Cherokee 2WD L4-126 2.1L DSL Turbo VIN B FI (1986)
Fig. 20 EGR dump valve
EGR DUMP VALVE
This valve, Fig. 20, is used on some vehicles and is connected between the EGR vacuum signal source and the EGR valve. It prevents EGR operation
when intake manifold vacuum drops to 3-5 inches Hg, by ``dumping'' the EGR vacuum signal.
THERMAL VACUUM SWITCH
The Thermal Vacuum Switch (TVS), used on some models, is located in the air cleaner and functions as an On-Off switch controlled by temperature
in the air cleaner. The TVS controls the vacuum passage between the EGR valve and the CTO switch. When the temperature reaches below 40° to 50° F,
the TVS restricts vacuum to the EGR valve and deactivates the EGR system, thereby improving cold weather performance.
FORWARD DELAY VALVE
This valve, used on some models, is installed between the CTO switch and EGR valve and functions to delay the total force of the vacuum applied to
the EGR valve. By gradually applying vacuum to the EGR valve, a sudden activation of the EGR system is avoided. When installing a new delay valve,
position the black painted side toward the EGR vacuum source.
REVERSE DELAY VALVE
This valve, used on some models, is installed between the CTO switch and the manifold vacuum source. This valve functions to retain the manifold
vacuum applied to the distributor vacuum advance mechanism when the engine is cold and is rapidly accelerated. This action prevents the ignition timing
from retarding. When the engine coolant reaches a specified temperature, the CTO switch will go to ported vacuum.
