Mityvac 06820 Diesel Compression Test Adapters - Manual (Page 16)

Page Number - 16
Form 822378
2) Record the vacuum reading, which
should be between 10-16” Hg.
3) Pinch off the vacuum hose and
observe if the gauge maintains the
vacuum level. If the gauge shows
that the vacuum drops with the hose
pinched off, the gauge or vacuum
hose has an external leak, which
must be corrected.
4) Now, connect the Black side of the
spark-delay valve to the vacuum
hose leading to the carburetor spark
port. Connect a section of vacuum
hose to your vacuum pump and
attach the other end to the distributor
end of the spark delay valve.
Observe the time in seconds for the
gauge to reach 6” Hg, with a 10-16”
Hg vacuum source. If the vacuum
reaches the 6” Hg level in less than
two seconds, regardless of type, the
SDV should be replaced. When
checking the valve, care must be
taken to prevent oil or dirt from getting
into the valve as this will impair its
function.
ELECTRICAL/VACUUM SOLENOID
SERVICE PROCEDURES
1) Disconnect vacuum and electrical
connectors from the solenoid.
Connect the pump to port “B” and
attempt to apply vacuum with pump.
Vacuum should be released through
port “A” (FIGURE 12).
2) Using jumper wires, connect negative
solenoid terminal to ground and apply
12 volts to the positive terminal. Apply
vacuum to port “B”. Vacuum should
hold and not bleed off. If the solenoid
does not hold vacuum, replace
solenoid.
3) With solenoid still energized, move
vacuum pump to port “A”. Attempt to
apply vacuum. Vacuum should be
released through the air filter and no
vacuum should be present at port “B”.
THERMAL-CONTROLLED VACUUM-SWITCHING VALVES
SERVICE PROCEDURES
These control valves are called Ported
Vacuum Switches (PVS) when used on
Ford engines. Thermal Ignition Control
(TIC) valves when used on Chrysler
products, and Distributor Thermal
Vacuum-Switches (DTVS) when used on
General Motors engines.
The two-port valve is used to stop EGR
while the engine is cold. This type of
thermal switch is needed to provide good
driveability by limiting the entrance of EGR
until the engine is warmed up.
The three-port valve is commonly called a
cooling system PVS because it switches
the vacuum source to the distributor from
ported to full intake vacuum.
The four-port valve has been used in some
Ford engines to bypass the spark delay
valve and cut out the EGR system when the
engine is cold.
SERVICE PROCEDURES
Follow this procedure to test the two-port
vacuum-switching valve:
1) Apply 10” Hg of vacuum to the bottom
port of the valve with your vacuum
pump and measure the results with a
second vacuum gauge as shown in the
accompanying illustration (FIGURE 13).
2) The valves are color coded and the
Green valve should open and pass
vacuum at 68° F, the Black valve at
100° F.