How to test a Crankshaft Position Sensor? - JeepForum.com

 
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post #1 of 8 Old 11-02-2009, 05:24 PM Thread Starter
schwebel
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How to test a Crankshaft Position Sensor?

I have the manual to my 91 4.0 5spd YJ, and it says to test the resitance between A and B on the sensor plug. The plug is not labeled, it looks like three pins in a triangle formation. I unpluged it at where it connects above the intake manifold. Is this where I'm supposed to disconnect it from? Is there a way to tell which ones are A and B?

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post #2 of 8 Old 11-02-2009, 06:48 PM
Louie4
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I thought it was just a simple continuity test? But I'm not sure. I'll check my Haynes.

Lou

I have a jeep...and it is modified...I win.

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post #3 of 8 Old 11-02-2009, 07:13 PM
Apollo12227
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Not a continuity test... you test the resistance between terminals A and B which "should" be labeled on the sensor... You use a voltometer, set it to "ohms" to read the resistance...

Results should be 200 +/- 75, meaning, you need a reading somewhere between 125 - 275.... Any reading outside of this means the sensor must be replaced. (keep in mind the crank sensor works with an internal coil, its NOT a hall effect sensor like the stator/cam sensor... So although you may read the ohms as good, it does NOT mean that the coil is functioning properly [pulsing properly] while vehicle is running...

Also, you can check to see if power is comming to the sensor, force the probes of the voltometer into two of the three wires which go to the sensor it's self, and do a "dc" test to make sure your getting power to the sensor... you should read 12 volts when turning the key foward, a little more while cranking... There should be three prongs that go to the sensor, the one at the top is ground (i think) so use the left and right one..., the three make a triange with the flat plastic plate inside the connector being the bottom...

If you dont figure it out, tell us your symtoms and we might be able to rule it out.
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post #4 of 8 Old 03-08-2014, 07:52 AM
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I figured I would bring this back from the dead instead of starting a new duplicate thread.

My jeep died yesterday on the road. It just sputtered a little and the engine cut out. I determined I'm not getting any spark to the cylinders and ne spark from the coil. I got the jeep towed home and the first thing I did was unplug the CKS (crankshaft position sensor) and put my voltmeter across the B and C terminals and it had infinite resistance. I believe that means its not bad.

The next step is to test the CPS (camshaft position sensor). I suspect this may be the culprit because my distributor was making some noise back in November so I just wiped the inside down and shot some WD-40 on it. At the time it was our primary vehicle due to the others being down.

Is there an easy method to test the CPS? I've found some information on it but wasn't sure. If it is the CPS, should I just replace the entire distributor?

I will probably test the coil anyway to eliminate it. I have the values for that in my Haynes manual.

Lou

I have a jeep...and it is modified...I win.

YJOTM July 2012
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post #5 of 8 Old 03-08-2014, 10:26 AM
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I just got out to put a trickle charger on the battery after using the starter motor to get it off the road yesterday.

I check for voltage to the coil. I have 12 volts at the plug going into the coil. I'm not sure but I think if the CPS or CKS are bad it won't allow power to the coil. Hopefully someone will correct me on that.

I will check the coil resistance next...after I vacuum the house.

Lou

I have a jeep...and it is modified...I win.

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post #6 of 8 Old 03-08-2014, 10:56 AM
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My ignition coil values are:

Primary: 1.6 ohms
Secondary: 9.32 kilo ohms.

My Haynes manual resistance values:

Diamond - Primary: 0.97 - 1.18 ohms, Secondary: 11.3 - 15.3 kilo ohms
Toyodenso - Primary: 0.95 - 1.20 ohms, Secondary 11.3 - 13.3 kilo ohms.

Looks like my coil is bad but I'm not sure how to tell which one. Not that it matters since I'm out of range on both but for the replacement.

Edit: Forgot to mention my coil has a few cracks in it...weird.

Lou

I have a jeep...and it is modified...I win.

YJOTM July 2012
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post #7 of 8 Old 03-10-2014, 07:33 AM
Que89YJ
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The resistances aren't that far off but any time there is a crack it the coil you can have arc over and the coil needs to be repplaced.
Here is the crank plug diagram on this thread:
http://www.jeepforum.com/forum/f12/c...wires-1155751/
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post #8 of 8 Old 03-10-2014, 10:57 AM
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Quote:
Originally Posted by Que89YJ View Post
The resistances aren't that far off but any time there is a crack it the coil you can have arc over and the coil needs to be repplaced.
Here is the crank plug diagram on this thread:
http://www.jeepforum.com/forum/f12/c...wires-1155751/
Thanks Que. Excellent info. I got a new coil and it fired right up. My engine seems to have more pick-up and is more responsive.

I've attached some pics of the coil and where the cracks are. I couldn't see the cracks due to their location but I should have checked the coil out anyway given it's age and mileage. It's the original one.
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Lou

I have a jeep...and it is modified...I win.

YJOTM July 2012
YJOTM February 2014


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