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Vehicle Speed Sensor... How important is it to TBI???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TruckNutzDude, Dec 19, 2005.

  1. TruckNutzDude

    TruckNutzDude 1/2 ton status

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    I'm considering doing a custom dash w/ no speedometer (off road only... who cares how fast you're going when you can walk next to your rig) I've got an '89 K5 w/ TBI and I know there's the green speed sensor box attatched to the back of my speedometer. I'm not planning on using the factory gauges and I'd hate to mess up my engine by not having an important sensor there. I've got an SM465 transmission, no ABS brakes and no cruise controll. I do mash the skinny pedal from time to time since I am living behind a swamp and things get deep quickly. Can I remove the sensor without damaging my rig with normal operations going from idle to WOT on a regular basis?
     
  2. ryan22re

    ryan22re 1/2 ton status

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    as far as i know, the speed sensor is there just to tell the computer about converter lockup. but it will set the check engine light. (you might not have one after the custom dash). but, it may be good to be able to see the check engine light, so if something did go wrong you could see it. personally, id leave the cable hooked to the box, and just hide it behind the new dash/gauges.


    ryan
     
  3. TruckNutzDude

    TruckNutzDude 1/2 ton status

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    I never thought about the check engine light. It comes on all the time because of my O2 sensor not being plugged in... which probably means I'm in open loop or "limp" mode. :rolleyes: :doah:
     
  4. btolenti

    btolenti 1/2 ton status

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    All I know is the VSS controls the tranny lockup, EGR and the EVAP canister purge. Stealth Conversions also says that it control the A/F ratio and idle speed. You could always go with an aftermarket VSS. Painless makes one that goes on the transmission speedo output.
     
  5. TruckNutzDude

    TruckNutzDude 1/2 ton status

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    I didn't know it did so much but I knew it did something. I may just keep the stock gauges and add some aftermarket ones. I don't like spending money to replace something that I already have, especially if it works. My gauges work (except the oil pressure one since it spins around and around and around... makes me dizzy) I was just looking to get rid of the entire dash when I installed the roll cage. I like a nice sparse interior for when I hose it out after a day in the pits.
     
  6. Thunder

    Thunder 3/4 ton status

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    If you aren't runnng an 02 sensor your VSS is the least of your worries.
    Without 02 sensor input the ECM ignores and overides all other sensor input except TPS, MAP,& CTS. and runs on pre programed operating parameters. or "Limp Home"
    You can run without a VSS. The only problems it usually causes is poor idle or stalling and the torque convertor wont lock up
     
  7. TruckNutzDude

    TruckNutzDude 1/2 ton status

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    My O2 wire isn't plugged in, I only drove on it once like that and I broke the t-case adapter that day so I haven't driven it since. I noticed it was unplugged when I got home to look at the 'case and driveshaft (which also broke that day) I've got all sorts of projects going on with the K5 and sometimes I forget a wire or two... :crazy:
     
  8. Thunder

    Thunder 3/4 ton status

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    Beings your rig is offroad. You can prolly get away with ditching the VSS. It wont hurt to run without one. Some people have no problems with out VSS others have idle problems. Best thing I can say is. after you get your 02 sensor fixed try unplugging the VSS and see how it runs.
    You can also get a chip programed to ignore the VSS if you want. Anyone who burns chips can do it for you.
     
  9. 425 Xpedition

    425 Xpedition 1/2 ton status

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    If the computer thinks the vehicle is in park or neutral it does not look for an input from the VSS. If I remember right all you do is ground the park/neutral input to the computer. Had to do this before on an TBI engine swap. Never set any codes and worked great. When I did finally put a VSS on the truck I could not tell any difference in performance.
     
  10. btolenti

    btolenti 1/2 ton status

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    You can definitely run with it grounded, but your EGR will be inoperative and could cause detonation, per the JTR TBI swap book.
     
  11. 425 Xpedition

    425 Xpedition 1/2 ton status

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    Yea I remember reading the JTR book when I did the swap. It had a lot "scare" stuff in it, saying this and that won't work. Sometimes I wonder who writes those books. Alot of the TBI swaps in older chevy in this area do not use a VSS input. Most people don't know about the VSS adapters that can be bought from JTR.
     
  12. btolenti

    btolenti 1/2 ton status

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    Yeah, I really didn't use the JTR book as much as I thought I would. If I did it over again, I wouldn't have bought it in the first place. I think it's a better book for those adapting a chevy TBI/TPI to a non-GM vehicle. The TBI swap in a K5 is pretty easy as long as you have wiring & vacuum diagrams.
     

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