Renix ECU Connector Refreshing

Renix ECU Mounting

Many times, when other fixes have failed, it becomes necessary to eliminate the ECU to harness connections as a cause. This requires removing the ECU. Up under the dash, to the right of the steering column is the ECU mounted to a black bracket. The bracket is held in place by two 10mm nuts to the underside of the dash. It’s most easily removed using a ratcheting wrench but a socket will work.

Once you get the ECU down, unplug the two harness connectors from it. Visually inspect the connectors and pins.

Using a good quality electronics cleaner, liberally spray both of the harness ends and the ECU pin area.

Now, take a small pick or a dental tool and go to the harness connectors. Using the tool, tweak each female receptacle in the harness plugs so they will grasp the ECU pins more tightly.

Plug the harnesses back on to the ECU and reinstall it.

Revised 1-31-2016

40 thoughts on “Renix ECU Connector Refreshing”

  1. Does the Renix ECU need to have the Learned Memory cleared after any repairs as the later Jeep PCMs ?

  2. On the one harness coming into the ECU I have a bare, uninsulated wire that doesn’t seem to be connected to anything. Is this a ground, and if so where should I connect it? Btw… thanks for all of these tips!

  3. So I have a really weird issue if I plug the ecu in and keep the wires straight it won’t start but if I bend the wires making a right angle it fires and stalls but if I twist the computer two times and fold the wires over it fires and idles fine but as soon as u set the ecu Down it stalls

  4. Hey cruiser, did you ever came across a pink color coded ecu? Reference S 101144202 A -53005624. European market model, ‘90 model year. I’m chasing my tail trying to get in closed loop but everything i try seems to have the same outcome: crashing into a brickwall. Good grounds everywhere, bosch and ntk sensors tested, absolutely zero air leaks on intake and exhaust, 2 map sensors, new coolant and intake temp sensors… this XJ never had an o2 sensor until i got my hands on it, only a M18 bolt in place of the sensor and it does not look like a hack its hollow on the inside, factory built without cat (because euro regulations). Burns fine but maybe a little bit on the lean side, runs pretty much fine, etc. I’m finally thinking… maybe this ecu does not have closed loop because it never had a catalyst in mind?

    1. What tester are you using?
      Can you see what the O2 sensor is doing?
      It should go from .1 to 4.9 volts quite rapidly or “rich/lean, rich/lean” very fast.

  5. I pulled the ECU and now trying to figure out how to disconnect the harness from it without damaging anything.

    Is there a special technique to removing the harness plugs? Or is it a simple matter of just grabbing them and giving a good yank?

    Much appreciation.

  6. Would replacing the ecu with a later model version be an acceptable reason to get a little more power? I have heard it gives a little more power. Is this a reasonable upgrade?

  7. On my 1990 renix 4.0 I am trouble shooting the ecu stuff.

    On the egr solenoid valve which is located next to the fuel pump ballast resistor I get the following…

    with ignition on I get 3.75 volt across the connector (between the orange/black wire and green/ white wire) this measured with connector removed from the solenoid valve.

    I however get 14 volts measured Orange / black wire to chassis ground point.

    My understanding is the solenoid should always have positive battery voltage on the Orange / black wire when ignition is on, and that the green / black wire is a switched ground via the e.c.u. I ohmed the green / black wire to chassis ground and get 45 ohms, thus not a very good ground.

    where should I look for the poor ground? The manual is not clear as to the wire routing now what connector or splices there maybe in the path to ground.
    I am losing near 10 volts someplace. the 3.75 volts is not enough to trigger the egr solenoid



  8. also on the ecu (1990 4.0 liter) is the C4 connector the ground source that the ecu uses to send ground to the egr solenoid? and what is C3 with the 14 gauge green wire doing, it appears to be a positive from the battery via a couple connectors.

          1. Not really. There is an ohms test somewhere, but it would pass faulty sensors. Whatever you do, do the cPS mod in the write-up.

          2. Ended up being a faulty TPS. Reading 89% – WOT. Hence shut down power to injector. Thanks for the help.

          3. The CPS generates its own voltage directly to the ECU.
            Are you saying that the TPS was reading full throttle? coulda been. That would tell the ECU to “clear flood” and send no signal to fire the injectors.

  9. Precisely. I only knew this because of the expensive computer I plugged into it, drawing data from the engine.

      1. My friend insisted on trying his Apollo diagnostic computer. I was reluctant. I assumed the TPS worked similarly to a fuel sender, but I wasn’t familiar with parameters and I don’t think I ever stumbled upon them either.

  10. In the ECU loom I have bare wire. Has absolutely no insulation on it at all. It has some gold Mylar looking foil wrapped around it in some places. It runs through the firewall into the engine bay loom and is bare for most of its run there too. It’s not connected to anything on the ecu side. Just makes a loop and runs back into the loom. What the heck is it?

  11. Heyo, I’ve got an 87 4.0L, seems like the ecu is not even getting power. It will crank but not start, fuel pump doesn’t turn on and I don’t get spark. Do you know what wire into the ecu should be receiving power? (I’ve seen conflicting answers online). Some of the ports read less than a volt, but nothing reads 12V.

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