Renix C101 Connector Refreshing


The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of more than 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.

That said, the cleaning described below is a real MUST DO right off the bat for any new-to-you Jeep. But, I strongly advocate eliminating the C101 at some point by following the procedure with photos and video in Tip 27. Soldering skills are required and it takes about an hour and a half.

The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the ¼” bolt and pull the halves apart. You will find the connector is packed with a black tar-like substance which has hardened over time.

C101 connectorTake a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.C101 connector

If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.

If you wish to eliminate this connector entirely (highly recommended), see Tip #27 – C101 Elimination

Revised 1-31-2016

39 thoughts on “Renix C101 Connector Refreshing”

  1. I have a 87 Pioneer 4.0 renix. So when I give it gas the engine seems to lag in & out of power. It “putters” then kicks into full power & she runs like new. But quickly returns to this putter. It happens in what ever gear its in. I’ve replaced the CPS, Plugs, Cap & Rotor, Fuses & Battery. I’ve cleaned the C101 connector. Cleaned & added ground wires. Replaced vac lines. I put fuel injection cleaner in with a full tank & it seemed to stop the putter until about a quarter tank. Recently it got worse so I revved to red line thinking maybe something is clogged & I’ll push it out.. It would stop the putter only Until next start up or red light or at random. That worked for about a week. Then I tryed turning on the front defrost when it puttered & that would make it stop for a little while but That does not work anymore either. I also recently unhooked the battery & did the Computer Relearn Procedure & it helped it tremendously…..but still does this Lagging/Putter. I even went to the junkyard & got a MAP sensor from an 88 but it made it worse so i switched back. I’ve searched the Internet for months replacing recommended parts & dumping money into the ol girl & nothin…..Please help

    1. The issue at 1/4 tank got my attention.

      Have you ever tested your fuel pressure? 31 at idle with the vacuum line connected to the fuel pressure regulator and 39 without it disconnected. The internal hose from the fuel pump to the outlet of the tank may be compromised, or the internal ground wire may be loose. .

      I might also try bypassing the fuel pump ballast resistor on the driver’s side inner fender.

      Look VERY closely at the line from the throttle body to MAP sensor.

  2. I found the fuel pump ballast located on my fire wall next to the c101. I was going to relocate it by the EGR valve. Also I see in the picture that there’s a single orange wire to each connector on the ballast….mine has 1 on one side & 2 on the other…I haven’t found info on that. When I got that map sensor from the Junk yard & plugged it in… made my jeep shake & vibrate when accelerating. Now the old map sensor does it too but didn’t before.

      1. Yes I still have the C101. Its still connected.
        I also found a disconnected wire but can’t find where it goes. The wire starts off from the “battery terminal” connection on the Starter relay. Its a green wire that quickly turns into 3 red wires. 2 of the wires go into the wiring loom & go through the grill around to the firewall. The 3rd wire isnt connected to anything But has a “connection” crimped on the end. The “Connection” is broken off but the Crimp is still on. The only info online I found on this is that it could possibly go to the latch relay. I can’t find where it would connect to on the latch relay though.

  3. First I would like to thank you for all of your very useful knowledge. I have a 1987 cherokee 4.0 auto. It was very abused when I got it and with your helpful tips it has come a long way. I have done many of your tips but have not eliminated the 101 yet. I just did the 1999-2004 wj brake booster upgrade. I had a terrible vacuum leak with the old one causing high idle at 1500rpm. Also I just installed a 1989 tcu which fixed the no downshift problem and has cleaner shifts between gears. The main frustrating problem I’m having now is it cuts out while driving. I drive 15 miles each way to work and it will cut out 2-3 times each way. Just driving along and loss of engine power, take foot off pedal, and usually regains power while coasting. If not one I pull over it will crank on immediately. Once it wouldn’t start at car wash and I found sparks popping out starter relay. I thought this may be it so replaced it. Still cuts out. I just replaced cps yesterday, but it did it twice in 2 miles this morning. I stopped to fuel up, 13 gallons, drove 1 mile home without issues. Sorry for long winded post, hoping you can help. Thanks, Flint Frame Boise Idaho

    1. First off, I’m glad to see the Tips have helped.
      Have you ever tested CPS output? Tip 7. Keep in mind it’s signal travels through that nasty C101 connector. Have you at least cleaned the C101 in the meantime?

  4. I have pulled c101 apart and cleaned. I haven’t checked the out put. Everything I read says if intermittent then won’t catch it with test. I am leaning towards coil, cap, cam sensor and wires next. Just noticed brake fluid in driveway. Looks like may be from new master cylinder. 1 step forward 2 back with this @$!#£?+₩ jeep!

