JeepXJT

1991 4.0L Sport. Died while driving. used to start, for a few seconds, die. i made it home after it started and ran fine. woke the next day, started right up, ran fine, drove for about an hour, died. restarted about 15 minutes later, drove for an hour or 2, turned the truck off, started back up, 10 mins later, died. never started again. Got towed home.

List of New Parts:
Plugs
Wires
Coil
Cap
Rotor Button
Distributor Pick-up
Crank Position Sensor
Fuel Filter
ECM
Battery

the only code is 12 (battery/ECM recently disconected)

I have checked for loose wires
I am getting Spark
there is no Catalytic converter to get clogged
the fuel pump activates with the key on
fuel pump primes the system in 2-3 keys turns

I originally thought the injectors were not pulsing which is why i replaced the ECM. but when that didnt change anything, i tried starting fluid. still no attempt to create combustion in any cylinders.

I am dying here. its been down for months. i have a volt meter, but dont know much about using it. someone please help.

BuckB91XJ

ECM doesn't give your jeep it's injector pulse. The Crank Position Sensor does (CPS) generates the spark timing and injector pulse timing when commanded to by the ECM....and yes, they are known for going bad. It's located at about your 2 o'clock position on the driver's side of the bellhousing. A couple of bolts and an electrical connector and it comes out. A little bit of a PITA but, you can do it.

BuckB91XJ

Whoops guess I need to get my glasses checked. I just saw you already did that.

BuckB91XJ

I would definitely go with the fuel pump. You can have fuel at the fuel rail and you can hear it buzz when you turn the key on. I had this same situation on my 91 XJ 4.0. The only way to properly check the fuel pressure is to put a hand held gauge on the test port on the fuel rail. Your 91 XJ has to have 30 +- 1 PSI or the fuel pump is bad period. If your reading is even 2 PSI away from 30 your fuel pump is bad. Trust me on this one. I learned this lesson the hard way...lol. Hope this helps.

xjguy71

It is poss you got a bad crank position sensor. Do u have fuel at the rail when u depressirize the system?

JeepXJT

I've got spark, and I have tried spraying fuel/starting fluid directly into the throttle body. If it was the fp, wouldn't spraying directly into the intake create combustion? Bad CPS would mean no spark, correct?

xjguy71

If u sprayed start fluid it should at least sputter. Do u have fuel in the fuel rail when u press the stem?

fallenknight308

Fuel Pump

JeepXJT

Zero sputter, fuel is in the fuel rail. When I sprayed starting fluid in the TB absolutely nothing changed. Tried gas in a spray bottle too.

xjguy71

Id try a new cps.

JeepXJT

Still nothing. New cps, fuel pump, filter, all ignition, ecm, battery. All relays are good, turns over strong, does not attempt ignition. Plenty of fuel, fuel pressure, spark. Only codes are ac clutch circuit, ac dosnt work and it hasn't for years. And it throws cooling fan circuit relay. I checked it, its good, should still start. Yet no

blinkbears

Bad ground somewhere?

JeepXJT

Would a bad tps create a no start condition? If so, why no tps code 24?

BuckB91XJ

If you are getting Spark and dumping starting fluid straight into the throttle body like you sayand getting not even a sputter, the only other thing it could be is that your engine is so far out of time that it won't start, but even then I'd figure it would sputter. Are you ABSOLUTELY sure you are getting spark?? If it isn't even sputtering when you dump fuel or starting fluid in it, I'd say you couldn't possibly be getting spark....or at least getting it all the way to the plugs.

JeepXJT

I can pull the number one plug stick it in the wire boot, have Kim turn the motor over, while I ground the plug. There be sparks. And as far as timing, it ran just fine after the first two times it died. Turned the key off. Then back on, bump,bump,vroom, away she goes. Got on the interstate, 70mph, then its like I turned the key off. No unusual noises or combustion. Just off. Never started again.