TRAPPED VACUUM SPARK
Thermal vacuum switch (TVS) is mounted in cylinder head and used to sense engine coolant temperature. Vacuum check valve is mounted between manifold vacuum, distributor and thermal vacuum switch. System maintains high vacuum levels to distributor during cold engine operation and cold engine acceleration.
SPARK VACUUM DELAY
Spark vacuum delay is used on 5.7L V8 engines with Heavy Duty emissions. It is installed between TVS check valve and distributor.
When engine temperature is below pre-set specified value, manifold vacuum signal is routed through check valve to distributor. Ports on TVS are blocked. Check valve will keep distributor vacuum at levels higher than manifold depression during vehicle acceleration.
As manifold vacuum increases, check valve opens and allows distributor vacuum to increase to same level. When vacuum decreases during vehicle acceleration, check valve closes and distributor vacuum will decrease at a rate controlled by internal bleed.
COMPONENT TESTING
Note. Testing information not available.