cps diagnose

Is the crankshaft position sensor one that gives symptoms or does it just fail, I have read some threads where it causes long starts.

My current problem is long starts and stalls.

90 renix 4.0 auto 207k

Clean the Throttle body and the Idle Air Controller and its housing.

CPS testing is below -


CPS Testing


Crankshaft Position Sensor Connector





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.

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.
*

Are you sure about that test procedure? I bought a CPS for my 1996 and I tested the old one and got an open reading across two of the terminals but when I tested the new one I got continuity and some resistance across any and every combination of terminals I could create. I'm not saying you are wrong I'm just wondering what happens if you get a pre 1991 CPS from the idiots at AutoZone.

ARBOGASTER said:

Are you sure about that test procedure? I bought a CPS for my 1996 and I tested the old one and got an open reading across two of the terminals but when I tested the new one I got continuity and some resistance across any and every combination of terminals I could create. I'm not saying you are wrong I'm just wondering what happens if you get a pre 1991 CPS from the idiots at AutoZone.

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CPS for 92-up HO models is entirely different from that in Renix. A good one reads open circuit. I think the 91 is unique. It sounds as if Autozone did give you the wrong one.

edit to add: yes, by the way, Tim's procedure above is correct.

I kinda figured he was right but I thought maybe somone could verify his method. It's hard enought chasing this misfire down without the parts guys giving me the wrong stuff.

How do you clean the throttle body? I did a search and about all I could find was use throttle body cleaner and spray it into the throttle body while the engine was running.

If you really want to clean it you will need some metric wrenches and some torx bits to totally remove everything. I scrubbed mine out with a toothbrush and some throttle body cleaner and then wiped it off and then used a 3M scotch brite pad (plastic pad not metal). Blow it all off with compressed air when you are done before you put the sensors back on it. It's pretty shiny now, inside and out.

you will have to remove it to do a good cleanup. With the proper tools(torx) you should have it back together in about a 1/2 hour. Be sure to scrub down the small spaces especially where the IAC goes

so I replaced the crank sensor. Starts but still shuts off. Also new tps and iac, plugs and oil, no wires yet.Cleaned grounds and changed some cables. so now whats good to check, fuel pressure????? seems fine since iI can accelerate but still not driveable.........

slowjeep said:

so I replaced the crank sensor. Starts but still shuts off. Also new tps and iac, plugs and oil, no wires yet.Cleaned grounds and changed some cables. so now whats good to check, fuel pressure????? seems fine since iI can accelerate but still not driveable.........

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I am having the same DAMN problem with my 97 gr. Cherokee but mine will run for 2-3 seconds then quit running. This is very frustrating when you keep replacing parts and have no success. Help.

Monitor your fuel pressure when this happens it should be around 50 PSI constant. After that monitor your spark and see how it is shutting the engine down. Check your cam position sensor in your distributor. I thought I remembered hearing something about if that sensor does not get a proper signal from some other sensors it shuts down in a couple of seconds. This also makes me wonder if you have a problem in your wiring harness with your CPS ? ? ? ? Just random food for thought there.

thats 50 psi for the grand cherokee right. what I am getting is a shutdown around a minute or two later.

If it is a 4.0 I would assume so yes. I believe spec is 49 psi +/- 5 psi

Check my thread about a new coil, I think the 4.0L 6 cyl mounts the coil like the 2.5L 4 cyl, on a bracket low on the side of the engine. It tough to see it clearly or fully where its mounted. When I pulled my coil, its case had numerous cracks in it and grime all over it, even though I tried to clean it several times. You really can't tell, unless you unbolt it and pull it out and look at it in good light.

A new coil solved a lot of the problems for me that people attribute to the CPS.

As well, Spark Plug Cables do wear out, they should be replaced every 60k miles, unless you have the new solid metal wire, coiled into a suppressive cable. At least check the resistance of the cables. Have someone start the motor in the dark, while you look at the motor, see sparks you know that is where your problem is. I have spotted a bad set of Spark Plug Cables once using this technique.

Thanks Rick I'll look into that!

tried checking all the cables, no luck, now I will lean towards the fuel pump and pressure regulator

yea i just posted a problem i wonder if my cps is bad.

My jeep in the am when cold fires up right away after 1 minute pull out onto the highway give her gas and dies to almost stall for 3 to 5 seconds then clears up and never does it again. it has started to have a higher idle then normal too.

Ive done new tps, map, 02, iac, iat, coil, cap, rotor, wires, e 3 plugs