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what else does vehicle speed sensor control?

Discussion in 'The Garage' started by cheyennesuper, May 22, 2005.

  1. cheyennesuper

    cheyennesuper Registered Member

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    I just installed a 700r w/np208 with a cable driven vss to an 350ci TBI that HAD a 2 wheel drive 700r with an electronic VSS on it.Besides the speedometer not working what else will "not having the electronic VSS hooked up" effect?
     
  2. MikeS

    MikeS Registered Member

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    The VSS actually isn't for the speedometer at all. It's part of the fuel injection system. The VSS tells the computer how fast the truck is going. The computer then uses that info to control lock-up torque converter, EGR valve, idle speed, air/fuel ratio, etc. Not having it can cause stalling problems.

    Here is a good link to some great info on it: (it's a PDF) http://www.jagsthatrun.com/V8-chapters/V8-tpi-Speed-Sensors.pdf

    I'm just learning all this fuel injection stuff in anticipation of putting a TPI in my '72 Blazer. That's the only reason I knew the answer :grin:

    Mike
     
  3. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    , yes, if the 700R4 had a VSS, it was for the speedo as well
     
  4. sled_dog

    sled_dog 1 ton status

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    not really. If its cable driven the cable was the speedo, the VSS mounted to the speedo and was for the computer, not the speedo.
     
  5. sweetk30

    sweetk30 professional hooker Premium Member

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    i swaped a 4l80-e in to my truck. i never hooked up the vss to the truck . i used a stand alone harnness. it ran just as if it would with it pluged in. this on a 88-up 2x4 350 tbi truck. only code was no vss.
     
  6. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    "installed a 700r w/np208 with a cable driven vss to an 350ci TBI that HAD a 2 wheel drive 700r with an electronic VSS on it"


    it would help if he gave the year of the truck
     
  7. sled_dog

    sled_dog 1 ton status

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    would.

    http://www.jagsthatrun.com/

    has cable to wired vss converters. i haven't ordered one yet, but I will be doing so very soon(for my TPI setup with an old 205).
     
  8. cheyennesuper

    cheyennesuper Registered Member

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    painless performance's VSS?

    The truck is a 1973 chevy k5 with a 350 TBI out of a 1989 GMC 2wheel drive pickup.The 700r4/np208 is from a 1986 gmc fullsize jimmy.I put the whole dash,instruments,and all from the gmc pickup.The speedometer used to only run off of an electric vss in the 2 wheel drive 700r4,no cable...Now i need it to run off an np208(from '86 jimmy) that is only cable driven.What exactly makes the speedometer work in the 89 gmc pickup?Will it still tell me how fast im going if I use the vss that Painless performance makes?
    http://store.summitracing.com/default.asp?target=egnsearch.asp&N=400012
    ....without a cable?
     
  9. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    yes, you will need the gears in the t-case to be correct for your tire/gear combo(outputs 1000 rev per mile), then you need the correct cable mount VSS(2 pulse)(1000x2 = 2000), then you need to bypass the drac, since it needs 40 pulse per d/s rev, and outputs 2000 ppm to the speedo
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    If I remember my wiring right, pin A10 on the ECM is VSS.

    Get a 1982-1989 C/K/R/V gauge cluster, it's setup for cable drive VSS. Get the gears in the t-case to read right for tire/gear combo, take the power, ground, and VSS (A10) wires from the DRAC connector, and use them with the '81-89 speedo mounted VSS buffer.

    Only caveat here is what the '89 TBI ECM uses for VSS. If it's a 1227747 ECM which I think it is, no other issues. Some of the later ECM's started using 4 or 40 pulse input, but I *think* all DRAC applications used 2000PPM for the ECM.
     
  11. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    nope, I know for a fact that a 89 C1500(c/k are new body style in 88+) uses a VSS, no cable for the speedo, only the r/v(old body style) still used a cable in 88-89, but VSS in 90-91

    and I know that a 89 2wd tbi c1500 uses a 40 pulse output to a drac, which outputs 2000 pulse to the speedo and ecm, 4000 to cruise, and 128000 to the ABS
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    I just get sick of typing '82-87 C/K, '88-89 R/V, that's the reason I got lazy there with C/K/R?V. Hoped it oculd be inferred thats what I meant since he has the speedometer out of the '89 C/K. Not going to work as is unless he gets something that will convert the 2000PPM to 40 pulse per output shaft revolution, and the earlier cluster is the easiest/cheapest way to go.

    Edited: '89 C/K, not R/V as originally I posted.
     
    Last edited: Jun 5, 2005
  13. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    The speedo on the 89 does not want 40 pulse, only the drac does, so, all he needs is the 2000 pulse output VSS and to bypass the drac, , which in 89 was still seperate from the cluster, all the drac does is convert the 40 pulse to the 2000 pulse the speedo needs(and 4000 for cruise, 128000 for ABS, ect)
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    If he gets a 40 pulse generator/setup, everything else stays as is, since he has the '89 speedometer. No extra rewiring, no bypassing, plug it into the t-case, connect VSS wires from DRAC to it, done.

    The only other option is to go cable, older cluster, and rewire VSS/bypass DRAC.
     
  15. cheyennesuper

    cheyennesuper Registered Member

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    What is "DRAC"?

    What is the Drac?
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    It's the "buffer" if you will in some applications that use a transmission or transfercase mounted VSS. 40 pulse setups.

    Opaque colored box, two connectors on it, not sure where it was mounted in trucks. Two wires from the VSS connector run to it, plus power, ground, cruise, ABS, speedo output, ecm output, etc.
     

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