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89 TBI transmission switch

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BadDog, Dec 29, 2001.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I have a square, 4 conductor plug (only 3 wires) that, according to my schematic, should go to a switch on the auto trans. It seems to let the ECM know when the tranny is in 3rd and 4th gear (also has temp dependencies). Needless to say, there is no place for this in my TH400. Does it matter? Should I hard wire it in some way to fool the ECM? TIA.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  2. 95 Silverado

    95 Silverado 1/2 ton status

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    that sounds very much like the plug that fits a 700R4 transmission, was the turbo 400 the original tranny in your truck, maybe someone swapped in the 400 in place of a 700R4, it's all related to the lock-up torque convertor so you won't need it with the 400.

    '95 Chevy Silverado 1500
    5.7 V8-NV4500- 3.73 rears
    See My Toys: &lt;a target="_blank" href=http://community.webshots.com/user/wdb172454&gt;http://community.webshots.com/user/wdb172454&lt;/a&gt;<P ID="edit"><FONT class="small">Edited by 95 Silverado on 12/29/01 01:39 PM.</FONT></P>
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Hehe, no, I pulled the TBI 350 from an 89 Sub and grafted it into the CUCV in place of the 6.2 diesel and I'm using the Subs 89 TBI harness. I'm using the diesel TH400 from the CUCV and, yes, the Sub had the 700R4.

    I'm just trying to figure out if I should do anything with the plug to keep the ECM happy. I'm thinking it might be good to jump 2 of the wires together to make the ECM think I'm always in low (schematic shows the "open circuit" to indicate 3rd/4th gear) due to the dedicated off-road use.


    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  4. 95 Silverado

    95 Silverado 1/2 ton status

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    on my 700R4 two of the wires are used for the convertor clutch, power in and ground(the ecm supplies the ground to lock/unlock it)the third wire goes to a normally open switch that grounds when in fourth gear( the signal for the ecm). so if you leave that wire ungrounded the ecm will think it is not in 4th gear

    '95 Chevy Silverado 1500
    5.7 V8-NV4500- 3.73 rears
    See My Toys: <a target="_blank" href=http://community.webshots.com/user/wdb172454>http://community.webshots.com/user/wdb172454</a>
     
  5. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Cool, thanks for the info. It was not obvious from the schematic exactly how it worked. I'll just tie that thing back out of the way...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     

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