CPS testing
 

I was checking out the 'how to' forum and was reading the thread about how to test the CPS. It indicates that on later model Jeeps (as in my '97) there should be no resistance between pin B and C. So that's the only test? And if there's no resistance then my CPS is good? There's got to be more to it than that.

I did a little google about this and some other manufacutres say that while cranking there should be AC voltage, is that the same case for our CPS? If so, how much voltage would indicate a good or bad CPS?

For the older XJ (87-90) you test for AC voltage but those are a completely different design.

For newer ones, yes.....it's a simple resistance measurement.

But testing of crank sensors is "not" always conclusive................so keep that in mind.

If you buy one, do yourself a favor and buy it directly from your local Jeep dealer. Aftermarket crank sensor are "hit and miss" with a lot of miss.

My local jeep dealership is a thief. Last time I walked in there to buy an oil pressure sender they quoted me over $100. I can only imagine how much they'd want for a CPS.

A resistance test, as described in the how to section, tells me nothing. Reading no resistance doesn't in any way indicate a working part, but merely a charateristic of a working part.

I'll do some price checks and report back tomorrow. I am however, not interested in buying parts I don't need.

Advance Auto and Autozone both want $76.

I paid about $55 or so abouts a genuine MOPAR crank sensor online. Here.

https://www.moparonlineparts.com/

Some back story as to why I'm asking about my CPS and how to test it. Took my XJ out for a short drive on Saturday, drove about 15 miles. About two blocks from my house a person in front of me made a short stop which required me to hit the breaks hard. As I did the Jeep stalled (may be because I dont' have a vacume ball yet- opinions?). Anyway, I started the jeep back up and drove to the next intersection and it stalled again, only this time it wouldn't restart. Checked fuel at the schrader valve, looked okay. grabbed an old spark plug I keep in the jeep and plugged it in to check spark- had none. My brother came by with his TJ and towed me over to my house.

I tried to start it a couple more times that day with no success. Next day I movtivated myself to try to figure this out. I suspected it was the CPS as it is orginal (as far as I know) with a couple hundred thousand miles on it. But when I "tested" it using the proceedure in the How To section of this forum it "checked ok". I use quotes there because that test really isn't a test IMO.

So I plugged the sensor back in and tried to start it a few more times- nothing. Left it sit for a couple more hours and decided to check voltage to the coil (since my CPS must be okay?). First thing I did was pull the front two 40amp maxi-fuses in the underhood fuse box. They were not blown but there appeared to be a small amount of corrosion on the blades. I cleaned them up with sand paper, plugged them back in and it started right up. Could my problem really just have been dirty fuses?

Hey there Cherockee...sounds like you got it, one way or the other. I couldn't answer you myself without spending some time with an accurate diagram. I might double check...make sure I didn't bump something else in the area while I was cleaning that up. (just to help be sure is doesn't do it again on the freeway, or in a rain storm!)

Anyway I did get this on the later cps. Yea, the voltage test is quick & simple for renix, but I guess there is a process for an AC test on the later as well. Looks like he may be seeing .35? Anyway sounds like you got it;;;;;

On YOUR CPS, I recently found this link on testing the later, OBD II CPS, which may well apply to yours. I haven't tried it, don't know anyone who has. It looks like he's verifying XXXa volt, (XXXXXXXXX Mil.Volts), presumably AC, (with a true RMS meter), (back-probing, with it connected), at his third (Red) wire. (not the ground, and not the 5V-DC sensor feed). I don't know what % difference I would expect from my "cheap-o-meter", as opposed to the true RMS, but it might not be much. (about 7 minutes into the first Vid, IIRC) http://www.cherokeetech.com/VBull/sh...agnosis-Videos

Awsome, our Renix expert comes through. That's how you test something. Funny thing is, about 30 seconds into the video I remembered I've seen this before, lol. Been so long I completely forgot it or where to find it. A mod should contact the video owner and ask to have it posted in our HOW TO forum. Very helpful. Thank you so much.

Ha! Well thanks...I can "parrot" Cruser sometimes..not to forget others..I think it waz Lareto, (not 5-90) that provided the obd,- cps clip. Maybe partly for the same reason I did. No idea if it works. The guy on the clip seems pretty competent, but someday, someone with a post renix cps might verify what's there for CF.

edit..http://www.cherokeetech.com/VBull/sh...agnosis-Videos

OK, I just watched it the um-pethenth time. Gotta look again, he says something around 2:minutes about his connections. I think he means he has his meter ground grounded, (and the middle wire is ground), and the outers, end up transferring the signal, a red being the one the PCM might be watching. (not the shared 5v sensor feed).
http://www.cherokeetech.com/VBull/sh...agnosis-Videos ..

So..., what do you get if you back-probe, (tap to), the sensor wire with a regular "cheap-ometer". Rrich might "chime in" that that will "instantly destroy" it. Feeling brave? Maybe some bold soul could step forward, and tap that. Not the grounded one, not the 5 V feed when it's turned on, but what might be the red one. He was cranking at .35 acv (,<edit), with a meter that is no longer available, but the ones like it are way spendy.