My 90 Cherokee has suddenly decided to quit running! I have fuel to the pressure test port on the injector rail but the darn thing won't run after it cranks over and fires. Have tried to bypass the fuel filter ( broke down on the road) but am not sure how to begin to diagnose the issue. I wonder if it could be the Crankshaft Position Sensor??? Any ideas or help would be appreciated because I am LOST with this one!

 

Bill, check the connections on the fuel pump ballast resistor.

 

WOW! Don't know what the back side of the resistor is supposed to look like but mine has what looks like mud dauber or hornet mud built up around the connector and the resistor spring! I'm going to try to loosen it up and see if cleaning it up will help. If that doesn't help, I'll try replacing it! Let you know what happens and thanks for the help!

 

Can't find the part at Rock Auto or O'Reilly Auto parts. Any ideas where I can locate one? My Haynes manual doesn't even say a word about it!

 

No spark is a symptom of bad cps.

 

Just bypass it for testing purposes.

 

I had a similar issue on a 95 XJ.

Turn the key .... cranks, fires, but let the key go and it dies.

Turn the key ..... cranks, fires ..... SLOWLY bring the key back to run position until starter disengages and it keeps running ..... take hand off key and it dies.

BAD Ignition Switch.

To test theory I jumped " hot wired " the ignition switch.

Turned key ..... cranks .... fires .... release key ..... keeps running !!!!!

Ordered a replacement Igniton switch and they sent me the wrong part.

Ordered a second replacement ignition switch and again they sent the wrong part.

Dealer told me to give them the VIN number and they would order a switch and it would be the right one for $$$$$$$$$$$$

Installed a toggle switch for ignition jump and now the key is used solely for locking steering and cranking starter.

 

I checked out the Ballast resistor by bypassing it with a jump wire across the wires....no go. I guess the only thing left to do is replace the CPS. I've heard several say this may be the culprit. I am running out of money and, frankly, patience! Although yesterday was the first time this truck has left me stranded on the road (all the issues so far have happened in the driveway!) it's just a matter of time before I run out of luck AND patience. If i replace the CPS and it still won't run I guess I'll have it towed and let a "professional" take over the worries??

 

TEST things Bill!!!!

Go to my website and see how to do these things simply.

 

So it starts and runs, then dies when the key rotates back from "start" to "on"?

Might be the ignition switch, fuel pump fuse or wiring. You could check to see if there's 12V on the ballast resistor Cruiser mentioned with the key ON.
The start relay (below) bypasses that whole shenanigans when the key is in Start, powering the fuel pump directly from the relay terminal.
Once the key rotates back to "on", that relay drops out and power for the fuel pump routes from the fuse, through the ignition switch, to the ballast resistor then to the pump.

 

Alrighty then.....replaced the CPS and jumper the ballast resistor (while i wait on a new part.....zip, nada...it seems to WANT to start and runs for a nano second but....any other ideas? If not this one will be towed to someone who can figger' it out 'cause I'm out if ideas!

 

Test the fuel pressure yet?

 

Before I sent it off to anyone, I sure would be checking that .....

Ignition Switch

Fuel Pressure

I discovered the bad ignition switch by accident, as I was troubleshooting the same symptoms on my sons XJ.

A bad CPS and it won't fire at all ..... or it will fire, run and die.

I've have several bad CPS's over the years and none gave the symptom you described.