Ford VSG-411 Service Manual page 69

03A-5 Emission Control Svstem
03A-5
DESCRIPTION AND OPERATION (Continued)
EGR VALVE (CLOSED)
A DIAPHRAGM SPRING
B VACUUM NIPPLE
C PINTLE
D INTAKE MANIFOLD
E EXHAUST GAS
F MANIFOLD VACUUM
G PINTLE SEAT
H DIAPHRAGM
A DIAPHRAGM SPRING
B TO VACUUM
C PINTLE
D INTAKE MANIFOLD
E EXHAUST GAS
F MANIFOLD VACUUM
G PINTLE SEAT
H DIAPHRAGM
The EGR vacuum port is open to vacuum when the throttle
plate is opened slightly (off idle). Vacuum is then available
to the EGR control valve. Vacuum level decreases as the
throttle plate opens.
At closed throttle, the EGR port is blocked from vacuum.
At wide open throttle, EGR vacuum is weak to zero and
will cause the EGR valve to close for maximum engine
power. Note that at idle (when EGR vacuum is off) the
EGR system is least needed because NOx formation is
at a minimum.
THROT TLE PLATE
(OFF IDLE
POSITION)
HIGH VACUUM
FLOW TO EGR
HlGH INTAKE++
MANIFOLD VACUUM
m VACUUM
Under certain circumstances, the EGR valve will usually
be off. These include:
1.
At idle, when the engine needs a richer mixture.
2. When the engine is cold.
3.
When there is a heavy load (wide-open throttle).
At idle and at wide-open throttle, there is no vacuum at the
EGR vacuum port. To control EGR at various engine
temperatures,
a port vacuum switch (PVS) is used.