Won't start when hot
#1
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0 High Output
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I got my XJ about 2 months ago. First thing I did was replace the fuel pump and put new wheels on it. It ran okay for a bit then started turning off at random times. I found the crankshaft position sensor wiring to be the culprit there. Some of the wires were melted and the copper was exposed. Now it has developed a new issue that I'm having trouble diagnosing. It will turn on ok and run fine as long as you don't turn it off. If you turn it off after running for more than a minute it won't turn back over. I've been trying to time the cooldown on it, but so far it looks like it takes over an hour to cooldown from just a minute of driving. Any help diagnosing/fixing this issue would be greatly appreciated.
Thanks for the help
Thanks for the help
#2
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Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
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OR are you trying to say that the starter engages normally and the engine goes round and round, but the engine won't run?
If it's the latter, test your CPS. Could be your ASD relay, too.
#3
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Year: 1992
Model: Cherokee (XJ)
Engine: 4.0 High Output
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Thanks for the advice. The starter engages normally, the engine just will not run. I tested the CPS as described in the video and no issues there. I checked the ASD and it also appears to be fine. I'm not sure where else to look to find the issue.
#4
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Year: 1996
Model: Cherokee (XJ)
Engine: 4.0 I6
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Well you explained you replaced the fuel pump on the side of the tank, but have you checked your fuel pressure regulator on the end of the fuel rail? The regulator can cause strange things to happen when it is on its way out.
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BlueRidgeMark (12-03-2020)
#6
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Year: 1998
Model: Grand Cherokee (ZJ)
Engine: 4.0 L6
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In the video, his last check was the Hall-Effect sensor generating an AC voltage when the engine is turned over. His meter shows a .02 VAC at rest ( not unusual ) and when he turns the engine over the meter shows a .01 / .02 VAC generation. He then says you want to see a .05 to 1.0 VAC being generated ( his meter should have shown a .07 to 1.02 VAC gain)
He then says the sensor is good? He never says what the no spark problem is/was.
Is a .02 VAC gain normal for a good running sensor? Or is the computer just looking for pulses?
Unless there is an inverter in the sensor, he should be seeing a DC voltage as the magnet on the flywheel passes the Hall-Effect sensor as the flywheel spins?
He then says the sensor is good? He never says what the no spark problem is/was.
Is a .02 VAC gain normal for a good running sensor? Or is the computer just looking for pulses?
Unless there is an inverter in the sensor, he should be seeing a DC voltage as the magnet on the flywheel passes the Hall-Effect sensor as the flywheel spins?
Last edited by Rapidrob; 12-03-2020 at 10:09 AM.
#7
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
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In the video, his last check was the Hall-Effect sensor generating an AC voltage when the engine is turned over. His meter shows a .02 VAC at rest ( not unusual ) and when he turns the engine over the meter shows a .01 / .02 VAC generation. He then says you want to see a .05 to 1.0 VAC being generated ( his meter should have shown a .07 to 1.02 VAC gain)
He then says the sensor is good? He never says what the no spark problem is/was.
Is a .02 VAC gain normal for a good running sensor? Or is the computer just looking for pulses?
Unless there is an inverter in the sensor, he should be seeing a DC voltage as the magnet on the flywheel passes the Hall-Effect sensor as the flywheel spins?
He then says the sensor is good? He never says what the no spark problem is/was.
Is a .02 VAC gain normal for a good running sensor? Or is the computer just looking for pulses?
Unless there is an inverter in the sensor, he should be seeing a DC voltage as the magnet on the flywheel passes the Hall-Effect sensor as the flywheel spins?
My money says bad crank sensor for the OP. Buy a cheap one and see if it fixes or changes the problem. Just beware the quality of the cheap chinese ones is questionable and its possible get a bad one out of the box.
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