00XJ 4.0 wont start, STUMPED

Here's the background...

Over the last week noticed the rough idle on start after heat soak (last for 15 secs or so) has gotten worse, used to only occur when wheeling now started to occur around town . Yesterday decided to peak around a bit to see if anything obvious has changed (not expecting to find anything.) Pulled the coil rail to check a plug, looked great. Also pulled an the injector connector for the #3 cylinder with the intention of checking the injector resistance, the connector was extremely brittle and broke. Picked up a new connector at the dealership, removed the leads from the old one and installed them in the new one in the same position.

Here's the issue...

After all this the Jeep now refuses to start. It will crank but wont fire. Here's the diagnostics so far:

-Attempts to start with starter fluid, appears to have spark.
-Fuel pump works.
-Fuel rail has pressure, 40 - 45 psi.
-Swapped cam sensor, no luck.
-Swapped PCM, no luck.
-Swapped ASD, no luck.
-Injectors receive power when ignition is turned on (for a second or two then turns off) but do not receive power when cranking. (Verified on nearly identical XJ that injectors should receive power upon cranking. Also verified on the working XJ that power to the injectors for one to two secs with ignition on, until you crank, is normal.)
-Able to get power to the injectors while cranking by jumping the ASD circuit, however Jeep still does not start.
-All fuses in Power Distro box are good.
-Verified that power is getting to the appropriate Fuse slots from the ASD output.
-Attempted to test ground leads on injector connections but could not complete a circuit on this Jeep or the other running Jeep (tested while cranking.) Used a noid light feeding 12v power to the ground line on the injector connectors, maybe the switch happens too fast to show up on the bulb. Either way, test results were the same for both the running Jeep and non running Jeep.


As you can see Im quite stumped at this point, anyone have some good advice or suggestions!?

Did you swap the cam sensor or the crank sensor? Crank sensor (CPS) is on the tranny bellhousing, cam sensor (CMP) is in the distributor (or where the distributor would go).

Swapped the cam sensor.

Check the crank position sensor. Look at post #6 in this thread -> http://www.naxja.org/forum/showthread.php?t=969083&highlight=check+cps* for how to check it.

Edit: the connector for this sensor should be on the intake manifold, near the rear cylinder on the driver side.

You know, I was really putting off the crank sensor as it is kind of a pain to get to and I thought I wouldnt have spark if it was bad? Thanks for the push though, just swapped it out and she started right up!!!

Ugh, happy ending to a long weekend!

For everyone else - test the crank sensor before you swap it. I just went through it this week. It isn't too bad to get too. I recommend to remove the axle end of the front driveshaft and ziptie it up to the exhaust, it gives more room to work with and makes it easier to get to the 2 bolts on the tranny. Use a 12-2"4 swivel extension and a 11mm socket and you are good-to-go. Total time is less than 1 hour to change. Only use a Jeep OEM replacement part - do not use a part from Autozone, Kragen, Oreilly, etc - I spent a week chasing the problem because I used a crappy Autozone aftermarket part that was bad.

the_weirdo said:

Only use a Jeep OEM replacement part - do not use a part from Autozone, Kragen, Oreilly, etc - I spent a week chasing the problem because I used a crappy Autozone aftermarket part that was bad.

Click to expand...

I only use and recommend the Jeep crank sensor as well. I buy plenty of aftermarket parts, but have had mixed (poor) luck with aftermarket crank sensors. And even if they do work out of the box, the reliability/longevity doesn't compare to the Jeep sensor.