Jeep just shut off

'99 XJ 4.0L/AW4 140kmiles on it, driving home steady at 60MPH, and all of a sudden it just shuts off. No sputtering like lack of fuel, gauge shows half tank, and that seems correct as I filled it earlier in the week. All electrical seems fine, it cranks strong, radio, windows, etc. work fine. Pressed the schrader valve on the fuel rail it had some pressure. Fiddled with the CPS connector, pulled the coil wire, didnt have any spark while cranking. Swapped the fuel pump and starter relay, no change. I am not hearing the fuel pump buzz when I turn the key on. That is the extent of our diagnosis. I caught a ride home, grabbed the trailer and brought it home, and go over it more tommorrow.
The check engine light is not on.
I was thinking...
1- CPS
2- coil
3- fuel pump
anything else? what should I be checking? I have a volmeter and I think a fuel pressure gauge.

You are headed in the right direction. I bet my money on CPS.

If you have no spark I would look at CPS and coil for sure...mainly the cps. Maybe if you have a buddy with an xj see if he'll let you borrow it for 5 min. As for fuel pump did you ever hear it kick on before? Some of them can be rather quiet. And what do you mean you have a "little" pressure at the rail. Does it dribble, squirt or spray? From my experience they spray all over the damn place quite forcefully. If you aren't spraying when you press the schrader valve I would start by replacing the fuel filter because theyre only a few bucks and you probably need a new one anyway.

DrShaggford said:

If you have no spark I would look at CPS and coil for sure...mainly the cps. Maybe if you have a buddy with an xj see if he'll let you borrow it for 5 min. As for fuel pump did you ever hear it kick on before? Some of them can be rather quiet. And what do you mean you have a "little" pressure at the rail. Does it dribble, squirt or spray? From my experience they spray all over the damn place quite forcefully. If you aren't spraying when you press the schrader valve I would start by replacing the fuel filter because theyre only a few bucks and you probably need a new one anyway.

Click to expand...

you're right, I probaly need a new fuel filter. I am the original owner, its never been changed. I should know better, because I once swapped out a fuel pump on my MPI 4.2 CJ to no avail, only to find the filter was the culprit. But I could get it to run a bit, no power, sputtering, etc. Today was different...instant shut-off with no warning, and it won't even think about refiring.
I pressed the schrader valve for a millisecond and it sprayed all over, I didnt want to continue spraying gasoline all over Now that its home, I'll hook up the FP gauge.
I did used to hear the fuel pump buzzing for 1-2 seconds before I turned it over. Not today when I was on the side of the road. Thats another thing I'll check.
I think I have a used CPS from 95 XJ, I'll look for that. I put a 95 XJ engine in my 91 XJ, and the CPS connector was different. So when I put the 91 CPS on the 95 engine that I just dropped in the 91 XJ, I got to exerience the joy of swapping a 4.0L CPS in-vehicle. Is there anyway to check the CPS before pulling it out?

looks like 1991, 95, and 99 all use different connectors on the CPS

1997-01 the fuel filter is inside the gas tank, and is not routinely serviced unless pressure and flow testing shows poor delivery.

Start with the CPS.





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.

Typical 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.

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. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds and the ECM/ECU may behave oddly until you remedy this.

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.



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.

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.



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


1) 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 display correctly and/or the No-Bus is gone, replace the CPS.

2) If the CEL does not come on when the key is turned to the RUN position... then the CPS/CKP is bad.


3) 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.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is near the Transfer Case, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.



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 PROCEDURE 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.


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Thanks Tim!
quick check this morning shows the following...
fuel pump buzzes when key on...good
voltage and fuel gauge are OK, even when the CPS is unplugged
CEL never displays, even the CPS is unplugged

I feel confident enough to buy a replacement CPS now.

new CPS installed and I'm good to go.
used my 1/4" socket set (11mm socket) with the wobbler and 3-4 extensions. I wrapped the wobbler in electrical tape so it would wobble just a little, and not totally flop around.
I considered taking the front driveshaft out, but was able to work around it. Didnt have to drop the t-case skid plate.
The most difficult part was getting the 2 bolts back in. I did this from above, standing on a stool, I was able to hold the bolt with 2 fingers and a thumb, got them in. I was thankful, I'm not a large person.

This thread is just what I was looking for. My Jeep has been stalling for the past week and today I had to abandon it by the side of the road and walked home for another vehicle. Last night I replaced the Air Intake Controller sensor, which cost me 85 bucks at Napa. The old sensor looked bad with 155K miles so I don't mind the expense. I still have the stalling problem but today it would not start. I'll try the CPS next after the ohms test.

Update: Purchased the CPS from the dealer. Price was around 80 bucks. Installed the sensor using RenegadeT's suggestion, which was spot on, right down to the electrical tape on the wobbler (except I call it a universal ha ha). Engine started right up, no stalls, and ran fine. Great fix and easy to replace.