TCS Timing Control System Explained For GM Cars and Trucks
TCS or Timing Control Switches are a device found on early 1970’s early GM vehicles. At first glance you might think TCS means Traction Control System, but back then there was no such device.
In short, these Timing Control Switches were a system that would tweak the timing for better fuel emissions. Think of them as an early SMOG control device. The only time you will see them today is in high-end period correct restorations or factory unrestored cars. Almost everybody else rips them off or doesn’t install them back.
Here’s the explanation of the TCS straight from the Chevrolet chassis manual:
“The distributor vacuum advance has been eliminated in the low forward gears as is shown on the chart… The control of the vacuum advance is accomplished by means of a solenoid vacuum switch which is energized, the vacuum source to the distributor is shut off and the vacuum advance unit is vented to the atmosphere by means of a clean air connection to the carburetor air hose. This prevents the vacuum advance unit from becoming vacuum locked at some advance position.
The TCS System also incorporates a temperature override system which provides full vacuum in all gears when the engine is cold for improved drivability. A thermostatic water temperature switch provides the signal which energizes a normally closed relay, opening the circuit to the solenoid vacuum switch, thus providing full vacuum. Some vehicles also have a hot override switch which provides full vacuum to improve engine cooling.
The system may be checked for proper function by connecting a vacuum gauge in the hose between the solenoid and the distributor. Full vacuum should be obtained when the transmission is in gear as indicated on above chart when the engine is warm and running.”
In order for the TCS system to work the car needs to be at operating temperature and in a higher gear and then it will tweak the vacuum advance to the distributor. There’s three major pieces needed to for this all to work.