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Opel Kadett 3100 V6

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  • Opel Kadett 3100 V6

    I brought my 1978 Opel Kadett back from Europe a few years ago with the intent to do a V6 and 5 spd swap. I din't do ant work for about a year but gathered parts and did some research. I got a lot of great information and advice from folks on this site but then got to spend some time overseas so the project sat again for a while. Now I finally got around to actually doing some work.

    For the engine, I bought a 3100 out of an 01 (I think) Grand Am that was running in a sand rail using a 7727 ECU. In the rail, the engine was bare bones- alternator only, no PS, no AC, manual trans which is how I'll run it in my car. The upeer and lower intake are reversed and I'm using a RWD tining cover and water pump. The wire harness was stripped down to only the required switches/sensor/etc but the harness needed some cleanup.

    Before I finish the harness, I want to make sure I have all the required connections and sensors. It is is my understanding that the 7727 ECU does not use a cam position sensor so I can remove that from the harness. One thing that does concern me is the cam position sensor (just behind water pump with red green and black wires) connector is different from the connector in the harness (see pic of connector in hand with pink/black and black wires). I assume this is because I am mixing cars/years/ECUs but would appreciate clarification from one of the experts on this board.

    Question 2- Does the 7727 ECU require the oil pressure sensor (lower front/left side of block near the knock sensor)? If not, I'll use that port for my oil pressure gauge sender.

    3. What wires from the 7727 control the fuel pump relay/provide power to the fuel for prime and run? I'll be using an external Walbro pump.

    4. What is the connector in the second pic? I assume it is a diagnostic port to read codes but would like to confirm

    Thanks again for any help.
    Attached Files
    Last edited by 63a16p; 03-20-2016, 10:19 PM. Reason: Added pics

  • #2
    The cam sensor wiring can be completely removed so there's no concern there about wire colours or locations. Just don't connect it to anything. I just leave the sensor in place to plug the hole, others will find a Welch plug to plug the hole.

    2. The oil pressure sensor should control the fuel pump relay, in the event that the ECM does not for whatever reason. There's a few different wiring schematics for the oil pressure sensor circuit, but I believe that all '7727 equipped vehicles used the oil presure sensor to control the fuel pump relay in addition to sending the information to the gauge. You should be able to find the wiring diagrams online. I know that they are hosted at

    3. Again see the wiring diagram for the fuel pump relay control wire.

    4. Yes, the second picture is the ALDL connector.
    James: 1985 GMC Jimmy, 3.2L turbocharged, intercooled hybrid 13.873 @ 99.08 218HP & 270FT/lbs @ the wheels
    The Daily: 2000 GMC Yukon
    1973 Datsun 240Z: Turbo intercooled LX9, running on '7749 with $59 and DIS. 12.71 @ 115

    "If you're not living on the edge, You're taking up too much space."

    Still waiting for the 1st or second Ostrich I was promised, from Paul.


    • #3
      Thanks for the help.

      Regarding the 7727 ECU- does it matter what vehicle came from or are they all the same pin-out and wire color? I have no idea what car my ECU came from unless that can be determined by any numbers/codes on the housing.

      I'm sure I'll have more questions after I look at the right schematic. Looking at the schematic for the donor engine ECU was a bit confusing with the 7727 wiring.


      • #4
        After looking over a 92 Lumina 3.1 wiring diagram which I think is a 7727 ECU, I cannot find an oil pressure sensor but I do see the fuel pump and relay schematic. Based on the wiring harness I have, it looks like the previous owner did have the oil pressure sensor in the loop.

        On to more research...


        • #5
          image.jpegI think I've figured out most of the wiring but still a few questions-

          1. Any idea about the connector in the pic? It is in the 3100 engine harness and has a pink/blk wire and black/wire which was connected to ground in previous install. I can't locate an appropriate connector on the engine so looking for any ideas.

          2. I think I understand the idea about supplying signal to the fuel pump relay through the oil pressure sender so the fuel pump stops if oil pressure drops. However, I'm not sure where the relay gets signal for fuel pump prime. The wiring diagram I'm using (92 Lumina) shows a wire going to "fuel pump prime connector" but I don't know what/where that is in the harness. If anybody has a wiring diagram for their fuel pump/pumps with a 7727 ECU, I would appreciate it. I'm planning to use a low pressure/high volume pump at the tank to supply the high pressure pump (Walbro) underhood. I'm not set on running the fuel pump signal through the oil pressure switch- are there any pros/cons to going through the oil switch? I assume the oil pressure switch is relatively reliable but would appreciate advice/input on fuel pump wiring.

