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Thread: RPM Sensor

  1. 10-15-2017, 03:31 PM #1
    Simonjjb
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    RPM Sensor

    Hi,

    I have a 1972T and noticed that there is nothing in the place where the diagram indicates a RPM Sensor. Is this normal ?

    Name: Screen Shot 2017-10-15 at 7.14.20 PM.png Views: 946 Size: 131.2 KB
    1968 911L Coupe - Golden Green
    1971 911S Coupe - Gemini Blue
    1973 911S Targa - Signal Yellow
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  2. 10-15-2017, 08:44 PM #2
    422flat6
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    The RPM sensor, sometimes called speed switch, works with the microswitch to send signal to the overrun solenoid on the MFI pump to push the rack forward, which quickly reduces fuel flow to idle, when the throttle is completely closed and the RPMs are below about 1700. It's an emissions/fuel saving device that people sometimes disconnect or remove. If your car is a euro model T that came with carbs then it wouldn't have one. All MFI 72 models had it as far as I'm aware.
    Ben
    2012 997 C2S Platinum Silver
    1972 911T Coupe Tangerine Sold
    2006 Cayman S Speed Yellow Sold
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  3. 10-16-2017, 09:28 AM #3
    Flieger
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    It's not just emissions/fuel savings. It pushes the MFI rack past idle and shuts off fuel so you don't get a bunch of backfires when you are engine braking. Makes it run smoother.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
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  4. 10-16-2017, 09:54 AM #4
    Simonjjb
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    ok- thanks. I'll try to figure out where the wiring for it went.
    1968 911L Coupe - Golden Green
    1971 911S Coupe - Gemini Blue
    1973 911S Targa - Signal Yellow
    1974 914 2.3 - Sunflower Yellow
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  5. 10-16-2017, 02:22 PM #5
    Simonjjb
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    Here are two more pictures that show the missing sensor. You can also see that someone has added a fuse to two wires - Red with white stripe and red with black stripe. Maybe thats the by-pass?
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    1968 911L Coupe - Golden Green
    1971 911S Coupe - Gemini Blue
    1973 911S Targa - Signal Yellow
    1974 914 2.3 - Sunflower Yellow
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  6. 10-16-2017, 03:23 PM #6
    edmayo
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    That's the plug to allow disconnect to rear window defroster
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  7. 10-16-2017, 04:42 PM #7
    Simonjjb
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    Thanks - fuse is missing as well.
    1968 911L Coupe - Golden Green
    1971 911S Coupe - Gemini Blue
    1973 911S Targa - Signal Yellow
    1974 914 2.3 - Sunflower Yellow
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  8. 09-08-2018, 11:23 AM #8
    michael70st
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    Does anyone have a working rpm sensor. The part sown missing. part # 901.602.601.00 (Bosch Part #0.227.990.001) it’s the round unit with A,B,C terminals that reduces the voltage from the coil black purple line to the taco. Fitted to 69/70 911, 912 and I think 914.

    My one is on its way out so I need a good one.

    Please message me if you do or you know a supplier

    Thanks
    Michael
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  9. 09-08-2018, 03:02 PM #9
    Frank Beck
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    Who's on first?

    Just so we're all on the same page... RPM sensor is #3 on the image in Simon's first post.

    '72 didn't use the RPM sensor; only '70- early '71. It was to accommodate the holdover '69 Tach.

    Michael, I've had my butt handed to me on "chasing" a bad RPM sensor before. Just curious what your symptoms are?
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  10. 09-08-2018, 07:00 PM #10
    tom1394racing
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    I have the MFI speed switch, (#5) in the first diagram, available for sale. PM me for details
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress
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