jeep died

[giorno71]

first its a 94 yj originally a 2.5 - now a 4.o l h.o out of a 92 Cherokee, the swap has been done for a few years now, even drove it across Canada and not a problem till now.  i was driving to work and the jeep just died, no warning, no sputtering, just lost all engine functions, got it towed home and after work in the dark i listened for the fuel pump and nothing, thought i found my problem, then i noticed i had no check engine light when turning the key on. any ideas on what to check and how would be helpfull.  i have a spare ecu but don't wanna just plug it in in case something is frying it.



                                                                                                                                                                                                                                                                          thanks

[Dingleberry]

Sounds like a good place to start would be the crank sensor on the bellhousing. Had one fail on me before, gave the same symptoms.

[giorno71]

thanks ill be checking it out tomorrow, on the up side i have another running cherokee to pillage for parts, same 4.0 l h.o

[Nootch]

check all fuses, check the engine ground and body to frame grounds.

Does the engine crank?

did you check fuel rail for pressure? 

I had a no start issue on a 2k TJ when my cam synchro went and i lost the reference point for my cam timing and it wouldn't start. but it didn't quit on the road. just wouldn't start.

[mike s]

the crank and cam sensors are both common problems. if either fail, the often short out internally causing a short to ground. the PCM will shut off to keep from being damaged - 5V reference volltage goes to both sensors. thus no Check Engine Light

[giorno71]

thanks mike, i guess the cam sensor is next.  i swaped out the crank sensor and nothing, switched out the ecu and nothing, all fuses and relays are good the only fuse that was blown was the iod fuse, replaced it and nothing and the fuse didnt blow again

[mike s]

unplugging both sensors should bring the ECU back to life

[Dracitamo]

Have you checked the fuel rail for pressure as suggested by Nootch? This won't throw a code. (at least both times I've had problems with the pump, I've never had a code throw) This is a 10 second check. Just make sure you have a rag handy if you are going to test it.

It could be as simple as the wiring to the fuel module got disconnected or the hose connecting to your pump got disconnected inside the module or your pump died. If it's not sputtering I wouldn't say it would be your fuel filters as it will usually chug a little bit but never hurts to check. If you don't hear your fuel pump priming, that's where I would start.

[giorno71]

i checked the rail and no pressure there, as for the filter thats bran new less than a month ago. ill run my booster pack directly to the pump tomorrow and see if it works, and gonna try unplugging both sensors too. but when the yj was running i could always hear the relay for the pump when i turned on the ignition now i hear nothing and all relays r good,  but ill give it a go.  thanks for the tips guys  one question, is the cam sensor in the 4 l in the distributor ( magnetic pick up)? iv never had to replace one so not 100% sure

[Dracitamo]

If you have no pressure at the rail, trace it back to the tank. 

Check all your connections going to the tank as well. If they are lose, pull them apart and give them a little cleaning and shove them back together (click the little red switch so it locks) and then see if you can get some pressure.

If that doesn't help, then you might wanna drop the tank. I know dropping the tank sucks, but there might be lose wires in the module if you just replaced the filter. If you didn't connect the hose to the pump inside the module tight enough, you will lose all fuel pressure when you least expect it.    Or you might want to check the connection to the pump itself inside the module. If you haven't done a module before, it's pretty simple. Just remember where everything goes when you put it back in.

[giorno71]

all conections r good for the fuel pump and the pump works, no signal to the pump from what i can tell, tried disconecting the cam and crank sensors and still nothing and no engine light, have power after the ignition switch and have power and ground at the ecu harness and tried both ecu,s again and no start

[Bnine]

Start with the clutch safety switch if you arent having power from ignition. That ones pretty common. From there start checking ignition fuses and relays.

[Bnine]

Also if a tilt colum check the wires in there. Jiggle things around with the key on and see if there's any reaction. Another common issue with YJ/XJ steering ignitions.

[Nootch]

I have a sneaking suspicion that you have a bad pin on a connector or a broken wire somewhere.  I do not know the wiring personally for your model, but i know on the TJ all of the rear end electical comes up and makes a firewall connection on the center line of the engine.  Check for something similar and make sure all the pins are clean and tight.  You said the pump works with known good voltage, and that you swapped out the ECU.  That kind of leaves connectors and wires left.  A haynes manual and a good voltmeter with test leads will be very handy for this part.  BUT lets do a hypothetical on this.  you have the signal voltage for your pump only getting 1/2 voltage because of corrosion on a connector.  while  the ECU is sending the proper power, the pump doesn't have enough juice to start up anymore (motors take less to keep going that get going) of if there is an intermittent break in the wire that wouldn't be good either.


I trust you know how to properly use your digital multi meter, if not, let me know and I will reference you some great material for using it effectively. 

I know the pain you are going through.  I had to track down my reverse lights problem for 2 weeks before i nailed it.  Kept blowing fuses when in reverse.  Ended up being a dead short in the switch at the trans that would only be an issue when the trans was warm.  Weird eh?

[mike s]

Tackle the lack of a check engine light first cause that controls everything else. ASD relays are know to fail. The ECU turns the fuel pump on using power from the ASD relay. Ignition switch would be a good place to start