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EFI relay, Uphold Relay, and Mystery relay

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  • EFI relay, Uphold Relay, and Mystery relay

    Directly rear of the fusible link holder there are three relays hidden inside the fender well. They are covered by a plastic flap, and visually covered by the battery. EL-104 of the 87 FSM gives a picture of two relays: A EFI relay (which is green) and a Uphold relay (which is black).
    On my 87NA there is another relay next to the green EFI relay on the same wiring harness. I believe its orange. What is it and what does it do?
    What circuits does the EFI relay relate to specifically? Obviously it plays some role in the fuel injection system...
    What does the Uphold relay do?
    I have had a few electrical problems recently...There is a good possibility they might be related to these relays.

    *Note: I have seen these relays be other colors besides orage, green and black...

    "produce second."

  • #2
    Interesting. I looked in my 84 and 85 FSMs and they also only show 2 relays. EFI and Uphold. I remember seeing an orange relay somewhere but now I'm not recalling which one it was.

    The Uphold relay is for the headlamp motor.
    Just stand back and throw money.
    Performance costs money.
    Reliable performance costs more.


    • #3
      I would also like to know more about the EFI relay. My injectors are not pulsing because they are not getting a ground, so I am wondering if the EFI relay might have something to do with this.

      Note: For Fuel Pump Circuit Testing, The FSM suggests disconnecting the 15 pin harness from the ECU to test wire #108 for voltage with the ignition on. When I disconnect that harness, I hear a loud buzzing coming from the area where the EFI relay is hidden. Kinda strange?


      • #4
        Im going to take a stab in the dark. AZ-Bum made mention at one point that there is a relay close to the battery that cuts power to the EFI system should you cross terminals on the battery (guilty as charged).

        Not sure if I remember it correctly. Maybe he can chime in. I'm not entirely certain but I don't think he was talking about the Fusible Links.


        • #5
          A buddy of mine was doing his na2t swap and on the first start he hadn't tidy-ed up his wiring harness. It melted to the exhaust manifold while running and shut itself off. When we were trying to figure out what happened there was a relay going NUTSO in the fender area and was grounding out due to the wires being melted together.
          Start checking out your harness!
          "Its the s12's sexy over weight step daughter, the z31"


          • #6
            There is a neon green "EFI relay" mounted inside the fender between the strut mount and the battery. It is the only green relay afaik. I bought a car with a parasitic drain, it was an 84T car with an 87 ecu. This relay clicked when the car was off. I replaced the relay, nothing. When I replaced with an 84T ECU, no drain, and everything functioned properly.


            • #7
              there is also a passing relay for the hi beams and a car alarm relay

              its probably the passing relay which turns the hi beams on when u pull the lever towards you
              it doesnt stay on you have to keep them on manually and you can always turn them on no matter what position your headlight switch or motors are in
              We choose to do things not because they are easy but because they are hard.


              • #8
                Anyone have a pic of the relays and how they're set up?

                I asked a Nissan Tech friend.

                He's off work for a few days, and he'll check into it .. but was wondering if anyone had a photo.
                '84Z31 GLL turbo|theZenthusiast site: |

                Originally posted by maronee
                PS - by the way your Z31's famous here in japan, dude!!


                • #9


                  • #10
                    According to the ECCS Wiring Diagram, the EFI Relay powers the following:
                    Crank Angle Sensor
                    Air Flow Meter
                    Pressure Regulator Control Modulator
                    Pressure Regulator Control Solenoid
                    EGR Control Solenoid
                    Idle Up Solenoid Valve
                    FICD Solenoid Valve

                    It gets constant power from a brown wire at fusible link, and when ecu wire 6 completes circuit, efi relay powers up the components listed above, which are all tied into wires #35 and #27 at the ecu.


                    • #11
                      This is a strange coincidence, but I decided to unwrap my ecu harness to check it out. After I took note of the changes that were made (campaign wiring maybe?) I put it back together and checked for power and ground at the ecu. I had a good ground but pins 27 and 35 (battery voltage) were dead. I traced the wires up to the EFI relay and sure enough It had power on three legs but not the 4th one, which goes to the ECU. I jumped the relay, got power to the ECU, but it still won't run.


                      • #12
                        You have power to the ecu but is power coming out? As in are your injectors receiving 12v?
                        "Its the s12's sexy over weight step daughter, the z31"


                        • #13
                          if you know what color wires come in and out of the relay you can trace them through the wiring diagrams and find it I'd bet.