Something to Consider When Testing Your CPS

Today I happened to have the engine running in my '88, insuring that it would run after I re-did some of the wiring. I had in my hand the CPS connector and was trying to figure out how to best tie it up and out of the way when the engine died. Long story short, after several restarts and further fiddling with the connector I figured out I had a bad connection between a pin and a socket. As near as I can figure I distorted or otherwise compromised the connection by jamming the probe of my meter into the CPS side connector while diagnosing a crank/no start condition. I replaced the mating pair with a Deutsch-tech set I had on hand and all is well. I doubt this was the source of all my problems I'd been having. Those seem to have gone away when I had all the fusible links apart and cleaned their connections...I've since replaced them all. But this is something to keep in mind when testing your CPS...You can actually create a poor connection by stabbing the pins with your meter. Who knew??

Yeah I've bent the pins and fought with mine before. I thought the same but proved myself wrong.
Normally that's not the issue and each time I've thought this fixed by bad pins. it failed again within a week stranding me.
I think unplugging them and replugging/jostling the wires somehow gives them a tad more life. (I suspect due to cheap construction.)

Many of the pins in the connectors are prone to oxidation. Where the wire is crimped, in many instance, it is prone to oxidation on the wire. on the crimp connector and between the wire and the crimped connector. I've even found broken wire (fatigued) under the insulation, the only good conductivity was when the wire under the insulation was in a certain position and made touch contact. I've even found oxidized solder that was mostly dust (oxidized lead and tin).

Point is a lot can go wrong with the Renix wiring. My solution was to eliminate as many connectors as practical, then solder and shrink tubing. Seal the ends of the shrink tubing with a drop of super glue. Over the years piece by piece I worked the bugs out of my harnesses and my Renix ran, idled and performed better after 20 years than it did new.

Rumor has it that the harnesses were made in Mexico way back when and quality control was poor.

One overlooked thing I found was the pins in the ECU connectors were prone to back out of the holder or where never pushed all the way in. The contact surface was really reduced and likely caused some resistance. A little resitance here and a little there all adds up.

A side note that may give a little insight was my TPS ground, transmission side and the ground, engine side, of the TPS were swapped. I found a crimp connecotor that was never crimped etc. for my TPS ground, I spent many hours with a quality ohm meter working the bugs out of my harnesses.

blu3fan said:

Yeah I've bent the pins and fought with mine before. I thought the same but proved myself wrong.
Normally that's not the issue and each time I've thought this fixed by bad pins. it failed again within a week stranding me.
I think unplugging them and replugging/jostling the wires somehow gives them a tad more life. (I suspect due to cheap construction.)

Click to expand...

Twenty years ago when I first got this Jeep I had a lot of problems with it dying on me. The test then, as now, was to disconnect and reconnect the CPS. If it worked, that was your confirmation that the CPS was at fault. It would work for a little while, then start happening again. I eventually found a post about a factory 'kit' that included a new CPS and a small harness that bypassed the factory harness-including the C101 connector I have on my '88), all for less than the cost of a CPS by itself. The parts guys at my local dealership didn't even know about this when I had purchased the CPS by itself before. I walked in with the part number on the kit to find they had it in stock the whole time. This fixed the problem for a LONG time...until late last summer. At the time I went straight to the CPS because of my memories of twenty years ago...I figured the CPS was on it's way out after the 150k miles I put on it since it was replaced. I replaced it and, it made no difference. It would still die on me on occasion. Worst still, it got to a point where it didn't want to restart very easily, leaving me stuck for as much as ten minutes on the side of the road...cranking, waiting, cranking, waiting (to avoid overheating the starter), cranking, waiting...fiddling with connectors and what not under the under the hood as well. Last September I just parked it...kinda hoping it would just 'disappear' or something I guess. fast forward to several weeks ago and another project that had been a priority for me stalled due to waiting on some parts & tooling, I decided to have a look at the Jeep. The first time I tried to start it it fired up and ran great. A week later, nothing. It cranked over, but wouldn't fire. By accident I got it going after removing, cleaning and reassembling the fusible links ganged up on the starter relay. At least I think that's what did it. It starts and runs fine now. I haven't braved actually driving it further than around the block yet.



By the way...there are two large flat Delco style weatherpack connectors by the battery/relay area of the engine bay. Does anyone know what circuits they go to? I'm thinking of replacing those as well. Or at least pulling the pins and sockets and cleaning them...maybe give them a light squeeze with some pliers to restore tension to them.