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S32 fuse for Coils keeps blowing off

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  • S32 fuse for Coils keeps blowing off

    Hi,

    Having a bit of a strange problem on a ABY S2. The Purple fuse for the Coils (S32) suddenly blows randomly. Have tried both new style TFSI coils and the OEM coils with the same result. Changed the ECU as well without any change. Seems like its happening when the engine is warm. The strange bit is that when the fuse blows, and it could happen even when the car is at idle, it keeps blowing until the engine has cooled off a bit. Then the engine can run for hours again before it happens, or minutes.

    Any hints? Could faulty coils or bad earth connection cause this problem?
    '91 Audi S2 Coupe
    '85 Audi 80

  • #2
    Possibly internal short in the fuse box or in the wiring below it.

    This might be helpful.
    http://www.s2central.com/S2_Schematics/ABY_Wiring.pdf

    Last edited by newsh; 13th February 2018, 09:38.

    S2 Coupe 3B Project


    Ur quattro restoration

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    • #3
      http://www.s2central.com/S2_Schematics/S2_Coupe.html

      S2 Coupe 3B Project


      Ur quattro restoration

      S2 Avant

      Boost is the new rock and roll!
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      • #4
        Found the issue. A bit strange, but it seems that the MTFS +12v sensor is feeded from this fuse. Looks like someone has tried to repair the plug for the sensor at some point and failed miserably, as it seems like the pin in the sensor that grounds when the water temperature is too hot, is somehow connected to the S32 fuse pin (+12v supply pin) rather than the pin for the feedback signal to the ECU.. As the engine overheats, the sensor grounds the signal and killing the fuse.

        Strangest error i've seen to this date :-)
        '91 Audi S2 Coupe
        '85 Audi 80

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        • #5
          Well done for finding it!
          That really is a strange fault!

          S2 Coupe 3B Project


          Ur quattro restoration

          S2 Avant

          Boost is the new rock and roll!
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          • #6
            That is very obscure fault indeed, well done for sniffing it out and sharing with us.

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            • #7
              Originally posted by vism View Post
              Found the issue. A bit strange, but it seems that the MTFS +12v sensor is fed from this fuse (Fuse 32)
              Strangest error i've seen to this date :-)
              Probably (or shouldn't) have seen it to begin with. The four pin 3B and ABY MFTSs were fed from Fuse S12 (not S32). Fuse S32 is switched power to the ECU and the coils. Nothing to do with the F76 MFTS directly. The later replacement MFTSs were three pin and did not use a 12V source to operate. Somebody who didn't know what they were doing tried to fix a problem with a work-around (and created a new problem instead)





              REFERENCE: http://forums.quattroworld.com/s4s6/msgs/22584.phtml
              GermanABYMotronicDiagram_Annotated_Combined.jpg

              RS2'd 93 UrS4 5 spd sedan
              94 UrS4 V8 6 spd manual avant

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              • #8
                According to the schematics the S32 splits into the Coil 12v supply, the motronic ECU and one goes to the T8 pin 5 (one of the two round connectors), and feeds the MTFS sensor. Verified with both the schematics and actual wiring.
                Attached Files
                Last edited by vism; 18th February 2018, 09:51.
                '91 Audi S2 Coupe
                '85 Audi 80

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                • #9
                  Originally posted by vism View Post
                  According to the schematics the S32 splits into the Coil 12v supply, the motronic ECU and one goes to the T8 pin 5 (one of the two round connectors), and feeds the MTFS sensor. Verified with both the schematics and actual wiring.
                  You might be right but what you are saying doesn't make sense that switched power goes to Pin 2/R on the MFTS. It should go to Pin 3/+.

                  Your "evidence" would be more believable is if the second part of the MFTS diagram that you added on the right had the Track [69] at the bottom. Just drawing a red line doesn't make it believable.


                  RS2'd 93 UrS4 5 spd sedan
                  94 UrS4 V8 6 spd manual avant

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                  • #10
                    The diagram below accounts for all four pins on the S2's F76 MFTS and none of them are connected to the S32 switched ECU and coil fuse. However, 3/+ is connected to the S12 fuse as suggested earlier. AudiS2F76MFTSWiringDiagramCombined.jpg
                    Last edited by UrS4boy; 18th February 2018, 19:00.
                    RS2'd 93 UrS4 5 spd sedan
                    94 UrS4 V8 6 spd manual avant

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                    • #11
                      AudiS2F76MFTSWiringDiagramCombined_Annotated.jpg Maybe this version is better, with the track numbers in the proper order and the connection between the S32 fuse and the switched ECU power input at Pin T55/27 clearer.
                      Last edited by UrS4boy; 18th February 2018, 22:28.
                      RS2'd 93 UrS4 5 spd sedan
                      94 UrS4 V8 6 spd manual avant

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                      • #12
                        That blue / white wire doesn't go anywhere near the coil feed as Dave says. It goes to ecu pin 46 via connector T8f/5, not T8e/5 which is what you have written
                        Mike

                        http://www.s2-audi.co.uk

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