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CPS/CKP questions


NAXJA Forum User
Ok, so I've been having some starting issues, and after some searching here, it sounds like it is most likely thermal failure of the CPS/CKP. They symptoms are:

Cranks as normal, but will not start, usually only after towing something, or after bad traffic that would cause the temp in the engine bay to be higher than normal. After sitting between 10 minutes and an hour, it will fire right up like normal.

Now, assuming the CPS/CKP is the proper diagnosis, can someone point me towards some info on replacing it? I'm definitely no rocket scientist, but have proven to be a more than adequate part-swapper in the past. Has anyone done a write-up on replacement? Is the part I'm looking to replace the Camshaft Position Sensor, or Crank Position Sensor? Everywhere I've seen while searching it just refers to it as CPS or CPS/CKP. I've also seen some people note that it's a pain in the butt to replace. Can I get a little help here, or a point in the right direction? If there's a specific thread about it, I sure couldn't find it with my searches.

Thanks fellas, I know you all probably get tired of seeing this subject.

Edit: Forgot to mention it's a 97 4.0 with manual trans.
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You're best option if the Jeep is stock height will be to attack it from underneath. Looking at the front of the Jeep, the CPS (crankshaft positioning sensor) sensor is located on the top of the transmission bell housing, at the 1-2 o'clock position. It has two bolts that hold it in, I don't recall the size at the moment (something like 11 or 12mm stands out). It's a pretty straight forward swap, just in a tight spot. Extensions and universal joints are your friends on this one.

The Camshaft Positioning Sensor is located in the top of the distributor...but they usually don't give too many troubles.
the camshaft position sensor is the pickup assembly in the distributor if you have one. or in the shaft where the distributor would be if you have coil on plug.also a word of note. i had an 89 MJ that had some of the same symptoms as you. mine was a weak fuel pump. it would shut off. cool down and restart. have also seen these same symptons on the dodge minivans has been fuels pumps about 80% of the time. just something else to look at also.
To replace the CPS, I assemble about 2ft of socket wrench extensions with a wobble adapter on the end. Work from the transfer case area. Have a helper guide and hold the socket on the bolts from above in the engine compartment. Remove the upper bolt first and re-install the lower bolt first, you do not want to drop a bolt into the transmission bellhousing.

Some people remove the front drive shaft and reach straight up to the CPS.

The crankshaft position sensor is the most common "thermal failure" creating no-start conditions on the 4.0

The ignition coil though is another possibility.

Both of these parts can be tested for spec. resistance values. Testing them WHEN symptomatic though is recommended as testing them when the engine starts may be of no value.

Good luck and be sure to let us know what you find!
I would test first.

Tim_Mn has posted the test procedures many times, probably the best I have seen.

CPS/CKP both mean the same thing depending on the year of the FSM--crankshaft position sensor.

Synch sensor (stator) or CPS or CMP are referring the sensor in the distributor that provides input to the ECU/PCM so it can determine the correct firing duration of the fuel injectors.

As you can see, terminology has changed over the years, is different between manufacturers AND parts houses, and can be a little confusing.