Transmission Controlled Spark: Operation
When engine coolant temperature and speed sensor are under specified temperature and RPM range, the temperature and speed sensors close electrical circuit to computer. Circuit to vacuum switching valve is closed and coil is energized, turning on vacuum switching valve. See 1974 TEMPERATURE & SPEED SENSOR OPERATING RANGE table .
On 2F engine, vacuum switching valve allows vacuum to act on distributor retard diaphragm. On 4M engine, vacuum switching valve applies vacuum to distributor retard diaphragm and admits atmospheric pressure to advance side, retarding ignition timing. On all other engines, when vacuum switching valve is turned on it cuts off vacuum to distributor advance diaphragm.
NOTE:
Operational description is for 1974 models only. Operational description for 1975-76 models not available at time of publication.
TEMPERATURE & SPEED SENSOR OPERATING RANGE
| Application | Thermo Sensor On At °F | Speed Sensor On At MPH | ||
|---|---|---|---|---|
| 3K-C Engine | 140-212 | 11-36 | ||
| 2T-C Engine | ||||
| Federal | 140-221 | 31-41 | ||
| Calif. | ||||
| Man. Trans. | 140-221 | 16-41 | ||
| Auto. Trans. | 140-221 | 24-65 | ||
| 18R-C Engine | ||||
| Federal | 140-217 | 16-62 | ||
| Calif. | 140-217 | 11-41 | ||
| 4M Engine | ||||
| Federal | 140-221 | 16-62 | ||
| Calif. | 140-221 | 16-65 | ||
| F Engine | ||||
| Federal | 140-208 | 13-41 | ||
| Calif. | 113-217 | 13-41 | ||