Renix CPS wiring question

Just purchased a 1988 XJ 6cy and have been working to figure out a rough idle issue, feels almost like a slight misfire but have replaced cap rotor, plugs and wires. Was looking through the wiring last night and found two wires coming from the C101 that were cut and went to nothing. Started looking at my other 88 XJ to see what they went to and found that they used to go to the CPS but at some point a PO of my rig cut them and wired the CPS directly to the ECU (bypassing the C101. Does anyone see this as being an issue that could be causing my rough idle. Not sure if I should leave it or reconnect it so that it runs through the C101 again?

Moving it back will make matters worse.
That was a technical service bulletin repair from back in the day.

You are better off bypassing the C 101, Jeep actually made a kit to do that, had a TSB (technical service bulletin) about it. The shorter the wires the better, Just make sure the splices are good. I crimped mine, then soldered the crimp and covered with shrink tubing.

Check out Cruisers list, it could be anything from a CPS trying to fail, to a bad ground someplace.

I'd check for weak spark. Use an old plug gap it to 0.60 and hold the side of the plug against a good ground. Yellow large spark, a spark that splashes are weak. You can also hook up a timing light to each individual spark plug cable and watch the light flash on the relay block cover, misses show up quick this wy and you may be able to narrow it down to a single plug.

What kind of plugs you use and wires also has an impact.

The connection between the coil and the ignition module can get corroded, heat up and cause issues.

May be low voltage to the ignition module this circuit is kind of constipated and typically has around a volt of line loss.

May be dirty injectors. I periodically run a can of injector cleaner in with my fuel, seems to help some.

Vacuum leaks can also do this. Usually noticeable because you idle changes or cycles rhythmically. But can cause random misfires.

Getting a good idle on a Renix can be a head scratcher. Cruiser has just about nailed most of the possibilities in his check list.

Thanks for the quick response guys.

The plugs I put in are Champion Coppers and I gapped them to .35

New wires I put in were Bosch

Thanks for the input 8Mud.. I have a bunch of extra known good parts for a 1990 I parted out so in going to swap out the Coil and see what happens. Also I was spraying some starter fluid around the intake looking for leaks and the only leak I found that changed the idle was when I sprayed the EGR so I'm going to replace that to. Could air getting sucked in at the EGR cause a rough idle? Also it sounds like I have an exhaust leak but spraying the starter fluid around the intake gasket didn't do anything so can the gasket leaking around the exhaust ports only cause the idle issue also?

clean the ignition module,

replace the TPS ,

run 3 concentrated cans of injector cleaner through it

consider swapping injectors

check injector wiring

clean every electrical connection very well, everything under the hood

clean the grounds better than we did,


consider the c101 delete mod

If the EGR has some crap in the valve seat keeping it open it will definitely screw with your idle.

Plug off the vacuum hose for the EGR and see if it helps any. It should run just fine without an EGR, unless like I said the valve isn't closed all the way.
Different models of EGR, some you can see the rod between the valve and the diaphragm. You may be able to grab that rod with a pair of needle nosed pliers and twist it some and maybe work it up and down a little.

I've actually been able to get my finger tip on the diaphragm and work it up and down a little. Had one were the rod was jammed holding the valve open and moving the diaphragm a little unjammed it.

Like I said different manufacturers for the EGR some are partially open and you can see the rod some you can't.


Unable to think of anything better, I lubricated the rod and valve with graphite. Cooper high temp grease may have worked just as well.

Everything Blondejon recommended is relevant and something you are likely to need to do. It may not be one problem you have, but a collection of little things that add up. I eventually fixed my idle, but it was incremental, small improvements as I serviced corroded connectors and iffy grounds.

Finding a new gasket for the EGR may be impossible. Removing the bolts and you are likely to snap one off. I removed mine really gingerly, heat and lots of penetrating oil, more heat and more oil, wiggle a little and do it all again, then finally hold your breath and give them a good twist. I got my EGR piston to seat properly, blocked the vacuum line off and drove it that way until it was time for a new intake exhaust gasket and then fixed my EGR. A whole lot easier that way. If your diaphragm is deteriorated (leaking) the EGR is junk, mine was just jammed.

The vacuum solenoid for the EGR is a known trouble spot, the connectors get really crispy from old age and disintegrate. No power to the vacuum solenoid and it is open (normally open) and you have vacuum continuously to the EGR. When the EGR is open the motor idles bad and is likely to stall at low RPM's when this happens. The EGR is designed to only open at cruising speeds or simply put, RPM's higher than idle.

A couple more ideas:

Clean throttle body and new gasket. Espescially around the IAC hole and clean up that IAC with some alcohol, don't pull on on it.

Check your intake/exhaust bolts. Be careful of over torqueing that back bolt.

Generally, if there's an issue with the CPS, it's either going to be a no-start or it's not an issue. Bypassing the C101, and a lot of other things are sometimes required. Frankly anything dealing with the CPS, and that whole wiring harness (Mine's a 90) is my least favorite issue to have on the jeep.

Click on the link below and do Tips 1 through 5. consider doing #27.

http://www.naxja.org/forum/showthread.php?t=1115935