Fouling CPS - thoughts?
 

So I've had a very strange condition.

I drove to a store, went in for 10 minutes, came out and my jeep would crank and wouldn't start, had it towed home and it was the CPS. So I replaced it.

Drove it to work Monday, worked for 8 hours, came out and same issue.

I replaced it with an OEM unit from jeep, that was the prevailing wisdom was that it was a cheap aftermarket unit that failed.

The jeep is getting towed home today and I'm pretty well sure that it's the CPS again, I'll know when I pull it off and can confirm it.

Is there anywhere to start that may be causing the CPS to fail? Where should I look? A short? a ground? ETC.

The rest of the ignition is new (within last 6 months) - coil, pick up, plugs, wires, rotor, etc. I have the 5-90 wiring upgrade and an optima yellow top.

How did you determine it was the CPS the first time you changed it?

Was getting no spark, so I swapped coil, swapped pick up, still no spark. Went to the CPS, pulled it - absolutely no magnetism. So I replaced it with the OEM Jeep one and it fired right up.

Does "the key trick" work? (95 might have been the last year)...

1) Start engine (if possible). Move transmission shift lever
through all positions, ending in Park. Turn A/C switch on and then off
(if equipped).
2) Turn engine off. Without starting engine again, turn
ignition on, off, on, off and on within 5 seconds. Record 2-digit
fault codes as displayed by flashing MIL.
3) For example, fault code 23 is displayed as flash, flash,
4-second pause, flash, flash, flash. After a slightly longer pause,
other codes stored are displayed in numerical order. When MIL begins
to flash fault codes, it cannot be stopped. Start over if count is
lost. Code 55 indicates end of fault code display.



The code key is in info threads top of the forum.

Hm, I've never heard of that.

OBD. On board diagnostics. 95 is OBDI, 97 is OBDII. Not sure about 96, and later it doesn't work, or maybe just for dash issues? Idk. Does show stored codes 91 to 95....

96 is OBDII....

If you are having repeated CPS issues you should examine the wiring going to the CPS connector for chafing/broken wires. And check the CPS engine harness connector for corrosion.


And, check the wire harness loom coming out of the fuel injector manifold for chafing at the end of the fuel rail.

^^ This.

And you should check the computer for any codes or pending codes. Easy to do on a 96 with any code reader or scan tool plugged into the port under the steering wheel.

The odds of you having 3 crankshaft position sensor failures is extremely low.

What do you mean when you said you tested the crank sensor and it had absolutely no magnetism??

Checked yesterday, didn't see anything glaring. I need to get it towed to my house so I can really see what's going on.

Don't see a pending code actually. I thought that as well with the CPS failing a 3rd time.

On the CPS, the end that goes into the trans is magnetized, that's how it picks up the signal. At least from my understanding, I could be wrong though.

Could you tell me what the wire colors are going to the CPS connector?


Look in the CPS connector. Are there flat pins or round pins in the connector?


What month/year was your XJ built?