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TBI swap Question- please help

Discussion in 'The Garage' started by bornreadyk5, Dec 1, 2005.

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To VSS or not to VSS? That is the question.

  1. Its a FACT-no way around it..USE THE VSS

    4 vote(s)
    40.0%
  2. Its a FACT-no way around it..DONT USE VSS

    1 vote(s)
    10.0%
  3. Whats a VSS?

    5 vote(s)
    50.0%
  1. bornreadyk5

    bornreadyk5 Registered Member

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    Got a buddy thats swapping a 1990 350 TBI into a 71 SB Chevy truck. Using a stock harness from donor truck.

    Got everything else covered, except:

    Does he need to use a VSS or buffer?

    What will happen if he doesnt?

    Anyone done this swap? Need some facts here. We have been argueing about it all day. Thanks.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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  3. Thunder

    Thunder 3/4 ton status

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    As Dorans post said you should have the VSS. The ECM looks to see if the vehicle is moving or not to set operating paramaters. Some have done the swap without a VSS with no problems. But most people have had problems like idle quality, stalling and torque convertor lock up.
    I would just do the swap and see how it runs. If you are Not using a 700R4 you dont have to worry about the TC lock up.
    If it aint right you can always get a new chip burned to ignore the VSS. Or buy an aftermarket cable driven VSS for it. Both cost about the same
     
  4. mouse

    mouse 1/2 ton status

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    I would run the VSS based on what I've read. I am ready to install a TBI system as soon as the weather warms up. Like what the other guys said, it will improve low speed performance, or throttle response. Plus, in the setup I've got, the VSS is in the speedo, so its very easy to swap in.

    My opinion is the EGR would be the first thing to consider not using...although it does help mpg a little.
     
  5. bornreadyk5

    bornreadyk5 Registered Member

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    What about using a 87-89 ECM to do the swap with? They dont have provisions for VSS those years. They were cable driven. Sounds good in theory...right?
     
  6. mouse

    mouse 1/2 ton status

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    My system is an '89. wires go from speedo-mounted VSS to 7747 computer under the dash. (two or three)
     
  7. K30CJ

    K30CJ 1/2 ton status

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    I swapped an '89 TBI 350 into my Jeep using the factory harness. It has no VSS and runs great. I may be an exception, but it idles perfect, doesn't stall, and does pretty good on gas. Best mod I've done.

    Do like Thunder said. Just do the swap and see how it runs without it.
     
  8. Thunder

    Thunder 3/4 ton status

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    87-89 have VSS. Its cable driven. Spedo cable goes into the VSS located on the back of the spedo.
     
  9. bornreadyk5

    bornreadyk5 Registered Member

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    10-4 will do. Thanks for the replys.
     
  10. cok5

    cok5 Registered Member

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    No hi-jacking here but I am kinda in the same boat except swapping 88 TBI truck into 85 K5. What do I need to do about the VSS? Do you have to take it off the speedo in the truck or get a speedo out of a 87-91 K5?
     
  11. botboy

    botboy 1/2 ton status

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    Since you're swapping into a 73-86, I'd just grab the later model 87-91 (not OBS) dash that has a built in VSS and it should just plug right into your harness, unless you got the 88 TBI harness from an OBS truck and not an 88-91 R, V 15-3500
     
  12. botboy

    botboy 1/2 ton status

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    Oh, since nobody mentioned it and as far as I know there's no easy way to integrate a VSS into the pre-72 dash, check out www.jagsthatrun.com, for about $80 they have an inline VSS for most OBD-I GM ECM's.
     
  13. cok5

    cok5 Registered Member

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    Well I am unsure about the harness right now. I am gonna pull it from the truck (88 2500 light duty, 6 lug) and see how hard it is gonna be to strip it down. If it is too much I will just get one from Affordablefuelinjection.com
     
  14. botboy

    botboy 1/2 ton status

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    I did the TBI swap onto my '72 Cheyenne (next I have my sights set on an LT1 W/TPI harness), you can see a lot of details and placement stuff on my website below. It took me about 5 hrs to cut everything down to the bare minimum, just have to be patient and good with a soldering iron - if you aren't, buy a buddy who is some beer cause intermittent connections will cause you a world of pain.
     
  15. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Get a VSS from Turbo city. Bolts up to your T/case cable take off. Run the wires to your ECM. Job done.
     
  16. drofdar

    drofdar 1/2 ton status

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    I did the same swap of TBI into my 73 K20. Since my ECM was out of a auto trans vehicle, I sent it to Speed Scene wiring in San Antonio to be reburned. They programmed it with my specs, no egr, sm465, 4:10 and so on. They provided a vss that mounted onto the trans where the speedo cable goes. Pricey when including the harness, but works perfect.
     
  17. K30CJ

    K30CJ 1/2 ton status

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    I'll second that. Solder and heat-shrink all connections. It'll save you headaches down the trail (or road). The TBI engine's harness is pretty simple really. If you have some electrical ability, you can save yourself a lot of $$ and learn something in the process. Electrically, the swap consists mostly of getting 12VDC to all the right circuits. Most of the rest can be left alone.
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    If you've got cruise, you've got VSS already.

    VSS is cable drive until 1989, when the clusters changed to electronic speedometer.

    Any of the '81-91 clusters can be made to work with VSS. ALL electronic cruise, CCC, and TBI trucks had VSS in one form or another. (cable or trans/transfer case mounted)
     
  19. cok5

    cok5 Registered Member

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    Well it did have cruise (not any more though.) Where is the VSS so to speak on it...1985 w/cruise?
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    VSS buffer (what you need for an injection swap) is bolted to the back of the speedometer. Yellow or light green box hanging by three joined wires. There are a few varieties of the VSS buffer, the differences are in the connectors from the buffer to cruise and ecm.

    The buffers and wiring are incredibly easy to find, any carbed, cable drive speedo GM car from '81-up will have one.
     

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