, regulator, and filter all at once, and the problem seems to be resolved. I expect to have to replace the tank, however. I had a good look inside it after removing a fairly laden strainer, and it has a lot of rust. The cavity where the regulator fit was full of it.

I stopped by the local gasket shop and had them make me the washer which was missing from the regulator from Crown. Had two cut, one in 1/16" and the other in 3/32" Viton. The 1/16" fit like the original, which was toast.

I also ordered a pair of NTK O2 sensors, which should come in tomorrow. More power, better economy, and no more check engine light.

Thanks for all the suggestions. I was looking for a pressure test adapter when I was pushed into the need for the truck. I hope it can swing an 800 mile road trip before I have to replace the tank.

Well, that lasted a day. Half a day at least. I replaced the sensors and it got worse. Flat worthless. I could hold the pedal to the floor in neutral and it wouldn't clear 2k. Lots of popping. Couldn't drive it. Fortunately, I picked up yet another strainer on the way home. Swapped the tank for a shiny clean one, installed my assembly with the new strainer, and it's like nothing ever happened. I can red line it through third and it runs great, no loss of power. I think this time it should stay resolved.

As a warning, the Crown regulator O-rings are cheap neoprene and will swell if you remove your regulator once installed. I found more crap in there, and replaced the new, one day old rubber.

I know, nobody cares.

1500 miles later and still no problems, no check engine light. The only thing I can imagine is that the flow was impeded by the crud in the tank, which would accumulate within a few minutes of driving, and settle back into the tank when parked.

I did immediately notice that I have to crank it twice to start, like the regulator is faulty. I'll be putting the old one back in as it never exhibited a problem.