Trying to test CPS

[JeepsOLot]

Here is what Cruiser has in his tips:

 

Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected. You should get a reading of .5 AC volts. If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.

 

What I don't get is how can you test for voltage with the CPS disconnected? I'm definitely missing something here, but, I don't know what it is. I put the leads on both terminals of the disconnected CPS, both new and old, and I get nothing using A/C on the voltmeter.

 

Jerry

[JeepsOLot]

Forgot to add, I tested while trying to crank.

 

Jerry

[Eagle]

What happens is that the CPS has a magnet in it. The flywheel (or flex plate, for an automatic) has unevenly-spaced bumps around the perimeter. When one of the bumps interrupts the magnetic field, it generates a small electrical pulse -- essentially like a generator. If the pulse isn't strong enough (approx. .5 volts), the signal won't be read by the ECU.

[JeepsOLot]

That's what I figure, but, I'm not getting any volts from either the old or new CPS's. Want to make sure that 1. I'm testing them right, and 2. that I didn't get a bad new CPS.

 

Jerry

[Eagle]

Well, that IS the test for the CPS so, either your new CPS is defective or you're not running the test correctly.

 

You are using a digital multimeter, yes? And the dial is set for A/C volts? You are probing the connector to the CPS, not the mating connector to the vehicle wiring harness?

 

IMHO the resistance test is useless. The FSM says to measure the resistance, but they want us to measure it at normal operating temperature. How you're supposed to get an engine that won't start up to normal operating temperature is a mystery to me.

[JeepsOLot]

LOL, yeah, no kidding! Well, something happened to the new CPS, as after getting it out to take it back, this is what I had:

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I have no idea what happened, but, it wasn't good!! I just got another one, and it seems to be working. Now, I'll just have to clean the injectors, hopefully, it will run more then two seconds! Thanks, everyone!

 

Jerry

[onlyinajeep726]

Well something ate that one lol.

[Eagle]

Do the two bolts that hold the CPS into the bell housing have shoulders that fit tightly into the holes on the CPS mounting ears? Those are supposed to be shoulder bolts, and the shoulders are necessary to locate the CPS fairly precisely. The tip has to clear the bumps on the flywheel while being close enough to generate the electrical impulse. If a previous owner lost the shoulder bolts and used regular bolts with full-length treads, you could have mounted the first CPS too close, and it got whacked the first time you turned the enngine over.

[JeepsOLot]

Well, seems like it's working now, don't want to take them out again. I used a 7/16 socket to get them out, and, yes, it has a shoulder on it.

 

Jerry