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Will not start when hot.

K

ktwalker01

NAXJA Forum User
Location
Jackson, WY
Hey guys I searched for a good bit for a similar thread but found none with no success. Here is the story this is for my moms 96 XJ 4.0L 2wd 4dr AW4. Her car has an issue where it will start cold no problem and then will run and run and run like there is nothing wrong. The second it is turned off after it has been driven around for over 10-15 minutes it will not start again. So lets say she drives to the store she gets there fine, and comes back to her Jeep 5 minutes later she cant leave until a good 1.5 - 2 hours of waiting.

Things it does after its heated up and is being attempted to be restarted.
Fuel Pump primes, starter has no trouble etc etc but the motor will not turn over.

When it is running from a cold start the XJ has ZERO issues run great no check engine lights or anything.

Any ideas??

Thanks
-K.W.
 
"Motor will not turn over' means that starter is not spinning the engine.

"Starter has no trouble" means that starter cranks good.

Is the actual situation that the motor is spinning good, but does not want to start running even though it is cranking good on the starter? or other?

Most likely guess is Crank Position Sensor. Abbreviated CKP, but also CPS. You need to check for spark. CKP is known for heat sensitive failure. Search for crank position sensor and you will find MANY threads. It is the most common XJ failure.

When it is cold, you could heat it up with a hair dryer and see if that makes it not start. Then cool it with cold water and see if it WILL start.
 
Last edited:
Cranks, No start. The CPS can fail hot. Check to see if the tach shows RPM during cranking. You can also pour water on the CPS to cool it off and most times it starts but replace it soon. It's in the bell housing on the driverside. You can see it from the engine compartment at the rear at the bell housing.
 
Cranks but no start.

Its the se ghetto edition with the giant fuel gauge and speedo no tach. Ill order a new cps and see if that fixes it. I was wondering if that would be it but I am getting no check engine and I wasn't sure if that could be a problem with a hot start. Thanks! Ill let you know how it goes.
 
What you are describing does sound like "thermal" (heat related) failure.

Crank sensor is a possibility but here is another. The camshaft position sensor.

You describe the problem as running fine UNTIL the engine is turned off, then no start until cooled down.

If the cam signal is lost while the engine is running, the PCM will calculate spark timing based on the last cam signal and the engine will continue to run. However, the engine will NOT run after it is shut off.

So because of the way this one is acting (running fine until turned off), I'm suspecting the cam sensor even more than the crank sensor (which normally will kill the engine once it gets hot, not wait until you turn it off).

Both cam and crank sensor can be tested but you'd want to test it when it's in a no-start condition. Testing it when it is running okay may be of no value.

Good luck and post back what you find...
 
Well thanks for the handy info for the other cps (camshaft position sensor) that is known to fail while hot but not be critical until a hot start. So now im searching for this piece online and am having a lot of trouble i understand this thing is called a lot of things from camshaft position sensor, stator, sync-pulse generator, and sync signal generator. I am having a heck of a time finding where these would be for a 96 4.0l model. Any ideas?
 
Ohh sorry what I ment if anyone knows where I could buy this darn thing? autozone, advance auto parts, and napa dont seem to have it and i cant really find it online.. and i would love to avoid the stealership.
 
ktwalker01 said:
Ohh sorry what I ment if anyone knows where I could buy this darn thing? autozone, advance auto parts, and napa dont seem to have it and i cant really find it online.. and i would love to avoid the stealership.
Click to expand...

rockauto.com

STANDARD MOTOR PRODUCTS Part # LX236
MoreInfo.gif

w/o Plate
getimage.php

$49.79


napaautoparts.com: ECH MP831 Price
Unit
:
:
58.99
Each
autozone.com

might be part number CR142

HAVE YOU TESTED the sensor???
 
The crank sensor is more common, the only failure I've seen on the cam sensor (distributor pickup) was when the dist was bad and was hitting the sensor. While replacing both or other parts may work for most people I tend to prefer diagnosing the problem and replace just what's failed.
 
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If you replace everything, you may well be replacing good parts that were made in USA 10 years ago with Chinese parts made now. And your parts are time tested. ELectronics have high infant mortality.

Thanks, birchlake for the distinction on hot restart vs. hot failure to run. That is an important insight. CKP failure will be to not run more than not restart! I would consider throwing a CMP cam postition sensor at this if I was a part replacing type instead of part testing.
 
winterbeater said:
If you replace everything, you may well be replacing good parts that were made in USA 10 years ago with Chinese parts made now. And your parts are time tested. ELectronics have high infant mortality.

Thanks, birchlake for the distinction on hot restart vs. hot failure to run. That is an important insight. CKP failure will be to not run more than not restart! I would consider throwing a CMP cam postition sensor at this if I was a part replacing type instead of part testing.
Click to expand...

I would buy a $3 NOID light instead of the $50 synch-sensor and check it when it is in a fault condition. Of course, I am one cheap SOB. And good point on the infant mortality rate of electronic components and import vs. USA made items.
 
Do a search on heat soak. There was a TSB on the problem.
 
Could also very well be the check valve in the fuel pump. I've had two Xi'an that would fire up great when cold but would have to either prime the fuel rail with a couple key turns or pedal to the floor. Have you tried priming the pump/key trick?
 
You know I just experienced this problem myself..figured the battery was shot but i cleaned out the connector for the CPS and bam...starts up fine.
Could be an easy fix!
 
okay update, this is a xj I got for my mom to use so its been on the back burner when it comes to my free time so I have little to none to mess around with it and I appreciate the input you all have given me. When it comes to the temp sensor the jeep will start without it even plugged in. and I get a code when its unplugged so I am going to rule that out. I figure sense it is going to be her car I just might go ahead and spend some money and replace every sensor on the engine it is a 126,000 1996 4dr se I dont know the previous history of the car but I have already gotten her suspension re done, along with the bearings, bushings, tires, radiator, hoses, and water pump. I dont want this XJ to strand her hehe the exterior and interior is of show room quality and i got it dirt cheap thats why i picked it up.
 
check yoru starter

When its hot..and barely wants to crank...get underneath it and tap the starter with something and have someone turn it over..if it starts right up then the solenoid on the starter is bad...replace the starter
 
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