Emission Systems - 1971 (continued)

CEC SOLENOID

The CEC solenoid (Fig 71.7) controls the deceleration rate and routing of vacuum in the distributor. The CEC solenoid maintains a preset RPM during deceleration until the transmission is down-shifted. When down-shifted the circuit is broken to the CEC solenoid, allowing the plunger to de-energize, thus blocking vacuum to the distributor during idle and low gear operation.

COLD OVERRIDE TEMPERATURE SWITCH

The cold override temperature switch (Fig 71-8) is a three way switch. The points can be closed to provide code override, hot light activation, or neutral position. At engine temperatures below 82° F, the bimetal post contacts the "cold" terminal, closing the circuit to the CEC solenoid. At approximately 82° F,, the contact is broken, and the post will remain in the neutral position during normal operating conditions. When the coolant operating temperature exceeds 257" F, the post contacts the "hot" terminal to activate the dash-mounted "hot light."

On some Chevrolets (Corvette and Camaro as previously outlined) two separate temperature switches are used. One switch provides both "Cold" override (below 82° F) and "Hot" override (257" F) which allows vacuum to the distributor. The other switch is calibrated to activate the dash-mounted "hot light" when the coolant temperature exceeds 257" F).

TIME-DELAY RELAY

The time-delay relay (Fig 71.9) is a normally closed bimetallic switch. It is grounded through its housing and complete a circuit from the battery through the ignition switch or from the battery through the ignition switch and CEC solenoid, depending upon engine temperature and transmission gear position.

The bimetallic coil opens approximately 20 seconds after the ignition key is turned on, providing the engine temperature is above 82° F, or for approximately 20 seconds after the engine temperature switch "cold" override points open. Vacuum to the distributor for this time internal improves drive-away and eliminates stall after start tendencies.

REVERSING RELAY

The reversing relay (Fig 71.10) is a magnetically controlled two position switch. In its normally closed position the lever makes contact with the ground terminal and completes a circuit through the CEC solenoid. Contact is broken when the transmission-mounted switch points are close which completes a circuit from the battery through the ignition switch. This circuit sets up a magnetic field in the relays which pulls the points open and breaks the circuit to the CEC solenoid, de-energizing it a blocking vacuum to the distributor advance unit. When the transmission is in high gear, the transmission switch points open, breaking the circuit from the battery through the ignition switch and reversing relay. The reversing relay points close, providing a circuit through the grounded relay to the CEC solenoid, energizing the solenoid and providing vacuum to the distributor advance unit.

TRANSMISSION SWITCH

The transmission mounted spark control switch (Fig 71.11) is a two-way switch actuated by the shifter shaft on manual transmissions, and by oil pressure on automatic transmissions. In low gear(s) the points are closed. In high gear the points open, breaking the circuit to the reversing relay and permitting vacuum to the distributor advance unit.

TROUBLESHOOTING

To troubleshoot the complaints of poor high-gear performance, stumble and stall in hot or cols start, excessive fuel consumption, or exhaust pop during deceleration, test for a possible inoperative CEC solenoid. Before proceeding to the tests, check the CEC system fuse and wiring connections. The fuse is labeled TCS on the cowl under the left side of the instrument panel. If the fuse is inoperative, check the wiring for shorts or opens, the replace fuse before you perform any tests.

TEST PROCEDURES →

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