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verifying CPS AC test range? 89 Cherokee, 4.0 L

Old 02-10-2019, 06:47 PM
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Default verifying CPS AC test range? 89 Cherokee, 4.0 L

My 89 Jeep Cherokee Limited, 4x4 4.L is stalling out when idling after it runs pretty well for 15-30 min and then is parked (but still running).
After a min or three of "regular" idling in a reasonable range, it just has a slight cough, then dies without being touched. Last time it died I was verifying transmission fluid levels after driving 30 min, while hot, parked and running in idle.

Based on many other postings, I suspect the Crankshaft Positioning Sensor (CPS) could be one of the issues.

I tested the leads to the CPS with a multimeter per the Beeping Jeep guy YouTube video with the engine cold.

I'm getting 280 ohms on the resistance test (no cranking), and .4 volts maximum when set to AC volts while cranking the car (cold engine).

In his video he says the CPS should be spiking to .5 to 1 volt AC when cranking via the key. IF those numbers are right, my CPS is lower than expected.

Anybody able to confirm that?

I can also get it up to temp by driving it 30 min, then let it die in my garage and test it again, to see if the values are very different when hot. (I have NOT tested while hot yet.)

Just want to be sure I have the right numbers before replacing that sensor. While it's "only" 2 bolts, it sure seems like a tougher job to get to those bolts, that location with all the extensions and the limited access. (I'm not clear yet how people get the bolts started on the new one, but more videos to watch...)

I have done the ground refresh, and working through the Cruiser54 refresh steps (still a work in progress). Due to the refresh, basic tune-up steps and TPS replacement, Jeep is running 100% better than before, but still some nagging details. (Reverse gear not engaging correctly, documented in another thread, and this stalling out after running well for 15-30 min of driving.)

When I get these two issues resolved, I may have an around town drivable Jeep.

All input welcomed.

Last edited by Unlikely; 02-10-2019 at 06:58 PM. Reason: clarifying details
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Old 02-11-2019, 07:10 AM
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Mod the CPS you have?
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Old 02-11-2019, 07:16 AM
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No mods at all.

Simply using a multimeter to read the values of the pins from the CPS before considering replacing.

Just want to verify the values I'm reading are valid, or outside the range of what is expected BEFORE throwing parts (new CPS) at it.

If there is a better method for testing, I'm all in... If there are other items related to stalling out, I'll verify those too once I know the best practices...

Last edited by Unlikely; 02-11-2019 at 07:18 AM.
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Old 02-11-2019, 07:44 AM
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What's your AC voltage reading?

There's a mod you can do that increases your CPS output.
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Old 02-11-2019, 01:12 PM
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Originally Posted by cruiser54 View Post
What's your AC voltage reading?
<snip>
AC voltages: Totally cold engine (sitting overnight).
It "cycles" a minor range between 3/10 and 4/10 of a volt.
Here's the cycle I'm seeing:
.32x
.38x
.42x.

It starts at .32x then it maxes out at .42 volts, it cycles back to .3x again...
I can video that if it's helpful to see the exact sequence I'm reading.

Happy to mod if that's something you recommend. Right now it's hard starting, takes usually cranking it once for 10-15 seconds, a pause, then cranking again and it tends to start after 5-10 seconds the second or third crank.

Then it will run for 15-30 minutes while driving, and runs and feels "normal".
Very limited experience with "normal", since I only have my limited "test drives", all 5 to 30 minutes max, less than a dozen "drives" so far, mostly residential streets as I'm verifying the fixes.

IF I turn it off in the first couple minutes, it starts right up immediately, on the first crank, within seconds, like a normal car starts.

AFTER driving for 15-30 minutes and fully up to temp, it will stall when idling, OR if I turn it off, it then won't start up immediately in the first 10 min or so. It simply cranks via the starter. I have to wait for it to cool down a bit (10 min or so, didn't really time it...), then it will start up, often after some cranking.

After sitting a few hours (or overnight), it is back to the original symptom "crank twice or three times, then starts and runs "fine" while driving until you idle, then it turns off at some point, and hard cranks again...

In the videos I watched, they implied the CPS should be outputting half to one volt when cranking, but I wanted to verify that is valid BEFORE purchasing/changing a new CPS.

I appreciate all feedback.

