91 Cherokee starts then dies right away

A

Alocatelli

NAXJA Forum User
Location
Maple Valley, WA
I already searched all over the forums and can't find an answer to my problem. Its a 1991 4.0L with auto trans. Here is the issue, it starts and runs for about a second or two then dies. The Jeep ran fine when I shut it off the other night and then when I went to start it yesterday it had this problem. My battery and my alternator are good. I am getting 39psi at the fuel rail, and my plugs are still firing while the engine dies. If I spray starter fluid into the throttle body the jeep keeps running as long as I keep spraying. I replaced the ECM thinking that was the problem and it changed nothing. Also jumped the ballast resistor with no change. I figure it has to be something with the injectors or the wiring. I am new to fuel injected cars and to jeeps so I am still learning. I am getting 12 volts at the first injector but only 0.12 volts at the last one in line. I have checked all grounds and they seem to be good. I also checked all my relays and moved them around and this also did nothing. Is there something I am missing? My fuel system checks out, it just seems that the injectors lose the signal to fire after about a second or two and the voltages seems funny to me but I really have no idea what they should be. Any help would be greatly appreciated on this as I am at a loss.:(
 
I could be wrong but you say you have fuel

pressure BUT do you have sufficient fuel flow.

I forget what the fuel flow rate should be.

Maybe someone who knows will chime in. Run a

search on fuel flow. There was a thread a while

back that fuel flow was talked about, could be

the fuel pump just isn't putting out enough

after the initial pressure and eng is running

out of fuel. Sorry I couldn't be of more help.
 
I will look more into the fuel flow issue and see if I can do a postive test to rule that out. It seems though that if it was a volume problem with my pump, I would see the fuel pressure drop off when the engine dies. The whole time it remains within the factory specs. If I test for voltage on the front fuel injector plug, I lose voltage when the engine stops running which makes it seem like the injectors are turning off. Although the voltage does seem to be screwy as well. I appreciate the suggestion and I'll see what I can find.
 
Alocatelli said:
I will look more into the fuel flow issue and see if I can do a postive test to rule that out. It seems though that if it was a volume problem with my pump, I would see the fuel pressure drop off when the engine dies. The whole time it remains within the factory specs. If I test for voltage on the front fuel injector plug, I lose voltage when the engine stops running which makes it seem like the injectors are turning off. Although the voltage does seem to be screwy as well. I appreciate the suggestion and I'll see what I can find.
Click to expand...


Check and replace the ballast resister on the drivers side fender, there cheap!
when cranking the power runs straight to the fuel pump(pressure normal). In the run position the power run thru the ballast resister and there to the pump.

replace it or put the wire back on it and it will keep running.


Flash.
 
I fully checked out the ballast resister and I think that is ruled out. I get good power across it and on both the wire leads going to it. I also tried bypassing it and just connecting the wires together and that made no difference. Also just went and re tested all the relays and they are good. I am at a loss on this thing.
 
Alocatelli said:
I fully checked out the ballast resister and I think that is ruled out. I get good power across it and on both the wire leads going to it. I also tried bypassing it and just connecting the wires together and that made no difference. Also just went and re tested all the relays and they are good. I am at a loss on this thing.
Click to expand...

Do ya have a fuel pressure gauge that you an hook to the shraider valve and watch crank and run pressure?
 
Since you are getting fire after it stalls out,

you can rule out the CPS and coil, The voltages

readings you are getting on the injectors are

puzzling. Could the TPS or an oxy 02 sensor

cause this. I personally think the fuel pump is

not keeping up with the demand for fuel. It

takes fuel, fire and air to run. Could it be the
AIC motor? If the TPS is fouled up, could it

cause a complete shut down of air AND do you

have Auto Shut Down? My motor home with a GM 454
had the oil pressure switch go bad and I had to

jumper the switch located on the oil filter

adapter. It would start then die right away

because the switch was saying NO OIL PRESSURE.

I hope it's something that simple. My 00 jeep

has the auto shut down. It would be nice and

also cheap if that is the problem.
 
Last edited:
Yes I have a pressure gauge that I hooked up on the fuel rail. I am getting 39psi initial and 31psi when I keep the engine running with starter fluid straight into the throttle body. After more fooling around I tried to just jump the fuel pump with power near the resister to see what would happen and my pump runs in the accesary position but shuts down when in the run position. I know my relay is good, but is there another relay inline that could cause this. Its interesting you mention the oil pressure because my oil gauge has never worked ever since I bought the Jeep. It has always read all the way over to the right. Could this be the possible cause, I know my engine does have an auto shutdown relay, wasn't exactly sure what it did. Seems strange though that for a year the oil sender has been bad and that it would all of a sudden decide to shut the motor down. At any rate I should get a new oil sender and fix that problem just to make sure.
 
Also of note is that I have scanned the computer and it shows no trouble codes. I know on OBDll systems you will get trouble codes for most sensors if they go bad, especially the O2, but I really don't know much about this system on my Jeep.
 
The auto shut down switch is a seperate switch

from the oil pressure switch and I'M not sure

where it would be located on your rig. Could be

anywhere there's oil pressure. There will be 2

wires on it or a pigtail with 2 wires, could

even have 3 wires.
 
If your talking about my oil sensor its down under my oil filter and only has one wire that goes to it. I know that sensor is not working but have a hard time thinking that could be the issue when it has been bad for so long with out any problems. Plus I went over the wiring diagram and the oil pressure sensor is not in line with the auto shutdown or any of the other wiring, it just goes to the gauge in the dash. Maybe that is what you were saying. I have ruled out the auto shutdown too because I checked for the proper resisitance, etc and it all specs out. Tomorrow in the light I am going to apply power from an alternate source directly to the pump and see if the jeep stays running. Thanks for all the help so far, its greatly appreciated :)
 
Alright I'll replace the ballast resistor just to be sure, thats easy enough, and I'll do a search to see how to test the map sensor....but if someone knows the drill for testing it that would be good to know incase my search comes up dry. I also already checked for vacuum and vacuum leaks and I think that is all good. I'll do these next couple steps and let you know what happens. Thanks.
 
Alocatelli said:
Alright I'll replace the ballast resistor just to be sure, thats easy enough, and I'll do a search to see how to test the map sensor....but if someone knows the drill for testing it that would be good to know incase my search comes up dry. I also already checked for vacuum and vacuum leaks and I think that is all good. I'll do these next couple steps and let you know what happens. Thanks.
Click to expand...



What year jeep do ya have? if its an older one........ya might want to see if the fuel filter, that is mounted on the frame, next to the gas take is plugged.

Remove it and blow thru it........if it take any effort,REPLACE IT. Even if it's not your problem, it could prevent one.


Flash.
 
You said the fuel pump runs when the ign switch is in the acc position but will not in the run position? Sounds like A IGN SWITCH problem now. When you put a direct 12v wire to the fuel pump and it works, Then it's probably the ign switch.
 
I'm leaning towards the ignition switch as well. If it starts up for a moment, the fuel pump is getting the voltage from the crank position, and continues to run until you let go of the key and it is in the run position. Try this at your own risk...just hold the key in the crank position, if it runs for 3 or 4 secs while you're cranking it...it's a bad ignition switch. Just my .02
 
sorry guys i didnt see a whole page of threaeds didnt know it was on in acc and off in "on" possition.wouldnt everything that should be "on" when ther ign sw was on also be affected?turnsignals for example? or how about heater fan?
 
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