In looking to put a temp sensor for radiator fans I found a switch/sensor in the passenger side head where there is normally a plug. I have the temp gauge sensor in driverside head, what is the switch/sensor in the passenger side head. It is above and between the rear two spark plugs on the passenger side head. Thanks for any help available.

 

TCS switch?

 

yep TCS switch, you don't need it and don't want it... so use the hole there for your temp sensor...


sully

 

Thanks for the infor, but what is a TCS switch and what is it used for?

 

tuned control spark or something like that.... when you shift into 4th gear it keys the soleniod on the carb and the switch on the passenger head to adjust the vaccuum advanced, i think it retards it, therefore giving better economy...I don't think it ever actually worked very well and it is completely useless...

Sully

 

Here you go!!

It is a pretty simple system. The vacuum that would be available to the distributor vacuum advance is controlled by a solenoid valve. At idle and in neutral, the TCS solenoid valve blocks the vacuum to the distributor vacuum advance and vents the distributor vacuum advance to atmosphere. In 3rd and 4th gear, a switch mounted on the transmission applies power to the the TCS solenoid and thus provides manifold vacuum to the distributor vacuum advance. So, there is no vacuum advance in 1st or 2nd, but only in 3rd and 4th. This was done for emmisions.
In addition, there is a two terminal thermal switch mounted in the passenger side head. When the car is first started and if the temperature is cold enough, one half of the thermal switch, the low temperature switch, will close and activate the TCS solenoid so as to provide vacuum for spark advance for a cold engine, for improved idle and idle speed. Once the engine begins to warm up, that thermal switch will open and the system will go back to normal operation.
If the engine temperature gets too hot, say while you are idling in traffic, the other half of the thermal switch, the high temperature switch, will close and activate the TCS solenoid to provide vacuum advance so that the engine will cool some. Once the engine temperature falls below the high temperature switch limit, the high temperature switch will open and the system will return to normal operation.
This is how the factory system is set up. Of course, after all these years, your particular car may have been modified to bypass some or all of these functions. I hope this helps.

 

The TCS when energized would not allow vaccum advance in the first 3 gears. When you shifted into 4th gear and the temperature was up to normal the solenoid was kicked off allowing vaccum to the dist giving it full vaccum advance for better fuel economy. It was a poor design and did not work very well at all. Most all but NCRS cars have long gotten rid of the system.

Damn! he was quicker than me. That explains it all.

 

Note that I stated that the factory TCS system provided advance in both 3rd and 4th gears, but not 1st and 2nd. I owned a 70 BB many years ago when the car was still pretty new, and the system worked flawlessly. Not sure how much it actually helped emissions, and it sure affected performance in 1st and 2nd, but the electro-mechanical-vacuum system worked very well.

 

Thanks very much gentlemen for the information. If I understand correctly removing the wiring and sensor should have no affect on the engine performance, hot or cold.

 

Are you saying it was better performance or worse performance. Under full load in any of the gears there is no vacuum advance anyway. It was just under light throttle of cruise that vacuum advance comes in.

Just reading over the GM manual on this TCS system. It does only work in 4th or high gear. The Corvette was the only GM car tha tused the low 82 and high 232 switch. So the thermal head switch is a Corvette aprt only. All others just used the low 82 degree switch. The LT1 Corvettes used full manifold vacuum and all others used ported vacuum for the distributer. The system also used a 20 second delay timer so it had to be in 4th or high gear and the temp had to be between 82 and 232 and 20 seconds would have elapsed before it would allow vacuum to the distributer.

 

If you have a copy of the 1970 Chassis Service Manual, it has a diagram and charts on page 6T-2 that shows the TCS system. It clearly shows that the system provided vacuum advance in 3rd and 4th gears in cars with 4spd transmissions. Indeed, this is how my 70 BB was set up from the factory. The diagram shows no time delay, and as I recall, there was no delay in my vehicle.

What I was saying about the effects on driving was, that because there was no advance in the lower gears, you could feel it as you drove.

 

They may have changed it in 72. My manual is a 72. They were always trying to improve it but we all know it was a luaghable system. Interesting how the different years changed systems.

 

My only experience is with the 70, but I seem to recall that I have read where there are differences in other years, so I am sure you are correct that the 72 might be set up differently. You are also correct in that most everybody disconnects this system, since it was for emissions, and better performance and mileage can be had without it. Plus, quite often, items are missing from the original system, like the solenoid, temp. switch, and relay.

r44s--Sorry if we sort of hijacked your thread.

 

No Problem, good info. Still wondering about performance. Although the distributor vacuum hose goes directly to the carb. Thanks

 

You will get better performance running the car without the system. Run vacuum advance on the street. Setup properly it will provide good performance and better economy than the TCS system.

 

Thanks for all the help, the sensor is removed and awaiting the radiator and temp switch. Next weeks project.

 

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