Crank sensor replaced
10-19-2011, 09:40 PM
#1
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Year: 1998
Model: Cherokee
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Crank sensor replaced
i got a 98 jeep cherokee 4.0 and was cranking but not turning it over, and after reading all over that most likely it was the cps, did it and nothing! wtf could be? 
10-19-2011, 11:35 PM
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Are you getting spark? So It's cranking, (turning over), but wont start? If you are getting spark try a shot of starting fluid in the throttle body. If that makes it fire you can suspect a fuel problem.
10-20-2011, 05:20 AM
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Good advice by Dflintstone.
The #1 sensor failure on the 4.0 is the crank sensor. However, there are quite a few possibilities for any no-start.
For a no-start, I always check for spark VISUALLY. It is absolutely the first thing I do. Sometimes you can have a weak spark, in which case a new ignition coil can be the ticket. A completely failed ignition coil can also result in NO spark. Coils can be easily tested for primary and secondary resistances.
Remove a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
The #1 sensor failure on the 4.0 is the crank sensor. However, there are quite a few possibilities for any no-start.
For a no-start, I always check for spark VISUALLY. It is absolutely the first thing I do. Sometimes you can have a weak spark, in which case a new ignition coil can be the ticket. A completely failed ignition coil can also result in NO spark. Coils can be easily tested for primary and secondary resistances.
Remove a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
10-20-2011, 05:41 PM
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Year: 1998
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Yea it cranks but no start, i tried the removing spark plug wire and had no spark while trying to start, guess i should try my luck and go for ignition coil?
10-20-2011, 06:03 PM
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Got a meter? I just saw this in another post;
>>>>Unplug your CPS. Probe both terminals on the sensor side. Set your voltmeter to AC volts. Have someone crank over the motor while you read the meter. You need .5 AC volts consistently or you can have intermittent no starts and/or poor running. I've seen new sensors fail this test. <<<
Also there is a fairly simple coil test.
>>>>Unplug your CPS. Probe both terminals on the sensor side. Set your voltmeter to AC volts. Have someone crank over the motor while you read the meter. You need .5 AC volts consistently or you can have intermittent no starts and/or poor running. I've seen new sensors fail this test. <<<
Also there is a fairly simple coil test.
10-20-2011, 07:40 PM
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just changed ignition coil hoping it would fix the problem. and still not luck. when i turn key before trying to crank it, it shows all the gauges showing how much fuel i got, batt level etc etc.
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10-21-2011, 11:34 PM
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so i had a guy come look at it, at first said it was the distributor but then realized there was no power going into dist to start, came to conclusion that it was the pcm after hooking it up and obd came up with that. if i install pcm do i need to take it to dealer to program it?
10-22-2011, 01:14 AM
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That fuse might be 30 amp, might be under the hood on the passenger side fender. Sorry I really don't know. Also I gather that the PCM will "learn" by it's self. Maybe up to over the next 40 hot/cold cycles.
10-22-2011, 05:35 PM
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are you both referring to same fuse?
10-22-2011, 05:41 PM
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i also just noticed that went i turn the key on, i hear a quick slight humming noise in the rear then it goes away. could it be the fuel pump?
