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TBI VSS Signal

Discussion in 'The Injection Section' started by G.M.H, Jun 22, 2005.

  1. G.M.H

    G.M.H Registered Member

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    I am putting a tbi setup from a 1990 suburban(came with 700R4?), into a 1980 blazer with a th-350 trans.I have an autometer electric sender #5291 that puts out 16 pulses per revolution (square wave).Will this signal satisfy the ecm? If not, is there a speed sensor that will screw onto the th-350 that will work?
     
  2. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I do believe the TBI uses a 4 pulse per turn signal. I am sure there are plenty of different aftermarket VSS that you could buy and install for a TH350. If not a factory one (not sure when they stopped using TH350s)
     
    Last edited: Jun 23, 2005
  3. G.M.H

    G.M.H Registered Member

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    What vehicle,if any,would have came from the factory with fuel injection and a th-350 trans?
     
  4. sweetk30

    sweetk30 professional hooker Premium Member

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    i used the tail shaft and tonering from the 700 in my th350 swap. worked great. 2x4 truck.
     
  5. tunedportk5

    tunedportk5 1/2 ton status

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  6. dyeager535

    dyeager535 1 ton status Premium Member

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    (edit: I'm ONLY talking about our trucks, not the '88+ body style)

    1990-91 use the 40 pulse VSS for output to the DRAC. ECM still wants 2000PPM. All '89-previous trucks use 2000PPM cable drive VSS at the speedometer.

    '82-89 (I'm not POSITIVE on the '82, my '83 was) all use cable drive speedo with VSS, just get a speedo from one of those years and put it in your '80. Should be an exact fit for the one in there now.

    No TH350 and FI, if the 700R4 tonering works as stated, you could use that. jagsthatrun.com also sells a bolt on "exterior" tone ring, but I don't like that idea for a truck that sees offroad use at all, even weeds would mess it up mounted to the pinion like they show.

    The earlier VSS/speedo setup would make your swap a whole lot easier and cheaper though. Just make the speedo read the correct speed.
     
  7. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Actually, a stock VSS on the back of a speedo is a 2ppt setup. I am using one for my TPI. Like mentioned it is almost a bolt in thing. You'll need to dremel out some plastic off the back of the housing, but otherwise the mounting points are the same.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    2PPT?

    1000 cable RPM X 2 pulses every cable revolution=2000PPM
     
  9. Mastiff

    Mastiff 1/2 ton status Premium Member

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    FWIW, you don't have to use a VSS at all. I retro'd my 83 with EFI with no VSS. It all seems fine to me. I'm not 100% about whether chip mods are required if you don't have it though.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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  11. G.M.H

    G.M.H Registered Member

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    Thanks,but I have a '54 willys body on the truck and cannot use any stock speedo. The autometer speedo I have is programmable from 500 to 250,000 pulses per km,so it should not pose a problem. It has input-output terminals so it can be wired inline with an existing vss-ecm wire. the problem is getting the proper signal for the ecm. The autometer sender has a passthru drive, so I could run another sender or cable off of it. This will all run off the np205 t/c actually , not the th-350. If I do not run a vss,I believe I have to ground the park wire so the ecm thinks it is in park all the time, correct?
     
  12. sweetk30

    sweetk30 professional hooker Premium Member

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    i ran my old truck for a few months with a 4l80-e in it and no speedo hooked up to the truck computer or speedo. i used a stand alone setup. worked o.k. no problems with it. dont need to put wire to ground.
     
  13. G.M.H

    G.M.H Registered Member

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    How can I tell which sender my ecm uses? I have the sender,but it will not fit my t-case.It has a purple wire and a green wire twisted together, which go to the DRAC module.I will order one from JTR if I know which one to order.The dealer will only give me a new part #.I need to know if it is the 2000 pulse unit or the 4000 pulse unit.
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    The DRAC needs 40 pulses per output shaft revolution, thats what you'll need.

    This IS a 2wd application, right? Never saw it mentioned.
     
  15. G.M.H

    G.M.H Registered Member

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    No, it is a4x4,the sender mounts in the t/case.I was not planning on using the drac.My autometer speedo will buffer the signal.
     
  16. G.M.H

    G.M.H Registered Member

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    Just an update for anyone searching this later. I got the sending unit from painless wireing to run that tbi ecm.(autometer says theirs will only run the speedo,not the ecm) One wire (either one) goes to an ecm ground and the other goes to the brown drac or vss wire on the ecm (A-10 terminal)
    In my case that one goes thru the autometer speedo (no drac required).I clocked two miles with my GPS on a long straight street to program the speedo, and it seems to be nearly right on now. The truck runs nicely now, except for a slightly fast idle, probably a vacuum leak.
     
    Last edited: Sep 22, 2005

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