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Speed sensers and TBI?

Discussion in 'The Garage' started by blazen91, Oct 4, 2002.

  1. blazen91

    blazen91 1/2 ton status

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    I am building a trail only truck and am using a stock TBI 454. As I understand, the fuel injection needs a speed senser, which in the speedometer. I want to get rid of the speedo. Does the fuel injection need the speed senser, and if so, is there way to ditch the speedo and use some other kind of speed senser? Thanks.
     
  2. azblazor

    azblazor 1/2 ton status Premium Member

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    You can run a speedo cable to a VSS box and leave it at that, don't connect an output cable to the speedometer. As to whether the computer "needs" the speed signal is debatable. I run a speed signal on both my conversions - there are several programs that are designed to use the signal. BUT - the engine will function and run reasonably well without the speed signal. If you care to do a few searches there has been much discussion on this topic in the past.
     
  3. u2slow

    u2slow 1/2 ton status

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    Depends on the year of the donor truck. If the engine (and therfore ECM) came with a 4L80E transmission you will need the speed sensor.

    The easiest bet is to get an ECM from an 87-90 truck with a TH400 or SM465 - i.e. a truck that used a cable-drive speedo.
     
  4. FWP

    FWP CRS

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Does the fuel injection need the speed senser

    [/ QUOTE ] Yup, sure does....

    </font><blockquote><font class="small">In reply to:</font><hr />
    is there way to ditch the speedo and use some other kind of speed senser?

    [/ QUOTE ]
    Depends on the ECM, 87-90 TBI you can get adapters from JTR and others for about 85-90 bucks. The best place I've found to research the info you need is on thirdgen
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Those ECM's still had a VSS input. It was provided by an optical sensor that was installed in the speedo head itself. /forums/images/graemlins/shocked.gif
     
  6. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">Yeah for TBI you need the optical VSS in the speedometer.
     
  7. u2slow

    u2slow 1/2 ton status

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    That optic sensor is strictly for cruise control. Its that little green box that plugs into the back of the speedo. Non-cruise trucks don't have this sensor.
     
  8. HarryH3

    HarryH3 1 ton status Author

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    The 1987 GM Factory Service Manual shows that the VSS signal always goes to the ECM. It states that the VSS is mainly used to control TCC lockup, shift light (for manual trannies) and cruise control. So it apparently wasn't used just for cruise control.
     
  9. u2slow

    u2slow 1/2 ton status

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    Well that kind of makes both of us right /forums/images/graemlins/wink.gif

    The '89 1-ton 2wd crewcab I wrecked out did not have the green box, since it was a TH400, and non-cruise. This is the ECM that ended up in my buddy's Jeep running a SM465/Dana 300 - and no electronic speedo. It was the last of six different ECMs he tried.
     
  10. blazen91

    blazen91 1/2 ton status

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    Thanks all for the input. It came out of a 88 one ton truck with a 400/205 combo and no CC. So am I correct in the majority saying "no" so I don't need it?
     
  11. BurbinOR

    BurbinOR 3/4 ton status

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    I'd run it regardless. I started out with my TPI conversion without VSS and it ran great.........put the VSS in because it's cheap and easy and it runs great..........with better idle quality. /forums/images/graemlins/tongue.gif
     
  12. BILLY RAY

    BILLY RAY 1/2 ton status

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    Ok here is an easy fix. This is what I did to mine it is a TBI 350 but the same thing. There is a orange wire with a black tracer on my unit ( stock unit ) that comes out of the PCM if you ground it the PCM will not look for the speed sensor signal because it will think it is always in park. Nice cheep trice hu!!!!!!!!!! Hope this helps. /forums/images/graemlins/thumb.gif
     
  13. blazen91

    blazen91 1/2 ton status

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    Why does the TBI need the speed senser? What is it reading? /forums/images/graemlins/1zhelp.gif
     
  14. zcarczar

    zcarczar 1/2 ton status

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    Mike, I got this out of my '89 factory service manual.
    The vehicle speed sensor is located behind the speedometer or transmission, "CK" or "P" series, sends a pulsing voltage signal to the ECM, which the ECM converts to miles per hour. This sensor mainly controls the operation of the TCC system, shift light, and cruise control.
     
  15. blazen91

    blazen91 1/2 ton status

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    Why does the TCC need to know the speed?
     
  16. zcarczar

    zcarczar 1/2 ton status

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    I think on trucks like mine with the 700R-4 it tells the tranny when to lock up the torque convertor. Because on mine sometimes it locks really early like under 50 mph, or if im getting on the freeway it wont lock up till 75 or 80 mph. But the 400 you have shoudlnt be computer controlled if I remember correctly. I'll have to ask the guys at my work on this one, but I dont think you need to run the VSS.
     

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