[Lone Star XJ]

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).

[PITBULL1967]

Sounds like there's too much resistance. Lo means there's an open in the circuit.

[Lone Star XJ]

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.

[Lone Star XJ]

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.

[CJ7-Tim]

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.

.

[Lone Star XJ]

Originally Posted by CJ7-Tim

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.

[Lone Star XJ]

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.

[CJ7-Tim]

Originally Posted by Lone Star XJ

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.

[Lone Star XJ]

Originally Posted by CJ7-Tim

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?

[CJ7-Tim]

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.

[Lone Star XJ]

Well, I am going to go ahead and put the new one on and see what happens. I will report the results.