Last edited by Unlikely; 02-11-2019 at 01:14 PM.
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Old 02-11-2019, 06:09 PM
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You are correct in the voltage testing/values.

Have you completed tips 1,3,4, and 5 yet?
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Old 02-11-2019, 10:07 PM
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Originally Posted by cruiser54 View Post
You are correct in the voltage testing/values.

Have you completed tips 1,3,4, and 5 yet?
I have almost all of those tips finished, but I'm going to double-check them all and will report back after (will may take me a day or two, since I don't get to work on this stuff every day...)

I'm not clear on "... correct voltage" comment above.

That means my sensor is returning what you would expect?
Or it's out of range and might need replacing (assuming all tips are finished/verified).

This page at the bottom implies the sensor should be reading a higher AC voltage when cranking, but I'm still figuring this all out and may have it confused:
https://www.cherokeeforum.com/f51/testing-cps-5563/

All input welcomed.
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Old 02-12-2019, 07:05 AM
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Your CPS could be modified to put out more voltage and it is suggested you do so.

It wouldn't hurt to test it's voltage at the ECU also.

Is this vehicle manual or auto trans?

tip 5 is important to jump to soon.
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Old 02-13-2019, 11:23 PM
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I'm happy to say 1, 3, 4 & 5 are done, with 2 exceptions for #3 (unplugging/cleaning/replugging ALL electrical connectors in engine bay.)

That 10 pin connector in the front left you mention in tip 3: I can't get that one open yet. I messed with it for an unreasonable amount of time, and decided to cycle back on it.
I can't get two hands down there yet, but I will refresh it next time I take out the air box again. (I took the air box out to do the power steering hoses, but didn't think to deal with the plug then... Not smart.) If someone has good tips for pulling that apart in the existing restricted space, I'm all ears.

I did NOT disconnect all the fuel injector connections.

Other than those exceptions, all connectors, relays, and the coil were opened, cleaned, put back together. All spark plug wires and distributor/rotor replaced. (Spark plugs replaced about a month ago...)

On #5: My ohm meter is reading .3 ohms or less in all test cases I tried.

I also found a ground on the drivers side that had two wires bolted to it. I had never seen that one before, but I unbolted it, cleaned the wires, wire brushed the bolt/part of the car, Ox-garded them and put them back together. Not sure if it made any diff, but can't hurt having more grounds...

*******
BTW - On first test drive after all steps completed, it ran rougher than I remembered and seemed to have less power. I'm suspecting I didn't get a plug wire seated right, I'm going to cycle back and redo all those over the next day or so.

*******
Now I'll see if I can find the tip on increasing voltage from the CPS... Not sure how to do that mod yet. Seems like that's worth doing before replacing the CPS. (If I'm missing something, please advise!)

Found one vacuum hose that went to a valve in the cooling hose, that I couldn't find where the other end of the hose belonged. I'll post that in another thread with a photo. Someone hacked my cooling system with a mod that I don't understand, but you have to see this to believe it...

Last edited by Unlikely; 02-14-2019 at 01:39 AM. Reason: clarification
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Old Yesterday, 01:37 PM
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OK, I finally got that 10 pin connector open (Drivers side, in front of the air box, behind the headlight).

Took me far longer than I'd hoped, but it's done. That was the most corroded connector in the vehicle, by far.
A little flat head screwdriver on one side, got it just open enough to pull out that side barely beyond the clip, then worked the other side. Took a while as working on the second side was re-clipping the first side, but figured it out.

I have no idea what it handles, but now it's back together, corrosion removed. (Wire brush on male pins, plus contact cleaner. Contact cleaner and pipe cleaners on the females side...)

I'm thinking of leaving the fuel injectors plugs alone for now. (If I get the Jeep working reasonably well, I'll upgrade the injectors too, but working to make sure the basics are solid first.)

If others are doing this, it's worth the effort to get that plug refreshed. Not simple for me, but yours may be far easier.

Now I'm confident all steps for refresh through #5 are done. I've measured ground for #6 (Sensor ground splice removal), and so far mine seems solid, I have NOT removed those splices at this minute. After my other ground refreshes, this seems solid on this vehicle so far... Open to all input on next steps.


Hard to see, but more corrosion on this 10 pin than all the other connectors in my Jeep.

Photo doesn't show all the green corrosion inside those holes, but more than expected. Worth the effort to get it apart and cleaned.

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