TCS L34 Troubleshooting [Archive] - Chevelle Tech

: TCS L34 Troubleshooting

Jun 4th, 08, 8:53 AM
My TCS suddenly stopped working properly. I have stock 1970 L34 with M21. The system will not advance the timing in 3rd or 4th gear. Car runs fine without it, but it ran fine with the system working and I'd like to make it operational again; for originality. What steps should I take to determine cause for malfunction? All vacuum hoses are new and fuse is OK.

Steve S
Jun 4th, 08, 1:02 PM
Assuming you have a diagram of the circuit I would do the following.
1. With key on, pull the green wire off the Temp Override Switch.
Touch the green wire to ground, should here the Override Relay click
With the green wire on ground, verify that there is 12v on the DK Blue wire to the Vacuum Control Solenoid.
This verifys wether that the override relay is working correctly

2. To test the Vacuum control solenoid, ground the green wire, remove the black wire from the trans switch and ground it. This should energize the vacuum control solenoid. With the car running remove vacuum hose from dist and you should have manifold vacuum.

3. Tap into the black wire from the trans switch to the Vacuum control solenoid. Put a test light where you can see it while driving - +12v on one side and black wire tap on the other. Drive the car until it is at operating temp and in high gear, light should come on, if not something wrong with trans switch wiring or the switch itself.