XJ wont stay running!

[AZTurtle03]

Okay guys...

The vehicle: 1989 Jeep Cherokee 4.0/AW4/NP242
Problem: Will not stay running!!! When I attempt to start the vehicle, it will fire up initially. However, it will just bog down and die after the first burst of life. If I turn the key all the way over and hold it over the motor will idle like normal, however as soon as I let go of the key it will die.

The things I have attempted so far:
2 new fuel filters
new injector O-rings
set TPS properly
fuel tank is clean
Verify that pump works (by tapping it directly to the battery)
all fuel lines have been cleaned and rubber lines have been replaced.
checked crank position sensor... did not replace but heard this should not be my problem
Replaced fuel pump relay.

Now I am lost... The vehicle started and ran fine about 2 weeks ago. I then have not drove it do to rebuilding the suspension. In that time I never touched anything other then the suspension. It just decided to be a pain out of the blue!!!

Suggestions?? Dynamite?? C4??

Thanks!
Turtle

 

[corbinafly]

Can you keep it running if you press on the accelerator?

Maybe check the IAC motor.

K

 

[langer1]

Bad Powerlatch relay or fuseable link.

 

[wulf711]

did the battery die recently? I had a similar issue, replaced alternator, charged battery and it ran fine. Just something to try.

Gabe

 

[Tally_XJ]

Mine did something very similar to this this week. Turns out, while doing some wiring and tune up stuff, I inadvertantly unplugged one of the connectors on the fuel pump ballast resistor on the drivers side inner fender. Its a white/offwhite colored ceramic thing about three inches long with two wires connected to it.

 

[old_man]

Just like TallyXJ put forward (nice post for a newbie :laugh3: ) what you describe is symptomatic of a bad fuel pump ballast resistor. Take a clip lead and short across the resistor. If it runs fine, presto you have your answer. It won't hurt to run it with the jumper. The resistor is to quiet the pump after starting.

 

[Tally_XJ]

Thanks for the "back-up" old man! I lurk a lot here but do not post much. There is already plenty of info here and not much need to post.

I bypassed my resistor instead of hooking it back up and I have noticed absolutely nothing negative from it, nor did the fuel pump seem to get any louder. Seems to be very safe to just eliminate it altogether.

 

[old_man]

Several years don't even run the ballast resistor.

 

[brtb]

Check the ballast resistor, mine was around 1 ohm or so.

If that checks out, compare the voltage at the pump between the ignition in Start and the ignition in Run. When the ignition's in Start, the fuel pump gets its power straight from the starter solenoid; when it's in Run, the power comes from the ignition-switched power.

My '88 had a very corroded wire splice in the big loom under the coolant bottle, where 5 red wires come together; start voltage on the pump was 13v, 'run' voltage which runs through that wire loom varied between 1.2 and 8.9 volts, depending on how wet the connection was. Undid the tape and lots of green stuff came out, not exactly the best conductor.

I'd grab an FSM and trace back the ignition-on fuel pump circuit, wouldn't be surprised if something corroded back there.