          3. I'm installing a non VSS T5 so I don't have a sender for the VSS. Can I leave VSS disconnected or should I add a resistor in the circuit to mimic the signal that would be produced by the VSS?

          Thanks for the help


          • #6
            On 1 that looks like the ignition module power connector.

            On 2 the pressure switch gets wire in parallel with the fuel pump relay so that a bad relay doesn't cut power to the fuel pump. If you suddenly have to crank the engine for a long time to start the car your fuel pump relay is bad- When oil pressure builds up to make the switch it powers the fuel pump.

            On 3 I'm very surprised that your T5 has no provisions for a speed sensor. How was the speedometer run in it's original vehicle? The VSS input expects a series of pulses corresponding to your speed so a resistor isn't going to cut it.


            • #7
              Thanks for the info, do you mean the ignition module that is part of the coil pack or is there a spa rate ignition module elsewhere in the system.

              2. That makes sense- will leave pressure sensor in the loop

              3. T5 is from 88 Camaro with mustang tailhousing to get shifter in right position. The speedo is a cable drive but will check if ford used a VSS on any cars that could be used. What affect would leaving the VSS out of the system have on the engine?



              • #8
                I agree, wire colours and connector look like ICM power connection.

                Without a VSS, the engine will not idle or return to idle as stable as it could with a VSS, there's also some other functions that are more behind the scenes that may not work well without a VSS input. A VSS is easy to connect, so I recommend adding one. There are several ways to do this from using stock to aftermarket parts.
                James: 1985 GMC Jimmy, 3.2L turbocharged, intercooled hybrid 13.873 @ 99.08 218HP & 270FT/lbs @ the wheels
                The Daily: 2000 GMC Yukon
                1973 Datsun 240Z: Turbo intercooled LX9, running on '7749 with $59 and DIS. 12.71 @ 115

                "If you're not living on the edge, You're taking up too much space."

                Still waiting for the 1st or second Ostrich I was promised, from Paul.


                • #9
                  .3 Go to JTR web site and order item #3 for your vss. It's what I use and works well.



                  • #10
                    Thanks for the help. I found the ICM power connector- just overlooked it before.

                    For the VSS, I looked at the JTR part but it won't work since I'm using a Mustang tailhousing on my T5 and Ford uses a different speedo cable connection. Some Fords do have a VSS that goes between the speedo cable and trans but I need to do some research to determine if the Ford VSS produces the appropriate signal for the GM ECM. If the Ford VSS is a no go, I'll look at more creative solution. Maybe I can fabricate an adapter to adapt the JTR VSS in-line with a GM to Ford speedo cable.


                    • #11
                      Based on my internet research so far, it doesn't like the part I need is available off the shelf. Also, I think the Ford VSS provides a different pulse-rate signal so that won't work. Since I already need to graft the Opel speedo cable to the Ford speedo cable, I'll add the VSS adapter inline somewhere between the firewall and transmission. Do any GM cars have a VSS with a cable pass through (like the JTR #3 mentioned above) I can find at the pick-a-part. Considering I may ruin the adapter (or a few) in the experimentation/fabrication process, I'd prefer to ruin cheap parts.


                      • #12
                        I don't know exactly what the ford signal looks like but this may help you adapt it.


                        As long as the PPM or Pulses Per Mile is within a power of 2 then I haven't had problems. It may be even more tolerant than that.


                        • #13
                          I can use a Ford VSS (8000ppm) that will fit in the T5 tailhousing and has a speedo cable output which I can adapt to the Opel speedo cable. I know the 7727 ECM is looking for a 4000ppm VSS signal. Will the 8000ppm signal "confuse" the 7727 EM since my VSS speed will be 2x actual vehicle speed? At low speed, the difference won't be significant but at highway speed, VSS speed will be quite high.


                          • #14
                            Or just use a stock GM T5 reluctor wheel and put it in the ford transmission.


                            • #15
                              I don't know how the ford signal "looks" compared to the GM one but I'd try to change the value in the ECM to match the 8000PPM signal. This is what I did with my older GM 2000PPM signal and the 7730 (non waterproof cousin to your 7727).