Electrical question

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  #1  
Old 01-11-05, 06:17 AM
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Electrical question

My daughter has a 1994 Jeep Cherokee 4.0 engine. When she took the vehicle out the other day it stalled and would not start back up. I checked for spark and had nothing at the plugs so we got it towed home. Once we got it home it started right back up again and ran fine until she took it out a few days ago and it stalled again and would not start again. By the time I arrived to the Jeep started again so home we came again. I extracted the codes even though the engine light did not come on and it gave me an 11 and a 12 which are battery disconnected and no voltage to the crankshaft sensor. My question is if it is a bad coil or ignition module would this trip the code for a bad crank sensor or is the sensor the likely culprit. According to the Haynes manual you can test the coil and the crank sensor but not the ignition module itself with a ohm meter which I have. However, if everything is fine now will it give me a bad reading? Or do I have to wait till it stalls again?

Thanks for any help,
Jay
 
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  #2  
Old 01-11-05, 06:41 AM
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Coils and crank sensors(another type of coil) can and do sometimes quit when they get hot and require testing when they are failed. The quickest test for a coil is feel it and see if its extremely hot. This does sound like a coil problem more than the module.
 
  #3  
Old 01-11-05, 07:23 AM
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intermittants are tough...

...and the best way to be sure you've found the problem, is to diagnose when it quits running. an ohmmeter is ok for some testing but a voltmeter is better and a labscope is best.

if your meter is a digital volt-ohm meter (DVOM) then use it...if it's an old analog meter (one with a needle) then don't use it...they are not sensitive enough and can damage computers.

crank sensors are pretty notorious for going bad on those and daimler chrysler says to test it with an ohm meter...disconnect the connector at the back of the intake and measure across the pigtail terminals (this is the end that goes to the sensor) B and C...infinite indicates a good sensor...low resistance indicates a failed sensor.

as for the ignition coil...measure across the primary terminals (these are the small wires)...you should get very low resistance (.95 to 1.2 ohm)

then measure across the high tension terminal (where the big wire to the dist cap comes out) to either of the small terminals and you should get a higher resistance...11,300 - 13,300 if it's a toyodenso coil and if it's a diamond coil then 11,300 to 15,300 ohms
 
  #4  
Old 01-11-05, 11:07 AM
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Thank you both for the help. I do have a digital meter and will check the Jeep out when or if it stalls. (It is running while I'm typing this). So it is not nessacerally the crankshaft sensor even though that number came up when I got the codes?

Jay
 
  #5  
Old 01-12-05, 02:58 AM
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chances are the crankshaft sensor is causing the problem. the computer will not store a code for it unless it has detected a problem in the crank sensor circuit. most likely the crank sensor is bad but there is a possibility the code could be due to faulty wiring on the crank sensor circuit or faulty pcm.
 
  #6  
Old 01-12-05, 05:00 AM
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Thank you for answering all of my questions. The coil checked out ok yesterday with the multimeter allthough it was running fine. I think I will start with the crankshaft sensor and and take it from there. I will post the results when I'm done. Thanks again.

Jay
 
  #7  
Old 01-17-05, 01:46 PM
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Just a quick update on my situation. I installed a new crank sensor 2 days ago and so far (knock on wood) the Jeep has been problem free! Thanks to all those who helped.

Jay
 
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