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Can someone explain TCS

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by JST12, May 14, 2001.

  1. JST12

    JST12 1/2 ton status

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    I'm thinking I have extra wiring I don't need. There was this solenoid on the original carb with three wires. I think the schematic says it's "TCS". Also there are two relays on the firewall near the brake booster which seem to be tied into this circuit. And there is the wire that goes to the auto trans (not kickdown, because that is a cable) . What does this stuff do? Is it for AC idle increase? Anyone?
    Thanks,
    JT
     
  2. BobK

    BobK 1/2 ton status

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    It's supposed to help with emmisions.I believe it prevents the distributor from advanceing the timeing untill you've hit a certain speed or gear.It's something like that anyway.I have all that on my 71(all the wireing that is)Most guys just take it off and don't worry about it.Some states may have laws against that so if you do take it off don't throw it away...you may need it in the future.

    [​IMG]<font color=green>BobK<font color=green>
     
  3. 2quicK5

    2quicK5 Registered Member

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    TCS (Trans Controled Spark advance) was an emissions control item. Under some driving conditions and trans gears, such as coasting down a hill, it disabled the vacuum advance mechanism on the dist. The solenoid on the carb let the system know when you had your foot off the gas and was coasting. On some models there is also a solenoid to increase idle speed when the A/C is turned on. The TCS solenoid basically just has a switch. This 'emissions' junk reduces the performance and gas mileage of your vehicle and should be removed and discarded unless you live in the communist utopia of Kalifornia.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  4. JST12

    JST12 1/2 ton status

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    Thanks guys! Awesome. Those wires are coming out! Just to be clear, do you know if the single wire going to the auto trans is only for the TCS or is there some other purpose? It will be cleaner to rip that puppy out too. Thanks again. JT
     
  5. ErikH

    ErikH 1/2 ton status

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    Even in Kalifornia you can dispose of the TCS, or any other SMOG part for that matter. The rules only apply to '73 and newer vehicles. That's why I have all hi-perf on my '71.
     
  6. 2quicK5

    2quicK5 Registered Member

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    Jeff,

    The single wire coming from the trans tells the TCS system what gear the tranny is in. You won't need it anymore so go ahead and rip it out too.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 3" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  7. Steve_Chin

    Steve_Chin 1/2 ton status

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    I know a bit about the emissions systems, since i have to maintain smoggability on several of my cars that are heavily modified. No part of the TCS system is hooked directly to the carburetor as a sensor. It is a very simple system that has a switch located on the transmission and a valve that controls vacuum to the distributor. The switch on the transmission in combination with the TCS valve/solenoid prevent any vacuum from reaching the distributor unless the transmission is in top gear. When the transmission is in top gear, the switch shorts and provides a ground path to the TCS valve/solenoid, which allows vacuum to reach the vacuum advance canister. If the transmssion is not in high gear, the TCS switch is open and the TCS valve/solenoid switches the vacuum can to atmospheric pressure. The solenoid itself should be mounted to the intake manifold on the passenger side, toward the rear (to the bolt/stud).

    Some years TCS systems included wither thermal valving as a bypass or an electric thermal switch that bypasses the switch in the transmission. The thermal switch will bypass the TCS switch in the transmission when the engine is either too hot or too cold. The theory there is that a cold engine needs a little more RPM to help warm it up (at idle) and a hot one needs a little more RPM to move more air through the radiator (and has little to do with emissions).

    The A/C system has a separate fast idle solenoid that should attach to the front of the driver's side of the carburetor. When the A/C is off, it is inactive, and when the A/C is on, it opens the throttle blades and provides apx. 1100-1300 RPM unladen idle speed (less with the compressor functioning).
     
  8. JST12

    JST12 1/2 ton status

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    Thanks for the great explanation. This info really helps. Looks like I can use the existing brown wire for the TCS carb switch, which has power when ignition is hot, to power my electric choke. It's really going to clean up the engine bay by cutting out 10 useless wires, sensors, and solenoids. See ya, JT
     
  9. Blazer1970

    Blazer1970 1/2 ton status

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    As Steve said, there is no switch on the carb having to do with the TCS system. That said, I used the hot wire that went to the TCS relay on the firewall to power my electric choke.

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  10. JST12

    JST12 1/2 ton status

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    Man, I wish I had a decent schematic . I'll check again, but I know there is the solenoid on the original carb which has a three wire plug going to it. Steve said there is not a sensor on the carb, but there is the solenoid with a switch which when electrically activated dumps the vac going to the distributor. The colors of the wires match my schematic. Looks like the same brown/white wire at the time delay relay on the firewall is the wire at the solenoid by the carb I am planning to use. Of course the wires could be for the AC idle solenoid which is not even in my schematics. That was one of my original thoughts above. JT
     
  11. Blazer1970

    Blazer1970 1/2 ton status

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    If you are talking about the solenoid that mounts to the intake manifold next to (not on) the carb, that is the TCS solenoid that controls the vacuum to the advance canister on the distributor, like you said.

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  12. JST12

    JST12 1/2 ton status

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    Thanks for all the input. I have enough info to make the wiring changes. I've ohmed and traced the wiring. It appears to have all the components listed in Steve's and your messages, but the configuration is different. I cannot say whether my 71 Jimmy is different than a 70 or 72 Blazer, but the fact is mine has the solenoid ON THE CARB which has an electrical socket, a vacuum line going to the dist vac advance, and a vac line coming from a port on the carb. this switch is wired into the relays on the firewall, trans sensor, etc.. It is TCS but a different version than others it seems. Let's let this thread die finally. Thanks again. JT
     
  13. Steve_Chin

    Steve_Chin 1/2 ton status

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    JST12: I just wanted to point out that a previous owner or a mechanic could have moved the position of the TCS solenoid at some time in your Jimmy's life between the time it left the factory and now. According to the literature I have, the factory was supposed to mount the thing to the right side rear of the intake manifold. It is a good thing tha you traced all of the wires and found out what the purpose of this piece is. Good luck.
     

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