Vacuum/ electric thing
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hello,
That is the TCS solenoid. (Transmission Controlled Spark)
It's part of an early version of emissions control.
Regards.....
That is the TCS solenoid. (Transmission Controlled Spark)
It's part of an early version of emissions control.
Regards.....
Last edited by Alan 71; Sep 28, 2025 at 08:29 AM.
Thread Starter
Racer
Joined: Aug 2006
Posts: 288
Likes: 11
From: South of Chicago Illinois
found this on a Chevelle forum. Also explains the temp sensor in the passenger head with 2 outputs on it, and a relay on the firewall. “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.
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.
