Confusion with "VSS" connection and Dakota system

Discussion in 'High Tech Retrofits' started by Goat, Mar 27, 2018.

  1. Goat

    Goat Veteran Member Lifetime Gold Member

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    A lot of you already know this, but to recap, I am using the GM engine harness, along with a Painless whole car harness, Vintage Air, and a Dakota Digital dash/harness to run my LSX/T-56 Magnum. Integrating these different systems can be confusing because there are so many options. There is a "VSS" wire in the GM harness that I believe is an input and not an output. I need to know what to do with this wire to get the speedometer on my Dakota gauges to work.

    To add to the confusion, in addition to the stand alone Dakota kit, I also bought one of their "OBD" units. This has a connector/software that allows you to plug into the GM OBD connection making it even easier to capture signals - but only some of them. Dakota says that "speed" is always one of the signals available through this port. But, reading in the GM manual, it is not clear to me if the "VSS" wire in the harness needs to be hooked up (they make it sound almost optional) to something and if so, to what?

    It makes sense to me that the VSS "wire" probably needs to get some sort of signal for the ECM. Doesn't make sense that the ECM could determine vehicle speed from just engine outputs...

    My guess would be that the "VSS" wire needs to connect to the transmission output, but I can't find anything to verify that...

    Wanted to stop here first to see if anyone with a Dakota system could help before calling Dakota tomorrow. Last time I asked them a question they acted like I was bothering them or something...
     
    Last edited: Mar 27, 2018
  2. John Wright

    John Wright Veteran Member Lifetime Gold Member

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    The VSS is in the transmission and creates a small current of its own (square wave). This needs to be wired to the VSS in at the ecu.

    Edit: the only concern is the ECU is looking for a certain "count" per mile to understand what speed you are traveling. May already be set, or you may have to edit the tune in the ecu to correct it. 2k per mile in the T56, I "think".
     
  3. badazz81z28

    badazz81z28 Veteran Member

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    Yes, the connector on the harness is an input to the ECM. BTW...it likely has the wrong connector on it for the T56 magnum. You need to swap it out with the correct Ford connector. The single output wire for a gauge is in the bulk head connector. You can either wire that to a gauge or you can use the GMLAN wires to read data from the ECM. You’ll see these wires are coming out of the OBD II connector. I recall they also terminate in the bulkhead connector.
    https://m.ebay.com/itm/Vehicle-Speed-Sensor-Connector-Rear-Standard-S-699/323170379186?fits=Make:Ford&epid=1067950656&hash=item4b3e74a5b2:g:qx0AAOSw1CBZ4nNo


    I’m using a auto meter gauge. So I calibrate the signal to the gauge not the ECM. With the Tach you will see you need to add a resister or splice that wire with another pin in the ECM connector for it to work.

    Your ECM does needs the VSS signal. That’s how the reverse lockout is going to operate and the ECM knows when your moving for airflow control. It’s an important aspect for proper tuning. One tuner I spoke to wouldn’t even touch a car without a operating VSS.
     
    Last edited: Mar 27, 2018
  4. greencamaro1981

    greencamaro1981 Veteran Member

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    the computer can be tunes to any input pulse per mile, very important for idle control.
     
  5. Goat

    Goat Veteran Member Lifetime Gold Member

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    Thanks all for your help once again.
     
  6. badazz81z28

    badazz81z28 Veteran Member

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    Yup tire size is a common tune change.
     
  7. Goat

    Goat Veteran Member Lifetime Gold Member

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    Thanks for the tip on the connector, but I had already picked one up from American Powertrain. Also, with the Dakota system, I can just pick the speed signal right off the OBD connection, along with engine temperature, and whatever else the OBD has to offer.
     
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  8. badazz81z28

    badazz81z28 Veteran Member

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    Well that's what the bulkhead connector is for. Youre not plugging it into the OBDII are you?
     
  9. Goat

    Goat Veteran Member Lifetime Gold Member

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    Yep. That's what it is designed to do. I talked to Dakota today. I could use the bulkhead connector, but it becomes a little less clean. For one thing, the connectors are different - 16 pin vs. 12 pin. And there is no engine temp signal in the bulkhead connector...
     
  10. badazz81z28

    badazz81z28 Veteran Member

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    The wires in the bulkhead are the same wires as what’s in the OBDii.

    GMLAN High and GMLAN Low. They come out of the ECM and go to the OBD and extra wire is pinned with the OBD wires to come back out to the bulkhead.

    All your info is coming from 2 wires...my only question is how are you going to tune the car if the OBD is plugged into you gauges?
     

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