[1969AMX]

Good Morning, I've been away from the forum due to a lengthy deployment, but made it back and have been having issues with my cherokee. It's a 99 sport, 4.0, 118,000 miles. It turns over fine, but won't start. It ran fine from returning from deployment until now (3 weeks) Now it simply turns over. I checked the distributor and found all kinds of corrosion, so I swapped the cap and rotor for new with no luck. I then swapped the coil with the same results. After searching the posts here yesterday, I tried a few tricks, verified the Neutral Safety Switch is good, motor gets plenty of gas, however, again, no luck. The spark plugs were pretty worn, so I couldn't verify a spark, but even after closing the gap, there should've been some sort of spark.. Many have stated in other posts that the Crank Position Sensor is to blame, but after reading up in the ol' Haynes manual, it mentions that the CPS would affect the fuel delivery vice the spark. What do you think may be the issue?? Thanks for your assistance.

[1969AMX]

Also, there is no check engine light, all of the indicators and electronics seem to work fine...

[oakmckinley]

On my 2000 XJ I had a bad CPS and that's exactly what it did, cranked but would not start.
Before replacing it I would check the wiring for cracks, nibbles, etc.

[1969AMX]

Rgr, thanks, I'll swap out the CPS and keep my fingers crossed...

[XJH-007]

When you turn the key to the ON position, does the yellow engine symbol light up?

[CJ7-Tim]

The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when the engine gets hot, but works again (and will test as “good”) when it cools back down.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.



Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly and/or the No-Bus is gone, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start. Check the ASD relay fuse.

Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)



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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.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 – 275 Ohms. . If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

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[tjwalker]

My vote is the crank sensor. Follow Tim's lead above.

[Riley/MN]

Nice post Tim!

[VTEK1]

Tim must get really sick of posting that, he probably has it saved right on his desktop. hahahaha

[1969AMX]

Crank Pos Sensor was the gremlin afterall. I did see quite a bit throughout the electrical side that I really didn't like so after I swapped the sensor I went through and disconnected all plugs cleaned them, applied dielectric grease and reattached everything. Funny story about this jeep, I bought it from this Lebanese dude (seemed like a decent guy), so for the first few months I had that middle eastern inscense smell throughout the jeep. So, I put in about 30 "new car" air freshners to trump it. Well, it all wound up smelling like damned bubble gum.. I have no clue on that one....
Anyhow, much thanks for the inputs above, I am so far pretty pleased with this jeep and am looking into getting an MJ for a project in the future. (Thinking about doing an upgrade with late model cherokee parts...) Anyhow, currently restoring a 69 charger, so that's been vacuuming up most of my spare time.. Anyhow, thanks again for the assistance. Take care.

[1969AMX]

PS. Thanks Tim for the info, I actually found it on a different thread and printed it so I could follow it during the repair... Gracias Amigo..