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97 XJ cranks, no start

M

morelia1976

NAXJA Forum User
Location
Michigan
Need some help. I have a 97 XJ 4.0 AW4 that won’t start. It stalled once while driving a couple weeks ago, and I thought it was due to low gas. I put some gas in it, and then drove to my uncle’s to do some planned maintenance. We did the brakes, changed the front and rear diff oil, put on an aftermarket rear bumper, and it drove alright for a couple days, then started stalling again, while at idle and driving. After a few searches, I checked the battery and CPS, both bad, so replaced them and the TPS. Went for a short test drive and continued to stall.
Checked new CPS, bad, took it back and got a new one. Tested this one before installing it, cleared the codes, drove about 20m and it stalled again. Backed it up into my parking spot, turned off, and tried to see if there were any codes. Wouldn’t display any codes, even though I’ve never had problems getting 12 and 55 to display on my odometer and wouldn’t start. Let it sit for a little while and it started. Turned it off, checked for codes and got 12 and 55. Checked the CPS and read ~5V across B and C with my ohmmeter, so it’s bad. Again. That was Tuesday. Since then it won’t start, just keeps cranking, and won’t display any codes. I also found out the fuel pump keeps going as long as the key is on, it doesn’t cut off after a few seconds.
I figure it’s a ground fault causing my troubles, but I suck at electrical. Any help or guidance would be greatly appreciated. I also plan on checking fuel pressure, but am more worried about the wiring.
 
morelia1976 said:
So everyone else thinks its the aftermarket crank position sensor at fault?
Click to expand...

Cheap crappy "lifetime warranty" sensors ? No doubt. There are numerous threads that detail drive-ability issues that are cured with a genuine Jeep part, and faulty out of the box sensors from IdiotZone/PepBoys/Advance/O'Reilly's .

Genuine Jeep sensors are best, you can use NAPA sensors in a pinch.
 
Could be an ignition coil on it's way out too. Also, you "read 5V across B&C with your ohmmeter?"
 
I probably stated it the wrong way, but set multimeter to read resistance, put probes on the B and C terminals of the CPS and read about 5 volts (or ohms, or amps or whatever it's reading in). According to several sources, this is the proper testing method for a crankshaft position sensor. The reading should be for no connectivity. Thanks for the advice, I'll check the ignition coil as well.
 
Last edited:
morelia1976 said:
Would a bad CPS prevent any codes from being displayed?
Click to expand...

yes.

CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)


standard.jpg

.
standard.jpg



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.
 
and FYI...the fuel pump will continue to pump when the key is in the crank position. The short run is only when key is first turned to the run position.
 
Thanks for the info, the key is in the run position though. I'd turn key to run, then get out and put my ear next to the fuel tank. I don't really have anyone to help me on this, so there's no one else to crank it.
 
Update: MOPAR CPS installed, jeep won't start. Tested CPS with multimeter set to 2000, read 1584 ohms, bad again. fml. No spark, pulled ignition coil (big PITA to get to those nuts on back of bracket) and it tests ok as far as I can tell (it doesn't match the pictures in the haynes manual or online guides. Online Chilton guide has no pics.) Distributor cap, rotor, spark plugs and wires were all replaced last March when the motor was replaced. Used shop towel and small bolt to test for fuel pressure (sorry I don't have a fuel pressure gauge) and got a strong stream of gas.

Any thoughts?
 
Solved: Got tired of banging my head over this, took it to my buddy's shop. Mechanic found a short in the ASD power supply wire that was messing with the CKP and CMP.
 
ASD will shut you down every time if it's not up to snuff! Glad you got it resolved. Obviously your mechanic knew his way around the ASD system.
-----------------------------------------------------------------
Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.
 
Yeah, it only took him about 3 hours. It would've taken me 3 months of procrastinating and half-***ed searching to find it. I hate electric problems, but there's no escaping them without driving something pre-1970.
 
Follow on question to the replacement of the CPS....

I was at the VA 4WD annual run last weekend and had a few instances of "no spark" which were believed to be the result of a unhappy CPS. Consensus was that the CPS was getting too hot. Once the engine cooled, it woudl restart.

Folks on the trail said I would need a "Sh!T-pile of extensions to replpace the CPS, but the pictures I've seen don't look like connections that need a socket or anything like that.

Can someone clear this up for me?
 
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