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Thread: MFI and Relay HELP!

  1. #1

    MFI and Relay HELP!

    I have a bad relay, which has something to do with a mechanical switch on the MFI of my 73 911S. It sits on the board next to the rear window defroster relay. On deceleration, the little mechanical switch closes and the relay is supposed to cause a change in the fuel/air mixture. My relay failed, and now my beautiful car (with a brand new $1000 Leistritz muffler) backfires constantly like an old jalopy. The part number is 901 615 113 00. Porsche lists it as a good part number, but no one seems to have one. Do any of you have a source for one of these parts?

    Silver Surfer
    '73 911S Sunroof Coupe

  2. #2
    Check the general info board...
    Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
    "Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)

  3. #3
    Early 911S Registry # 237 NeunElf's Avatar
    Join Date
    Nov 2002
    San Dimas, CA
    If this is a pure relay, and not a g sensor or throttle position sensor or something, you ought to be able to replace it with some sort of generic 12V relay.

    If you want a period correct looking relay, you could check with:

    NLA Limited, Inc.
    P. O. Box 41030
    Reno, NV 89504-5030

    Work: 775-626-7800
    Fax: 775-626-1220

    NLA mainly supports 356s. My 1965 911 has so many parts in common with 356s that I call them fairly often. I'm not certain a long-wheelbase 911 is so 356 like.

  4. #4
    the mirco switch is used to cut off the fuel supply when the engine speed exceeds 1600? rpm and the gas pedal is at the idle position.

    the schematic for the control is floating on this board and there are a few members here that can repair your 'box'. take the cover off and check for smoked components.

    i am not sure if the control box cuts the juice to the fuel pump or activates a cut off solonoid on the rack. pelican has a check measure adjust pdf file and the wiring diagram is on a thread on this board. search away.

    i have a t and never could get mine to backfire with the switch disconnected. you should also check for exhaust leaks which can also cause an overun backfire.
    72 911t * 74 914 2.0

  5. #5


    Thanks to all. You have been very helpful. I changed out my RPM transducer, and the car runs much smoother now. I still get some backfiring, but seemingly less than before, so I will continue to search for a complete solution--maybe an exhaust leak as Tryan suggested.

    Silver Surfer
    '73 911S Sunroof Coupe

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