MORE '89 Jeep issues.

After replacing the crank positioning sensor, the thing started, idled, and seemed fine. I took it on a little test run and all seemed well. When I got back I shut it off and came back a few minutes to take a longer ride and it wouldn't start again. The fuel pump no longer worked at all and it had no spark. So I got out the stuff to test for injector pulse, got my brother to turn it over while I watched the light, and it started as soon as he cranked it. I had him shut it off so I could hook the injector wire back up and, when I tried to start it, no go again. Again no fuel pump. I let it sit a while and the fuel pump was working again about ten minutes later so I tried it and it reluctantly started, coughing and wheezing. I revved the engine a while, it cleared out and ran smoothly, so we took another, longer this time, test drive. It ran smoothly, had good power, idled at the lights fine, and seemed back to it's old self. I took it home, shut it off, went in the house about three minutes, came out to start it, and it again would not start. Again, no fuel pump. I didn't test for spark this time. It's been sitting about an hour this time and the fuel pump now works, but does not pressure up or something. As long as the key is on, I can hear the fuel pump running without shutting off. The engine will try to start, but just can't seem to get a handle on it. When I actuate the small valve at the fuel pressure test port, it has some pressure, but nothing dramatic. Any body want a Jeep?

 

check the crank sensor wiring and make sure its not to close to the exhuast if it is move it and use zip ties to secure far enough away from the exhuast to not get damaged.
the fuel pump shouldnt run all the time with the key on should just run for a second or two then shutoff if it doesnt see you cranking the engine over.

 

jeep pumps are known for "kinda" working. They will run just enough to tick you off. It sounds like you not only have pump issues but also a computer problem. I had a cam sensor in a cherokee generate a signal while the engine was koeo key on engine off. The computer thought it was running, I had tach signal etc.A quick test is to unplug sensors one at a time. If one shorts out it will kill injector pulse and fuel pump power. Good luck

 

bejay - If I find the wires damaged, have I ruined the sensor or can they be successfully repaired? Replacing that thing was a logistical night mare because I could see it but couldn't get a hand on it. The old one is still dangling in there because I couldn't get hold of it to pull it out of the clamp the wires are running through. I now may have a clue why the clamp, but no clue how to access it to hold the new wires back. I considered cutting an access hole in the firewall but didn't.

woodwrench - Sounds like a usable diagnostic method and, if the sensor doesn't turn out to be it, I'll try that. My suspicion is that bejay is onto it though. When I first got the new sensor in, the Jeep behaved correctly. With the key on, the fuel pump ran a couple seconds, then quit, and the Jeep started and ran fine with no problem. I let it idle a while to warm up for a test drive and it died while I was in the house. The issues got incrementally worse after that and now my symptoms are almost the same as they were when this whole thing started. The "incrementally worse" part leads me to suspect I was slowly burning through those wires and now have this problem.

 

it can usually be repaired if damaged all though may be hard to do on the vehicle but the sensor pigtail is usually long enough to remove any damaged area and be resoldered and heat shrink tubing applied over the repair.

 

Thanks. I'll let you know how it turns out.

 

Hey there!!!!........Sounds like we're in the right Church, but not quite the right pew.........As others have stated, be sure the exhaust has not compromised the wires....... 4.0s and 4.2s have a nasty tendency to break exhaust studa in the front and rear corners........escaping hot gases can cook the sensor wires quick........
Again..........IF the truck still has the C101 connector ( a BIG gang plug in front of the driver, front of the firewall) and the Crank sensor wiring leads TO it and FROM it, you need to remove the wires from said plug , solder and heat shrink them . The Crank sensor only produces about 1/2 volt A/C current on crank so ANY imperfection in the wiring can give you a no start condition.......After you are 110% sure the wiring is sound............Then start thinking ECU............

 

I've found no evidence of the gang plug. The wires go straight from the sensor to the wiring harness and the new sensor came wired the same way. Sensor, wires, weather pack connector, wiring harness. It doesn't go through anything else and appears to have been that way from day one, unless it goes through a fairly large wiring bundle and then to the gang plug. As far as exhaust gasses go, that's a distinct possibility. I do hear an exhaust leak at the rear of the engine and tightening the bolts didn't seem to have an effect. For the sake of preparation, I'm going to pull the new sensor and examine the wires to see if I cooked them. If not, what does the ECU look like and where is it located? The parts store told me it is about a hundred and a half, but didn't know where it was on the vehicle.

 

Under the dash alongside the center console if you look straight up you should see the ECU...........Aluminum square box about 1 1/2 inches thick .......and I would believe it should still read RENIX (renault/bendix)

 

OK, The wires to the crank positioning sensor are intact and don't even show signs of heat damage. I also checked to make sure the mounting bolts were tight thinking loose ones may mess up it's alignment and impede it's ability to do it's job. The Jeep will start and, until it's turned off, operates as if there were no problem. As soon as it's turned off, it will not restart and displays all the symptoms previously out lined. With time, sort of like a cooling down thing, the symptoms go away one by one until it will again start and operate until turned off. ECU? If so, is there a way to test it if I remove it and take it to a shop or does it have to be in the vehicle? Can I test it myself or should I just get a new one? Again I say, anybody want a Jeep?

 

Just an interesting fact. A friend of mine has an 89 Cherokee. That model year is the changeover year from Jeep to Chrysler. Makes it kinda fun to figure out which parts are Chrysler and which are Jeep.

 

Yeah, it's been a real pain. It seems everything about this thing is "special". I had a transfer blow up about two years ago with split case and all. It took ages to find one because this one isn't standard. It's "special". It's getting so the very word gives me the willies. At least now I've got a little better idea why. Thanks.

 

I took the Jeep on a fifty mile test drive yesterday and it behaved flawlessly, so I figured it's safe to post an update and thank you note. It turned out the last problem was the ECU. I replaced it late last week and have used the Jeep several times since, but only close to home. Being somewhat apprehensive about it, I didn't want that far to walk in case it stranded me. Yesterday was the "sink or swim" test run and I think all's well. Thank you very much to all who participated and for all the excellent information. I'm confident it saved me a ton of money.