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Shuts off while driving

C

ckowennos

NAXJA Forum User
Location
Nashville, TN
Ive got a 98 sport, 4.0 inline six, with an auto tranny that keeps shutting off while Im driving.

Friday, on the way to work it shut down on the interstate. The engine would turn over and everything else seemed okay except that it was like it wasn't getting fuel.

There was not very much pressure at the test pressure release valve on the fuel rail. I assumed this was because the fuel pump was not working so I dropped the tank on the side of the road and hooked a piece of loose hose up to the pump and confirmed that it was moving fluid. While I had it apart I replaced the two fuel filters because they looked pretty nasty and I had it apart anyway.

After I replaced the two filters, it started right up and I started home. it died after about a mile or two but it started right up again after only a few moments. Another mile down the road it died and I pushed it off the road, after about 5 min it started back up and I made it all the way home. (I assumed that it shut off because I forgot to prime the pump when I put it back together and that it was sucking air through the pump.)

It ran fine to and from work on Monday.

Today it died on the way home from work but it started right back up.

Just now I went outside and it ran for about 1 min at idle then died. I can hear the fuel pump coming on since it is quiet outside but there was still no pressure at the fuel rail and the engine would turn over but not start.

What do yall think is wong?

Intermitantly working fuel pump?
Clogged fuel lilne?
Water in my fuel?
Wet plugs or wires?
Incorrect idle speed?
Other?

Thanks,

Chad
 
Put a fuel pressure gauge on it. 49 psi + - 5 psi is within spec. If not, replace the pump.
 
ckowennos said:
... keeps shutting off while Im driving.......... the engine would turn over but not start......
Click to expand...

Failing CPS. Test it when it is in the failure mode. It may have thermal failure.



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)


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.

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.

.
.
standard.jpg

.
 
The NSS has always been an issue on this vehicle. I am used to having to wiggle the gear shifter to get the vehicle to start. It will usually crank right up if you pull back slightly on the gear shifter while turning the key. It was trying to start, the NSS won't cut off power to the fuel pump would it? I thought it would just cut off power to the starter.

My guages are kinda shoddy, but I know that it is because of my own fault. My fuel gage is messed up because I put the float in upside down when I was in a hurry to get off the side of the interstate. My oil guage is broken because I snapped off the sending unit when I was 16 and changing my oil. My voltage guage is working fine as far as I can tell.

My odometer/seepomoter does crap out everyonce in a while though but it usually comes back on when I bang on the pannel. Is that what you mean by a No Bus? Is this a big sign of a failing CPS? I assumed the speed was measued off the tire but that kinda makes sense that it would use the rms to calculate the MPH.

The fuel pump relay was the first thing I did after the jeep died on friday. And like I said, I could hear it turn on and run for a few seconds last night when it was quiet.

THANKS, I think I will try the CPS senson next. It makes sense to me that it wouldn't fire up if there was a miss timing between when the fuel goes in and the spark and whatnot.
 
Last edited:
Give the CPS a try for sure. With a bad CPS (they often are on the edge of failure and stop working when they get hot, thus letting the engine cool for a few minutes will make them work again) the ECU can't even tell the crankshaft is turning, so it doesn't trigger ignition at all.

I swapped my CPS on the side of the road in under 10 minutes yesterday morning, you can probably do the same seeing as you know enough to be able to dive in and drop a fuel tank on the side of the road. You'll want about two feet worth of extension bars and a U-joint/wobble joint along with an 11mm hex socket. If you lie under the vehicle on the driver side with your head about even with the front edge of the tranny bellhousing, you can reach up around the outside of the front driveshaft and put your left hand on the CPS bolts while feeding the ratchet up between the driveshaft and tranny, use your left hand to guide the socket onto the bolt and keep it there while you use the right hand to turn the ratchet. Remove the top bolt first and put it in last, make sure you don't drop it into the hole around the CPS (there is supposed to be a plastic shield in the hole but sometimes it falls out.)

You will also need a 10mm wrench or ratchet to remove the cable retention clip from the fuel rail / intake manifold but that's not critical, I was in a hurry so I just coiled the old CPS cable and CPS up and left them attached to the manifold and ran the new CPS cable right by it.
 
While a thermal failure of the crank sensor is fairly common, the fact that yours starts right back up without cooling down first makes me a little skeptical of thermal failure of the crank sensor or coil.

If your engine dies but will start right back up, then odds are by the time you pop the hood and get a meter on the crank sensor the fault is long gone.

