New, Defective CPS?

I think I got one.

I bought a Well's brand CPS about 2 weeks ago and replaced (before I caught the buy Mopar mention). Car ran great for about two weeks. 3 days ago, I had a hard time starting it (about a dozen cranks). Then 4-5 good starts over the next few days. Last night it started up after 2 cranks, went to the gas station and it did it again! I did the unplug plug back in of the sensor and it started right up.

Did I get a shitty one?

Nevada City Sparky said:

I think I got one.

I bought a Well's brand CPS about 2 weeks ago and replaced (before I caught the buy Mopar mention). Car ran great for about two weeks. 3 days ago, I had a hard time starting it (about a dozen cranks). Then 4-5 good starts over the next few days. Last night it started up after 2 cranks, went to the gas station and it did it again! I did the unplug plug back in of the sensor and it started right up.

Did I get a shitty one?

Click to expand...

Bad contact in the plug? Are the symptoms the same as you had with the OLD cps?
If so I doubt you have a bad CPS.

Yeah, it's probably high resistance in the plug. There's products out there that enhance conductivity: Oxi-guard, Kopr-Shield, to name two. You could try some of that on the plug connectors, and see what that does. You have to use it sparingly to prevent causing a short; I apply it with a toothpick.

It's found in electrical supply stores. Eastwood Co carries the Kopr-Shield.

I just replaced a CPS, that tested good with and ohm test, but replaced it anyway. It´s been working well since.
But if it does act up again, I´m going to wire (solder) the CPS leads straight to the CPS wires going through the firewall as close as practical. To bypass as many connectors (and bends) as possible. Eagle says there is a kit from Jeep to do this, that doesn´t require cutting and soldering.
Where the injector (CPS and other sensors also) harness bends at the firewall, is a trouble spot. I found the wire fatigued through, under the insulation right at the bend on my old 87. I guess from the motor rocking and working the wiring at this location. Finding a break or partial break under the insulation can be interesting.
The long lead from the CPS to the plug, is known for cooking on the exhaust header. I re-routed mine and tied it lossely to the speedo cable, well away from the exhaust manifold.
Old Man recommended that if mine acted up again, to check the flex plate for cracks. Which I did anyway, pretty easy to take the inspection cover of and look at the back of the flex plate for cracks. He also said if it acts up some more, to check the clearance between the pickup and the (tone?) ring on the flex plate. Which seems almost impossible without pulling the motor. Not much room to work in there.

8Mud said:

I just replaced a CPS, that tested good with and ohm test, but replaced it anyway. It´s been working well since.
But if it does act up again, I´m going to wire (solder) the CPS leads straight to the CPS wires going through the firewall as close as practical. To bypass as many connectors (and bends) as possible. Eagle says there is a kit from Jeep to do this, that doesn´t require cutting and soldering.
Where the injector (CPS and other sensors also) harness bends at the firewall, is a trouble spot. I found the wire fatigued through, under the insulation right at the bend on my old 87. I guess from the motor rocking and working the wiring at this location. Finding a break or partial break under the insulation can be interesting.
The long lead from the CPS to the plug, is known for cooking on the exhaust header. I re-routed mine and tied it lossely to the speedo cable, well away from the exhaust manifold.
Old Man recommended that if mine acted up again, to check the flex plate for cracks. Which I did anyway, pretty easy to take the inspection cover of and look at the back of the flex plate for cracks. He also said if it acts up some more, to check the clearance between the pickup and the (tone?) ring on the flex plate. Which seems almost impossible without pulling the motor. Not much room to work in there.

Click to expand...

You can some times find a broken wire by pulling hard on a section of wire, you can feel it give a little, or it won't feel as solid as one thats not broken(kinda
Stretchy )


). Don't pull on the connection where the wires go into the CPS. You can pull quite hard though on the rest, 20# or so.

OK, I'll try the connection goop and check the wires. It does look a bit worn by the firewall at the bend. That could be it.

It'd really piss me off if I had to swap again. Although this time I shouldn't make every mistake in the book and should be able to avoid dropping the screws into the tranny again.