89 XJ 4.0L Cut off once warm (2-3 min)

Friends Mom's 1989 Cherokee 4.0L auto 165k died.
Any help / advice / thoguhts would be greatly apreciated.

I picked it up with the trailer this evening (Saturday) and took it home. The Jeep will restart once cold (2-3 hrs). Upon restart it will cut off after 2-3 min. Once dead, turn off ignition and attempt to restart~ engine turns over but no start. Spraying the inlet with start fluid will make it run (Poorly but run) a few seconds and cut off, Looks at first glance to be a fuel issue.

I checked the fuel rail shrader valve. No PSI with key off (I thought it should hold some pressure with a check valve at the pump). Good stream / flow once key is flicked and pump is on / running. First guess is that the injectors are loosing signal once warm.

If I understand correctly their is a crank sensor and a (distributor mounted) cam sensor. Which one of these fires the injector signal?

I have found a few articles refering to issues with cam sensor timing... I'd like to check the sensor and the cam sensor timing. Anyone got a link to a good write up on the subject? Does it sound like a good direction to go?


My intensions are to return to her house Wednesday with a Noid light to check for injector signal and a Fuel PSI tester + My code scanner and volt/ohm meter. I'd like to look at the signal from the crank and cam sensor but have not invested in a new Ocilla Scope wave reading style tool yet, I'll try and see what I can see with the Volt Ohm meter.

I've had a few people say throw a crank position sensor on it (As that often fixes a no run) but I find it unusual for the sensor to break down once warm & restart cold. Hope to check it with the meter soon.

:read: searching and reading

You need a pressure gage. Anything that would turn the injectors off like the CKP or CPS would also turn off the spark.
I would look at the fuel filter, ballast resistor or the pump. You need 31# to run and 39# at start up.

20# fuel pressure will squirt Petty good but will not keep the engine running.

When a Renix system first starts, it runs the engine based on stored information about mixures and such. Once the temp sensor tells the computer that the engine is warm, the computer switches over and uses the output from the sensors to determine the fuel mixture.

Your situation is a bit fuzzy since you say you are running way too lean, as witnessed by the start with fuel assistance. Nice troubleshooting 101 there by the way. I tend to think that it isn't a sensor. The reason being that 1-2 minutes isn't normally long enough to warm up an engine.

Try this. Start the vehicle and run it until it stops. Immediately check the fuel pressure, even by just pushing down the Schrader valve. If you don't have fuel pressure, we need to find out why. My first guess would be that the fuel pump ballast resistor located on the driver's side fenderwell may be heating up and going open. The good thing is that it is real easy to troubleshoot. Just unplug the ballast resistor and hook a short piece of wire in its place. The resistor is there mainly to quiet down the pump.

Post back your results.

unplug the vacuum line from the EGR Solenoid and plug it. Start the Engine cold and see if it cuts out in the time you stated.

Update:

Jeep will run 2-12 min. Now it is loosing Injector signal & spark.

Signal and spark will return once cool.

Fuel Psi is good. I couldn't find a cam position sensor.

Looking to change out the dist ignition module tomorrow.

I couldn't find a cam position sensor.

It's down inside the dist, below the plate.
The main thing that effects both the spark and injectors is the CPS, I would change that first.

I checked the crank position sensor individually for ohm reading and voltage in - out. I got the readings didn't change or differ when it would run / not run. I forget the readings now.

Another friend stoppedby and changed out the coil and module beneath it with a spare. (No change).

I'd rather test out and prove bad parts, but no decent manual.

Any one have a manual or diagnostic info for the 1989 Cherokee? I'd like to prove out the CPS and Dist module + read up on injecter signal.

whitfimb @ yahoo.com

I read in a search about a 5v referance pulse on a blue wire from the module. Can anyone verify it?

Thanks

The Renix system will continue to run with out a _Cam_ position sensor. The 91+ (chrysler) system will not. Check the _Crank_ position sensor's connector near the exhaust manifold. It can end up melting and cause your issue.

whitfimb said:

I checked the crank position sensor individually for ohm reading and voltage in - out. I got the readings didn't change or differ when it would run / not run. I forget the readings now.

Another friend stoppedby and changed out the coil and module beneath it with a spare. (No change).

I'd rather test out and prove bad parts, but no decent manual.

Any one have a manual or diagnostic info for the 1989 Cherokee? I'd like to prove out the CPS and Dist module + read up on injecter signal.

whitfimb @ yahoo.com

I read in a search about a 5v referance pulse on a blue wire from the module. Can anyone verify it?

Thanks

Click to expand...

There is no voltage in a voltage out.

The manuals on it's way.

Thanks,

Things are much clearer now.

Updates soon.

Repirs made:greensmok

Jeep is back up and running. BAd Crank Sensor.

Ohm'd out at 220 cold ran until cut off then read infinity.


I must have been :roll: :wierd: :speepin: last time I was checking it over.
Odd that it ran on starting fluid once it died when I check it on the side of the road. Inaccurate diagnosis can lead you around the barn the long way if you are not careful. Lessons learned.

BIG Thanks X2 to langer1 :thumbup:

I have a 89 xj that did the exact thing at 200,000 it would run for a few mins then shut off it runs great now though ..