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Discussion Starter #1
Hey people,

I thought I would introduce myself with a troubleshooting question. I have been waiting for the weather to get a little better for what I thought was going to be a simple fix but so far I haven't figured it out.

'91 YJ 4.0L with multi-port fuel injection.

I have a no-start. I noticed that the fuel pump doesn't come on for its usual two seconds when the ignition switch is first turned on.

I jumped the connectors at the fuel pump relay and the fuel pump turned on and I heard the fuel flowing through the lines.

Bought a new fuel pump relay and installed it but no dice.
I am not sure exactly what the auto shut down relay does but I replaced it with the relay I had just removed from the fuel pump position just to try it out. Still nothing.

I jumped the relay connectors again and cranked the engine with the fuel pump relay bypassed and the fuel pump operating. Still no start.

Removed a spark plug and the cylinder was dry.

Checked the fuel rail very unscientifically (stuck the test port with a screwdriver) and got lots of fuel out.

Sooo... I am thinking I have fuel to the fuel rail but the injectors are not getting a signal to open. I imagine the issue is related to the fact that I am not getting that two second run of the fuel pump on initial start-up.

I suppose I need to get a real shop manual...

Any thoughts?:confused:

Thanks,

Britton
 

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did you check, or do you have a cps? if so you might check that.

Mike
 

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Britton,

I read your post and didn't see that you checked for spark. Fuel needs to be ignited. Have you checked the coil and distributor for power. Did you pull a plug and ground it against the block while someone cranked it over. You can get an inexpensive 12 volt tester to check for power to the coil and distributor
 

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Discussion Starter #6
CPS= crank position sensor, of course I should have figured that out.

I am under the assumption that my fuel pump not cycling when the key is turned on is related to the no-start. The fuel pump ALWAYS kicks in for about two seconds every time the switch is turned on so the fact that it suddenly has stopped doing it after a year of daily driving is what has me scratching my head. I am not sure what triggers the action but I bet it is related. It is probably time to get a real manual and figure out what is really happening here.

I haven't followed up the no-spark route because of the lack of fuel pump action and the fact that the cylinders are bone dry after cranking. This makes me think I am not getting fuel. If I were simply not getting spark then I would expect the plugs to be getting wet with unburnt fuel. To be thorough though I should probably eliminate that possibility.

Thanks.

-Britton
 

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Same problem as britton

the auto shut off relay was making a fast clicking sound after the jeep stopped running, the fuel pump works also, I have gas at and pressure at the test port, I do not have a spark from the coil. This has been a problem for a while, I would leave the key on for a minute and then the relays would click and the pump would run for a few seconds and stop and it would start right upand run great, untill I shut it off. If I tried to start it within a few minutes it work run great,leave it for more than a few minutes and I would have to wait for 5 minutes or more for the pump to start again. now it will not do anything. And by the way its a 1994 se with 2.5 Thanks Joe
 

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the auto shut off relay was making a fast clicking sound after the jeep stopped running, the fuel pump works also, I have gas at and pressure at the test port, I do not have a spark from the coil. This has been a problem for a while, I would leave the key on for a minute and then the relays would click and the pump would run for a few seconds and stop and it would start right upand run great, untill I shut it off. If I tried to start it within a few minutes it work run great,leave it for more than a few minutes and I would have to wait for 5 minutes or more for the pump to start again. now it will not do anything. And by the way its a 1994 se with 2.5 Thanks Joe
When my jeep started doing that I found it was in the distributor. The ignition control unit would start and run from cold, but would not restart after being driven. Eventually it just shorted out internally and left me stranded. They run around $35 and just plug and unplug.
 

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Discussion Starter #9
Just to put my issue to rest. After some work with the schematics it turns out my computer failed.

The fuel relay was not getting a ground from the computer. The computer also controls the 2 second fuel pump run before starting which had stopped working. Other options were a shorted MAP, throttle position, or distributor sensors that would have confused the computer. In my case the sensors were okay and it was the computer itself that quit.

-Britton
 

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Britton, Is the computer on the fire wall by the master brake cylinder? I have changed out the "cps" and still will not start. How much is a computer?
Thanks Joe
 
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