Crank and no start?
03-02-2018, 06:22 PM
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Model: Cherokee(SJ)
Crank and no start?
First off forgive me if I posted in the wrong place as I知 new to the forum. I知 here seeking help with an issue a buddy of mine Jeep is having. His Jeep is a 2004 Jeep Grand Cherokee. Has the 4.0. I have never worked on one of these before or any Chrysler product for that matter. His Jeep has been having this issue for the past week or so. In the past week it has only started and ran twice for 30 seconds he says and then it dies. Other than that it just cranks over. The fuel pump does run when turning the key on. The ecm fuse is good as well. I ran my scanner on it and it was pulling code p0135 for the O2 sensor. I didn稚 think that was causing the issue but like I said I don稚 know jeeps. I tried to check the live data on my scanner while we were cranking the motor to see if any rpms were registering with the scanner but the Jeep doesn稚 support that with my scanner. That is an easy way I was told to check for spark. I wanted to check spark of coarse because at this point I知 leaning towards the crank shaft sensor. Any help with this is greatly appreciated. Thanks in advance.
03-03-2018, 12:15 AM
#2
Old fart with a wrench
Welcome to CF!
Yeah...I would suspect the crank sensor myself, especially with the 30 second run time. If it was the security system, it would only run for about 3 seconds or until it burnt the fuel in the rail.
When you turn the key on, the PCM (ECU) turns on the fuel pump to charge the rail with pressure, then shuts it off. When you start cranking, the crank sensor sends a signal to the PCM to turn on the pump relay and the ASD relay. The ASD relay controls the ignition and injector circuits. Without that signal from the crank sensor, it will never start. In my opinion what you're getting is a "once-in-a-while" signal that fails quickly. If you're really good, you can backprobe the crank sensor plug to see if you're getting a signal while cranking. It's a pulsing 5v signal. The plug is on the passenger's side of the block aft of the oil filter while the sensor is on top of the bellhousing on the driver's side. If you replace the sensor, my advise is to buy a Mopar one only. The quality of aftermarket ones suck!
Tell your buddy to buy a Haynes repair manual for his jeep and download the Full Service Manual from pacificcoastmanuals.com for $7.99. He and you should also check out wjjeeps.com
Of course, these are just my opinions.
Yeah...I would suspect the crank sensor myself, especially with the 30 second run time. If it was the security system, it would only run for about 3 seconds or until it burnt the fuel in the rail.
When you turn the key on, the PCM (ECU) turns on the fuel pump to charge the rail with pressure, then shuts it off. When you start cranking, the crank sensor sends a signal to the PCM to turn on the pump relay and the ASD relay. The ASD relay controls the ignition and injector circuits. Without that signal from the crank sensor, it will never start. In my opinion what you're getting is a "once-in-a-while" signal that fails quickly. If you're really good, you can backprobe the crank sensor plug to see if you're getting a signal while cranking. It's a pulsing 5v signal. The plug is on the passenger's side of the block aft of the oil filter while the sensor is on top of the bellhousing on the driver's side. If you replace the sensor, my advise is to buy a Mopar one only. The quality of aftermarket ones suck!
Tell your buddy to buy a Haynes repair manual for his jeep and download the Full Service Manual from pacificcoastmanuals.com for $7.99. He and you should also check out wjjeeps.com
Of course, these are just my opinions.
Last edited by dave1123; 03-03-2018 at 12:22 AM.
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