Not all engine problems will give a CEL, but most will leave a stored code in the PCM so getting the codes read and posting up the ACTUAL numbers here would go a long way in helping to solve your problem.

Again, throw a fuel pressure gauge on it and post up the numbers.

Good luck.
 
NAXJA comes through again!!

Thanks so much for the information. I just swapped out the CPS and it fired up on the first try. The past two days, i couldn't get it to fire up at all, I think the old CPS had gone out all the way.

The advanced auto part was going to be about $80 but I went with the dealership part instead because yall have said the aftermarket CPS are crap. It kinda hurt to pay $124 at the stealership but if it lasts then it will be worth it. We'll see how this one holds up.

The GoJeep writeup was a big help too.

http://www.go.jeep-xj.info/HowtoCPSchange.htm


THANKS
 
I find that it's easiest if you lie under the jeep with your head right behind the left front tire. Reach up around between the front driveshaft and the frame rail with your left hand, then back towards the bellhousing, and use that hand to guide the socket and wobble joint onto the bolt head while you use the right hand to turn the ratchet. Feel for the plastic protective cover, if it's missing be very careful pulling the bolts. If you still have the cover, put the lower bolt in first during reassembly as it's harder to drop that one in the hole and the sensor will keep the cover in one spot so you can't drop the upper bolt in the hole.

I did this with the exhaust and transmission at operating temperature and did not get burned, you just need to use some care. The driveshaft helps keep your left arm off the exhaust downpipe.
 
Think my CPS is going bad again. It died on me again and I checked it with my new multi-meter.

I bought a mopar part from the dealership. Is there a better brand to try instead?

Is there something that would cause them to keep going bad?
 
I don't know what it is, but I just read another guy bought a BWD from advanced auto parts, and his CPS probs continued. He bought one from auto zone and now it's starting again.

I am having similar problems. I installed a CPS from advanced and it left me stranded for 20 mins that same day, so I put the old one back in. Still having the same probs. Might try the autozone one next, but can't imagine it's better than OE.
 
Just found the receipt from the stealership. I bought it on 10/4/10 for $124, the sensor died on 2/18/11. Four and a half months is kinda crappy. I've heard similar stories about after-market CPS failing but I figured the dealership one would be okay.

I looked up the warranty for MOPAR parts and there is none for electrical components.
 
ckowennos said:
Just found the receipt from the stealership. I bought it on 10/4/10 for $124, the sensor died on 2/18/11. Four and a half months is kinda crappy. I've heard similar stories about after-market CPS failing but I figured the dealership one would be okay.

I looked up the warranty for MOPAR parts and there is none for electrical components.
Click to expand...

If you have tested the new crank sensor and its bad take it, and the receipt, and go to the same dealer you purchased it from.

Warranty or not, that is too soon. If the parts department won't exchange it for you, ask to speak to the service manager or the dealership manager (owner/general partner/whatever). If still no joy, tell them you want to make an appointment with the factory rep, and insist that they give you his telephone number.

Please be polite, but FIRM. There is no guarantee you will get satisfaction, but it has happened before.
 
Sorry about bumping this thread. Just want to say that this post helped me immensely. Thanks for the thorough and detailed post.



Tim_MN said:
Failing CPS. Test it when it is in the failure mode. It may have thermal failure.



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)


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.

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.

.
.
standard.jpg

.
Click to expand...
 
CPS Grommet - Crankshaft Position Sensor

The dealership gave me a new CPS sensor today. I think that the plastic grommet may not be installed correctly. This would explain in my mind why the one I ordered from rockauto.com cranked once then blew out and why the new one does not work.

Does anyone have a picture of or a method to determine if the plastic piece is installed correctly?

http://jeep-xj.info/CPS7.jpg
 
The orientation of the sensor and the plastic shield is correct in the picture you have. The front of the vehicle would be to the left side, the rear of the vehicle is to the right.

I too have been going through CPS's like crazy lately (4 in the last 2 months) - my problem was due to a crack in the exhaust manifold that is heating them up and frying them.
 
I didn't run the engine long enough to heat up the last one. I know that it is in the hole in the correct orientation but I am having a hard time seeing/feeling to make sure there is the proper spacing between the grommet and the bell housing.

I'm getting ready to burn it to the ground.
 
Slip the part of the grommet that goes towards the front in first. There is a lip on the grommet that sits against the tranny. Then tuck the rear part of the grommet into the tranny. It may be slightly loose, but it is only to keep large debris out of the system.
 
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