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  •  » Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

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    Yesterday 3:25 PM  #1

    gkm24
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    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 115

    Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Just fitted an Auto Meter speedo in my 66 with the EFI and AOD mod but not sure about wiring it up. Auto Meter state that the "Ford E9TZ-9E731-A" speedo sensor needs the low wire  grounded and the Hi side signal wire connected to the Speedometer. Thats easy enough,
    I am happy to do that but if the ECU needs a VSS (Vehicle Speed sensor) signal, does it need a pos and neg and if so, can I just wire it the same way as the speedometer?
    Thanks for any help.

     

    Yesterday 5:19 PM  #2

    50vert
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    From: QLD Australia
    Registered: 4/01/2013
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    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    What ECU setup are you using? I guess a ford OBD1 ECU. Even my computer controlled AOD-E doesn't have a VSS input to the ECU.
    If you have something exotic, I think the autometer speedo has a VSS pass through.

    "Those telephone poles were like a picket fence"
     

    Today 2:05 AM  #3

    gkm24
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    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 115

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Thanks for your reply. You are correct in the ECU model. I just assumed  from the wiring diagram that as the ECU was shown with pin 6 -ve and 3 +ve for VSS that it needed the signal. Happy days if thats not needed then and I will just wire the speedo.

       •Thread Starter
     

    Today 3:50 AM  #4

    50vert
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    From: QLD Australia
    Registered: 4/01/2013
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    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Just to double check, (I didn't make my harness) I'd wait for second opinion from someone running a Fox ECU.
    I know that Dan (Nos681), uses a VSS with a cable on his Fox swapped car, he'll be along shortly.
    Was it a running car before the speedo swap?

    "Those telephone poles were like a picket fence"
     

    Today 5:58 AM  #5

    gkm24
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    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 115

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    The whole thing is a refit of engine box speedo etc... Everything works fine but no signal to the speedo as I have the sensor connected to the ecu.
     

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    Today 11:31 AM  #6

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,571

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    https://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif


    The Ford VSS connects to ECM pins 3(+) and 6 (-).
    Cruise control or a speedometer that requires the use of the VSS just taps into the same ECM pins.

    Assuming you are still using the A9P ECM.

    My ‘92 had the ECM and factory cruise control module share the single VSS signal.

    Last edited by Nos681 (Today 11:42 AM)

     

    Today 11:38 AM  #7

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
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    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    In simple terms, the VSS generates a signal the ECM uses for making adjustments.
    Having the correct speedometer gear could make a difference too.


    Last edited by Nos681 (Today 2:42 PM)

     

    Today 11:39 AM  #8

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
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    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

     

    Today 2:37 PM  #9

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,571

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    I looked up Auto Meter instructions and bottom of page 3 appears to be your application.
    Read the note about connecting to the High signal wire.
    I would not ground the Low signal wire.
    I believe the ECM does it internally.

    I used Summit Racing listed instructions:

    https://static.summitracing.com/global/images/instructions/atm-3989_instructions.pdf



    Last edited by Nos681 (Today 2:38 PM)

     

    Today 3:28 PM  #10

    gkm24
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    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 115

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Thank you for that. I do have it wired as in the diagram for 2 wire no computer involved. I will recheck the calibration as I know that I have not run the car for the recommended 2 mile distance yet. I guess if the ECM earths the signal, its all covered correctly but Auto Meter say that the HI side signal wire goes to the speedo. Is that the +ve wire or -ve wire or does it not matter. If it doesn't work I can swap it round I suppose

       •Thread Starter
     

     

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