New Crank Position Sensor bad? - JeepForum.com

 
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post #1 of 13 Old 05-27-2009, 08:08 PM Thread Starter
Lone Star XJ
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New Crank Position Sensor bad?

I am still chasing a cyl. 1 misfire. I checked the resistance of the crank position sensor and it read 7.25 Mohms. It would just read .0L ohms and the same when set to kohms. I bought a new sensor and checked the resistance of it. It reads 4.96 kohms and also .0L ohms.

Is my meter jacking with me or what? This is on a 1997 XJ, so the resistance should show 0 ohms (ie. open).

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post #2 of 13 Old 05-27-2009, 08:29 PM
PITBULL1967
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Sounds like there's too much resistance. Lo means there's an open in the circuit.
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post #3 of 13 Old 05-27-2009, 09:01 PM Thread Starter
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That is what I thought. However, this new one has me puzzled. I guess I will go back to the parts place and check another one.
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post #4 of 13 Old 05-28-2009, 09:11 AM Thread Starter
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I went out and checked the sensor this morning after the engine had cooled all night. It was giving me an open reading, 0L. I checked the new one again and it still read 4.96 kohms. I drove to work and checked the resistance again and it was back up to 7.6 Mohms. I am convinced that my meter is giving me an 0L reading when set to ohms and kohms because the resistance is out of range. My meter only reads up to 400 when set to ohms and either 4, 40 or 400 when set to kohms. So I took the new sensor back and ordered a new one. I will give an update when I receive it and check the resistance.
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post #5 of 13 Old 05-28-2009, 09:21 AM
CJ7-Tim
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The CPS would not be responsible for a single cylinder misfire.


CPS TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C. Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

.

.

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post #6 of 13 Old 05-28-2009, 10:02 AM Thread Starter
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Quote:
Originally Posted by CJ7-Tim View Post
The CPS would not be responsible for a single cylinder misfire.


CPS TESTING PROCEDURE 1991 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C. Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

CPS TESTING PROCECURE for 1987 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

.
Thanks Tim. I have been following your test instructions from another post. I didn't think the CPS would be responsible for a single cylinder misfire, but I am trying to go through and test/check everything I can before replacing parts or ultimately taking it to a shop. The resistance changing on me between it sitting over night and when it is warm seems odd to me. I am going to get the new sensor at lunch and check it.
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post #7 of 13 Old 05-28-2009, 07:24 PM Thread Starter
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This should be very simple, but it is driving me nuts. I guess there is something to having the meter set in the 1k ~ 10k range. I don't know why it would mater if you are using a multimeter with an auto range function. Both the old and new sensor read about the same resistance when cold. The resisance of the old one does change after running the engine.

I just tried test #2 in Tims post. I set my meter to the 4 AC volts range which reads down to three decimal places. I had my wife crank the engine and I am only reading 0.006 ~ 0.007 AC v. I am going to say the one on the Jeep is bad and needs to be replaced. I hope this does the trick because it is an expensive part to replace for no reason.
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post #8 of 13 Old 05-28-2009, 07:44 PM
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Quote:
Originally Posted by Lone Star XJ View Post
The resisance of the old one does change after running the engine......
Take careful note of the range of model years for the two different testing procedures. The cut-off is the difference between OBD-I and OBD-II. You can only get useful results from the test that is for your year of Cherokee.

If one of the CPS you have shows resistance when warm, I suspect that one as starting to fail. The CPS can have thermal failure where it is bad when hot, and tests OK when cool.

.

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Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ...

Originally Posted by Ronald W. Reagan: Government is not the solution to our problems; Government is the problem.
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post #9 of 13 Old 05-28-2009, 08:02 PM Thread Starter
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Quote:
Originally Posted by CJ7-Tim View Post
Take careful note of the range of model years for the two different testing procedures. The cut-off is the difference between OBD-I and OBD-II. You can only get useful results from the test that is for your year of Cherokee.

If one of the CPS you have shows resistance when warm, I suspect that one as starting to fail. The CPS can have thermal failure where it is bad when hot, and tests OK when cool.

So soing the voltage test on a 1997 is of no use?
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post #10 of 13 Old 05-28-2009, 08:17 PM
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I have replaced the CPS on 3 out of 5 of my Cherokees when they failed and the engine would not start. Only one gave me warning by behaving erratically, the others just failed. I am not a Electronics Tech, but there are major differences between the OBD-I and OBD-II self diagnostic systems.

.

A recent Gallup public opinion poll shows the NRA, at 58% approval, has a higher approval rating than either Hillary Clinton or Barack Obama.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ...

Originally Posted by Ronald W. Reagan: Government is not the solution to our problems; Government is the problem.
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post #11 of 13 Old 05-28-2009, 08:39 PM Thread Starter
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Well, I am going to go ahead and put the new one on and see what happens. I will report the results.
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post #12 of 13 Old 07-13-2012, 08:09 PM
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Quote:
Originally Posted by CJ7-Tim View Post
The CPS would not be responsible for a single cylinder misfire.


CPS TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C. Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

.
I know this thread is old. But, I did a search before posting. Give me credit! What is low resistance? Mine is 3.69 on a 1997 XJ

'97 Cherokee, 99+ intake, 62mm TB, 703 injectors (new), k&n intake, Hypertech III, 180* stat (1/8" drilled hole), 2.5" manifold 2 tail pipe (Hooker Maxflow & hi flow cat), Perf header, 4.5" zone lift, 32" GY Dura Trac, Rear head rests. Comp cam "231" & Perf head (LS1 BIG valves 2.02/1.62). 3 row alum radiator.
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post #13 of 13 Old 07-14-2012, 03:53 PM
CJ7-Tim
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Place your meter in the correct test mode settings and touch the probes together. Note the display. Now test your CPS. If you get any reading that is different than just touching the probes together, the CPS is probably faulty.

.

A recent Gallup public opinion poll shows the NRA, at 58% approval, has a higher approval rating than either Hillary Clinton or Barack Obama.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ...

Originally Posted by Ronald W. Reagan: Government is not the solution to our problems; Government is the problem.
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