• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Need a clear explanation to test CPS

1

1904xj

NAXJA Forum User
Location
San Diego
ok to start off- 1993 xj, aw4, 4x4. 4.0 h.o.

so i have only used a multimeter once before. used it to test my CPS following these steps:

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 (See Image). 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.

so my multimeter only has settings for 200 and 20k. regardless i used 20k to test and 200. both times the meter only read .1

now if there IS resistance should it beep if the setting on the multimeter is set to it?

Does .1 mean low resistance and i need a cps?

what should it read for open (generally since all multi meters are different)

manual wasnt helpful, that is why im asking you guys.

please explain all of this to me like im 5.
 
What does your meter display for a reading when you have don't have the leads connected to anything? That is what it reads for an open circuit.

A reading of .1 is a low reading. Are you sure your meter is working? Test it against a known value of resistance to see if it measure resistance correctly.
 
McQue said:
What does your meter display for a reading when you have don't have the leads connected to anything? That is what it reads for an open circuit.

A reading of .1 is a low reading. Are you sure your meter is working? Test it against a known value of resistance to see if it measure resistance correctly.
Click to expand...

I'm also inquiring. What do we test it against. What would be a good source of resistance. Like a 10 year old PLEASE. I have a spare CPS off my 95 so I can bench test for practice!
 
Best test would be to measure a couple of different value resistors. You can buy them for next to nothing at Radio Shack. If you walk in with your meter, they may even test it for you for free.
 
If your testing in hopes of getting "0 resistance" just touch the 2 probe ends together. It should read no resistance.
 
ok so i meant it reads 1 when touching the cps. now when i touch the leads together itll read 0.00 now ive touched the cps with the black grounded and the red one touching both B and C. also connected one to B and the other to C. regardless of what i do the reading is still 1.

tested it on a battery got readings.
 
ok well the video allowed me to understand the multimeter more. but i still dont know how to use it with a CPS. i mean what should i get for a reading? should i get anything when measuring continuity?
 
I did a quick google search on CPS to see what they are. I suspect that our are called "inductive sensors." This means it's basically a coil of wire.

So testing resistance is valid to find out if the coil is (a) open (b) shorted or (c) some of the windings are shorted. The multimeter is used to measure the resistance of the long length of wire that's inside the device. This is why the range of the meter is important. Measure a good coil of wire on too high a range and it looks "shorted." Too low a range and it looks toward "open."

Low resistance equals "bad " according to the book suggests to me that the insulation protecting the coil windings from each other melts when the sensor is broken.
This reading would look like you just touched the multimeter leads to each other ("short")

You can test for a valid function of the meter by wetting your thumb and fingers of each hand and then pinching a test lead with your wet fingers on each hand. You're measuring the resistance from one hand to the other thru your body. The harder you pinch, the less the resistance. You'll probably not get a reading on the 200 scale and may start to get a reading on the 20k scale. (you'd surely get a reading on a 2M scale if there was one)

(yes, I'm an Electrical Engineer. But this is simple tech stuff.)
 
2X_01_Jeeps said:
I did a quick google search on CPS to see what they are. I suspect that our are called "inductive sensors." This means it's basically a coil of wire.

So testing resistance is valid to find out if the coil is (a) open (b) shorted or (c) some of the windings are shorted. The multimeter is used to measure the resistance of the long length of wire that's inside the device. This is why the range of the meter is important. Measure a good coil of wire on too high a range and it looks "shorted." Too low a range and it looks toward "open."

Low resistance equals "bad " according to the book suggests to me that the insulation protecting the coil windings from each other melts when the sensor is broken.
This reading would look like you just touched the multimeter leads to each other ("short")

You can test for a valid function of the meter by wetting your thumb and fingers of each hand and then pinching a test lead with your wet fingers on each hand. You're measuring the resistance from one hand to the other thru your body. The harder you pinch, the less the resistance. You'll probably not get a reading on the 200 scale and may start to get a reading on the 20k scale. (you'd surely get a reading on a 2M scale if there was one)

(yes, I'm an Electrical Engineer. But this is simple tech stuff.)
Click to expand...

As crazy as it sounds, people have actually died from touching a multimeter like that: http://www.darwinawards.com/darwin/darwin1999-50.html If you break the skin the resistance through your blood is very small and even a small current through the heart (from hand to hand) is enough to disrupt it.

As for testing the CPS I'm not convinced that's the best test method, or one really exists with a multimeter. I just swapped my failing CPS and by that test method it tested ok. I think its only once the CPS is completely dead and the Jeep won't start that this method would work. If you're having intermittent problems the CPS will probably test ok. I would try to rule out other sensors like O2, etc. and then replace the CPS.
 
figured out that "1" on this multi meter means infinite. so the CPS is good. anyways i solved my issue. it wasnt the cps it was the ignition coil. all good. thanks guys!
 
tdicola said:
As crazy as it sounds, people have actually died from touching a multimeter like that: http://www.darwinawards.com/darwin/darwin1999-50.html If you break the skin the resistance through your blood is very small and even a small current through the heart (from hand to hand) is enough to disrupt it.

As for testing the CPS I'm not convinced that's the best test method, or one really exists with a multimeter. I just swapped my failing CPS and by that test method it tested ok. I think its only once the CPS is completely dead and the Jeep won't start that this method would work. If you're having intermittent problems the CPS will probably test ok. I would try to rule out other sensors like O2, etc. and then replace the CPS.
Click to expand...

Is there a way to test the O2 sensors?
 
Boss Cherokee said:
Is there a way to test the O2 sensors?
Click to expand...

an o2 sensor generates voltage based on what the o2 measurement is.

Unless you have an o scope, or know how to backprobe the harness without screwing up the PCM, I would advise against it.

that said.

you need to backprobe the o2 sensor's voltage output wire. You must use a self powered meter. You should see a small amount of DC voltage.

under no circumstances try to test it's resistance, this will send current into the o2 sensor and that's a bad thing.
Most o2 sensors measure stoich ratio at about .5 volt. The number should vary slightly above and below this number.

if you want to pull the sensor and bench test it you can do so with a propane torch. Again, + meter wire to the voltage ouput, - meter wire to the sensor body itself, NOT THE TIP!. You'll get about .6 volts wth a propane torch after about 20 seconds.
 
Last edited:
I'd not heard of the electrician but.... having been in the Navy, and having had the job of Electrical Division Officer AND on submarines..... this sounds like something one of the guys would do.:-(

(Read the link. It's pretty entertaining.)
 
You must log in or register to reply here.

Similar threads

Anak
How to Slot the CPS
Replies
3
Views
118
souske
souske
S
98 XJ manual ignition problem
2
Replies
20
Views
4K
SurplusFan98
S
C
91 XJ missing at 2000 +rpm only when at operating temp
Replies
0
Views
1K
cptmiker
C
P
2K IDLE - Odd Shifting - TPS? (I know.. I know)
Replies
3
Views
2K
Unclewolverine
U
D
Probing solenoids thru TCM/fluid screwup?
Replies
2
Views
1K
DonQuiXJote
D
Back
Top