Spark Delay Valves (Sdv) - Mityvac MI8000 Benutzerhandbuch

eXhaust Gas recircuLation (eGr)
SERVICE PROCEDURES
1) Remove the air cleaner and plug the intake
manifold fitting. Start the engine and bring it to
normal operating tempera ture. Position the fast-idle
cam follower on the second step of the fast-idle cam
(to obtain about 1500 RPM), and then note engine
speed on a tachometer. Use the pump to check the
source vacuum at an intake manifold port (FIGURE
8). Note this reading.
OPERATION
Spark Delay Valves (SDV) are used to delay vacuum
to the distributor vacuum advance actuator during
hard accelera tion, to delay the action of the
Thermactor Air Induction Reaction (AIR) system
during prolonged engine idling, and to delay the
application of vacuum to the automatic choke
pulldown diaphragm during cold engine operation.
A sintered metal valve is installed in the vacuum
advance (outer) diaphragm of the distributor con-
trol unit on some engines. The purpose of the valve
is to delay the spark advance during rapid accelera-
tion to minimize the formation of NOx. The sin tered
metal is porous and allows vacuum to bleed through
the valve acting like an orifice of about
.05 mm (0.002") in diameter. Control is obtained
Attach the Pump Here
Transducer
Exhaust Gas Inlet
FIGURE 8: TEST THE VACUUM SOURCE FOR
THE BPV WITH YOUR PUMP
Form 824357

sparK DeLaY vaLves (sDv)

ERG
Valve
2) Tee your pump into the vacuum pas sageway to the
BPV and the reading should be 35 to 70 mbar (1 to
2" Hg) of vacuum. Replace the BPV if it is not within
specifications.
3) Leave the vacuum gauge at this location, remove
the hose to the EGR valve, and plug the hose open-
ing. Read the vacuum pump gauge, which should be
the same as the intake manifold vacuum reading.
If it is not within 70 mbar (2" Hg) of the source
vacuum, replace the BPV valve.
by varying the number of discs in each valve
assembly so that the time delay features can be
tailored to the engine (FIGURE 9).
SERVICE PROCEDURES
The time delay of the valve varies with engine
application. The different valves may be identified
by color and part number. Spark delay valves can-
not be repaired and must be replaced every 12,000
miles because the pores of the sintered metal fill
with dust, which can slow the performance of the
valve. NOTE: The spark delay valve is a one-way unit
that must be installed with the Black side facing the
car buretor vacuum port.
FIGURE 9: TYPICAL SPARK DELAY VALVE
Spark
Delay
Valve
Page Number - 13