Crank Position Sensor repeatedly fails - JeepForum.com
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post #1 of 12 Old 11-17-2017, 11:09 PM Thread Starter
JeepNovice63
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Angry Crank Position Sensor repeatedly fails

I've seen plenty of threads where diagnosing a bad crank position sensor is the topic. I've got the diagnostic part down cold. The CPS on my 2000 XJ 4.0 automatic has gone bad FOUR TIMES in ONE YEAR. That's no typo. FOUR TIMES. It's starting to drive me nuts. Not just because it's such a pleasure to replace, but WHY???!!! The last one to go bad was purchased directly from MOPAR. What would make this sensor repeatedly fail? Bad ECM? It's not the wiring getting burned on the block. The sensor is going bad. Anyone ever seen this before? Any help you can give is VERY MUCH appreciated.
Sincerely,
HatingMyCPS

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post #2 of 12 Old 11-17-2017, 11:28 PM Thread Starter
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Will replies trigger an email to me?
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post #3 of 12 Old 11-18-2017, 06:22 AM
tjwalker
It's the crank sensor!
 
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When you pull off a suspected fail sensor, does it actually test bad with a meter? Compared to testing of a new sensor?

If you haven't already done that, I would and here is why. It is possible that you have a problem with the crank sensor "circuit" and that replacing the sensor allows the circuit to work for a while until it fails again down the line.

By "circuit", that means all wiring and I would be especially suspect of the CONNECTOR.

If the sensors are truly prematurely failing, you mention that the last one was an OEM. So it is theoretically possible that the first 3 aftermarket sensors you used were of poor quality (not at all unusual with this sensor) and didn't last and that the last Mopar crank sensor that failed was just pure bad luck for you.

Good luck, stick with pure Mopar crank sensors and keep us posted!
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Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #4 of 12 Old 11-18-2017, 07:12 AM Thread Starter
JeepNovice63
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Thanks for the reply. Each failed sensor has throw a code on the scanner. The code disappears after the new sensor is installed. Sounds like you may be suggesting testing the old sensor after itís removed, which I didnít even know you could do. (How?) Your thought about the circuit, and specifically the connector makes a lot of sense. It LOOKS ok but who knows? Seems unlikely that 4 sensors in a row would go bad that quickly. Next time it goes bad, which may be tomorrow, I will focus more on wiring and connector. I am considering, regrettably, cutting a quick access door in transmission tunnel. Any thoughts on that?
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post #5 of 12 Old 11-18-2017, 08:15 AM
jtec
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I wonder if you are replacing the component solely on there being a code, ie p0320 and replacing CKP?

some thoughts

What is the code ?
Any other codes?
You are using scanner ?
What is in freeze frame ?


following on tjwalkers idea - engine running - shake wiggle tug the harness to CKP, see if sensor signal drops. Maybe recreate freeze frame conditions,
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post #6 of 12 Old 11-18-2017, 08:20 AM
tjwalker
It's the crank sensor!
 
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I agree with jtec, post the EXACT code that you are seeing.

There are some OBDII codes that can trigger for either the cam sensor OR the crank sensor.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #7 of 12 Old 11-18-2017, 12:37 PM Thread Starter
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Well, like a moron, after I installed the new sensor I cleared all the codes. What I do know is this: before= cranking and cranking and no start. After = immediately started. Initially thought it was fuel pump, but pressure was ok. Plugged in the Actron and it threw a code (which I canít remember). Wrestled and contorted a new sensor into place and it started right up. The new one is from Napa. Last one was direct from Mopar. It lasted 3 months.
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post #8 of 12 Old 11-18-2017, 04:09 PM Thread Starter
JeepNovice63
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Looking through the replies above I believe it was 0320 code. Not certain, but it rings a bell. I think I will try the wiggle test now that itís running and not throwing codes
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post #9 of 12 Old 11-19-2017, 08:00 AM
rlitman
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Is this vehicle distributor less? Have you checked the sensor signal with an oscilloscope? That is the only sure way to know that the sensor is good or bad.

Oh, and does your sensor use one bolt or two? That can affect the installation procedure.

Iíve had issues with a 1 bolt sensor getting good signal using the original paper spacer. I respaced it with two layers of blue painters tape, which got it closer, and improved the signal quality.
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post #10 of 12 Old 11-20-2017, 04:21 PM
2oldjeeps
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scope pix i took.
oops? cant upload

tried to attach, no luck. pix is 5 v pulses.
ill work on it
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post #11 of 12 Old 11-20-2017, 04:28 PM
2oldjeeps
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3rd try.
scope on signal wire from cps
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a cps 1.jpg  
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post #12 of 12 Old 11-20-2017, 04:34 PM
2oldjeeps
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cam signal

same scope, 5 v pp signals

i dug into the cable bundle on the driver fender to find the right wires, color code from haynes. too hard to get at sensors direct.
i hope to get back to this with a synced dual trace scope soon..
get both signals on one screen.
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aa cam sensor.jpg  
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