XJ starts then stops after a second

I have had a recurring problem with my wifes car. Its a 1998 XJ sport.
The problem is, every now and then the car refuses to start for her. It will start then run for a second and the stop. I know it did it the first time and stopped starting altogether, it would just keep on cranking over. I had a mobile mechanic look at it, it cost me 200 dollars and he could not fix it. The battery went flat and after a few weeks it started just fine.
It stopped yesterday and what I have done the last few times (a couple of months apart) to get it running is to reset the PCM internal memory as per GoJeep website.

I am mechanically minded and do all the work on our cars. I am more interested to find out if there is something else sending a bad signal to the PCM to cause it to malfunction. I have replaced the cps as a precaution but still did it a few months later.

Are you sure your barking up the right tree? Next time check for spark during the episode, if there is spark and your injectors are ticking then walk around to the back reach down and smack the fuel tank really hard. Go back and turn on the ignition but dont try and start it...just listen for the fuel pump, after it shuts off (about 2 seconds) do it again, and again.

4th time try and start. If it fires right up after that then you need a fuel pump.
My buddy is a car dealer and I help him all the time with his xjs. If we have one that wont fire (but has spark )we try that more than 3/4th the time thats the problem. When we get it back to the shop we pop on a new filter/regulator/check valve (Yes they are servicable 98+, and advance auto has them) If that does not solve the problem we put a new assembly in and use the regulator on the next one.

Jackal1979 said:

.......stopped starting altogether, it would just keep on cranking over. ......

Click to expand...

Failed CPS is the most common reason for a cranking and cranking no-start.


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 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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intermittent problems are always the most fun!

When in a no start condition you need to determine the missing element: fuel, air, spark, compression.

Lets a**ume that because it does run that you have compression. As you have compression, then the engine is probably sucking in air. That leaves us with two possible missing elements: fuel and spark. Ok, you can check the fuel pressure at the rail and listen for the fuel pumps operation. Next, purchase a NOID light so you can determine if the injectors are getting a firing pulse from the PCM. What about spark? Buy a cheapo plug, and when it won't run pull a spark plug wire and put it on the cheapo plug, ground the plugs body to the engine, then with the key crank the engine and look/listen for the spark.

Once you have determined the missing element it is fairly easy to isolate the problem in that particular system.

Last thing--have any anti-theft devices installed?

Thanks for the replies,

When the mobile mechanic looked at it he checked for fuel, spark, injector pulse and all were good. He did no more than i could and he had no answer for me.

When the car died on my wife, I drove to the car, verified it still would not start (well starts then stops after a second), disconnected the positive terminal, grounded it on the alternator body for 30 secs, reconnected battery. Then i turned ignition key to 'on' position, turned on headlights, turned off headlights, turned off key.

Then i started car as normal and walked away knowing it was going to stay running.

This has happened the last two times. So I would suspect this would rule out the fuel pump although I will keep it in mind.

I will do more fault finding next time it won't start, to see what is missing.