    1. Well I fixed the cut out. I wanted to wait a few days and add some miles before making that statement. I pulled the coil and cleaned contacts and did the same with distributor cap. While there I realized I had never pulled the cam sensor connector apart for cleaning. I think this is where the problem was. It was wet with motor oil! When I got this jeep in October it was leaking oil pretty bad from the valve cover and ccv grommets. It had a combo of cork and rtv for a gasket. While I had it off I did the V.C. mod. New grommets and a blue felpro gasket rook care of the leak.
      I cleaned the oil out and have driven 100 trouble free miles. Now that’s fixed, my m.c. reservoir starts leaking! I had pulled the reservoir to clean it when I did the wj booster upgrade. That was 2 weeks ago, 300 miles without leaking. I’m guessing the grommets that mount it to m.c. are bad but the dealers can’t get me just the grommet. Reservoir from dealer was just under $200. And m.c. was close to $400. I’m headed back to junkyard for grommets and or another m.c. combo for $30.

  5. Other than the C101 connector, was there much difference between the engine wiring harness from 1987 to 1989-90? would a 1987 harness (TBI, from my understanding) work with the MPFI engine, with the extra wires for each injector added to the correct pin outs? the ECM seems to have been the same , so the plug should also be the same?

  6. Cruiser,
    If i had accidently applied +12vdc to pin d13, “ign interface out”,of my ecm (jumped the wrong yellow wire at ign coil to b+ while troubleshooting a no spark issue) would that have positively fried my ECM?
    89xj 4.0 aw4 BTW
    Thanks a million!

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  8. Hi cruiser54 i just bought a 88 xj and I’m having idle issues I’ve done everything to try and fix it. Is there anyway to post a video on here or can i send a video to you so maybe you can help me out.

  9. Hello Cruiser54,
    Let me just say Thank You. I have followed each one of your tips, and I am a happy boy. 1987 Jeep Cherokee 4.0l Pioneer. I do have a question that I am hoping you could help me with:
    I am converting to an all electric fans, and I am trying to find a switched 12v under the hood to wire into the new relay. Can you point me in the right direction? All of the other connections are there, and everything works. I just do not want to run a new wire all the way back to the fuse block. Any thoughts?

  10. hey cruiser ive read a thousand of your replies and ive done the tips on my 89cherokee but i cant figure out why it runs perfect when cold then as it warms up a hesitation starts and the hotter it gets the worse it gets im parts,ECU, fuel pump,fuel pressure reg,fuel filter,plugs,wires,cap,rotor,coil,comp cam,complete head service,timing chains,distributor,

    1. I wonder if the fuel pump is having issues and overheating.
      Try a new fuel pump relay and/or bypassing the fuel pump ballast resistor?

      Describe “hesitation”

      1. Hello cruiser, 88 Jeep Comanche a/t. Actually rained in California last night and went to star The Jeep up and it started and died. Now I have no crank. Cap and rotor replaced recently. I feel it’s tied to moisture but need help. Please advise! Thank you

  11. Hey Cruiser,

    Im trying to track down an issue with the coolant temp sensor. The one on the side of the engine block. I believe the sensor is bad or the path that goes back to the ECU is bad. Does the CTS go through the C101 connector or is a straight shot back to the ECU?

    Thank you

  12. I just purchased an 88 Wagoneer limited. It is all stock with a crank no spark condition. I want to get the C101 connector done first but found 2 wires in the loom that appear to be cut. 1 is purple/white the other is white/black, no other ends found. the cut ends go back to the male side of the connector. I cannot find anything on the wiring diagrams that show those color wires.

    1. I was incorrect on the wiring colors. Pur/white and yel/blk. The wiring diagram shows it to be the knock sensor circuit but its not shielded. I have not pulled the knock sensor yet to see if I have continuity. I dont that is the correct circuit anyway. The diagrams only show wiring out of the ECU and not out of the C101 connector

    2. It’s possible that a dealer performed the CPS bypass per the factory bulletin. Part of that procedure was to clip off the old wires. should have been taped back into the harness.

  13. Thanks for the write-ups!
    What about the connector to the back of the fuse block through the firewall?

    My wiggly fuses left me with a dead battery on the side of the highway…rather than get a little pick and bend them back like I now see you suggest, i removed the connector, removed the 2 large phillips screws holding on the fuse block, and managed to break at least one wire (vt/yel wire to blower from fuse). Now the engine runs super rich so either there’s a bad connection or broken wire? I ordered new spring crimp terminals for the fuses. Maybe time to order new crimp terms for the connector too?

    I also just had the fuel tank painted and pump reinstalled. fuel pressure is 31ish psi with reg connected through all rpm.

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