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Jeep stranded at camp in Moab - help ASAP

Jared

Jared

NAXJA Forum User
Location
Ogden, UT
Hey guys-

A friend just called up and said his bro-in-law's XJ won't start. It's a '97+, but I don't know the year for certain.

It has a strong battery and cranks over fine. There is no spark and no fuel pressure at all. I told him to start with the fuses and that my next guess would be the ignition switch.

Any ideas?
 
A bad CPS (crankshaft position sensor) will cause no spark.

Edit: I just saw the no fuel pressure, I don't believe that a bad CPS will cause no fuel pressure, but I'm not sure.
 
If it was running fine before and all of a sudden has no spark/no fuel, I would lean towards a CPS.

It's been rumored that sometimes on the 97+'s the voltmeter will not read anything when you turn the ignition on if the CPS is done. I don't know if that's true for all of the last gen's (or even at all)...just what i've read on here a few times.

You can also sometimes get away with unplugging the CPS and plugging it back in to get it to temporarily work again.
 
If the PCM does not get a signal from the CPS, it will shut down the fuel system.
 
Saudade said:
If the PCM does not get a signal from the CPS, it will shut down the fuel system.
Click to expand...

Well then I would go back to checking the CPS.

Use a multi meter, and test the resistance between the pins. If there is very low resistance, than it has shorted out, and you need a new CPS. I believe my bad CPS measured around 225 ohms, where as my good Jeep's measured around 650ohms.
 
New info -

1-Fuel pump relay is not functioning... I don't know if it's a bad relay or if there is just no voltage going to the relay. Obviously the fuel pump does not run, even during initial key-on position.

2-They have a code reader, which they have tried to use. They get "Link Error" repeatedly.

Given that multiple, independent electrical systems failed simultaneously and that the PCM is not responding to the code reader, my vote is for a bad PCM.

Any other thoughts?
 
Saudade said:
If the PCM does not get a signal from the CPS, it will shut down the fuel system.
Click to expand...

Hey, this info finally processed in my head. I called him and told him.

They have a '97 model auto with them and I advised they swap the known-good CPS to the not running jeep. I'll keep you guys posted.

Thanks for the responses!
 
As mentioned earlier you could try unplug/repluging the CPS harness at back of fuel rail. This should put the PCM into limp mode.

However, i'm not sure if that works on an OBDII setup like the earlier versions. It's certainly worth a shot as it takes 30 seconds.

You could also try swapping the fuel pump relay with the AC relay that should be right next to it. Look at the bottom of the power dist box lid underhood for the appropriate relay and location.
 
Looks like it was the CPS... it fired right up on the borrowed sensor. Add one to the list of failed XJ CPSs! There's a parts store open in town, hopefully the have the part.

Thanks guys!
Jared:patriot:
 
DeadEyeJ said:
Looks like it was the CPS... it fired right up on the borrowed sensor. Add one to the list of failed XJ CPSs! There's a parts store open in town, hopefully the have the part.

Thanks guys!
Jared:patriot:
Click to expand...

Glad to hear you found the issue. It's interesting when the CPS fails...without that signal the PCM has no clue what to do and freaks out shutting everything down.
 
CPS .... Oh wait youalready know that..... But yah with out the CPS signal, the factory shuts down.
Glad he's back up and running.
 
Seems that the inability to make a connection with the code reader is a common indication of a shorted (failed) CPS/CKP, as has been reported on this forum numerous times.
 
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