Mityvac 06820 Diesel Compression Test Adapters - Manual (Page 14)

Page Number - 14
Form 822378
SERVICE PROCEDURES
1) Start engine, run at idle until it
reaches normal operating tempera-
ture.
2) Make sure the intake manifold hose to
the amplifier is properly connected.
On those systems with a reservoir,
remove the hose from the reservoir
and use a tee connector to join the
hose to the intake manifold vacuum
hose.
3) With separate lengths of hose and
different connectors, bypass any and
all vacuum valves or coolant con-
trolled valves between the amplifier
and the EGR valve.
4) Use a tee connector to attach the
pump into the vacuum line between
the amplifier and EGR valve.
5) Increase engine speed to 1500/2000
RPM and release the throttle. Let the
engine return to idle speed and
remove the vacuum hose at the
carburetor Venturi. The vacuum
reading should be within ± .3” Hg of
the specified boost for that amplifier if
other than zero boost is specified.
Zero boost may read from 0 to .5” Hg.
Replace amplifier if out of specifica-
tion.
6) Increase engine speed. Watch
vacuum gauge and release accelera-
tor after speed of 1500/2000 RPM is
reached. If the vacuum gauge reading
shows an increase greater than
1” Hg during acceleration period, the
amplifier should be replaced.
7) Remove the pump from the output
vacuum line and reconnect hoses, but
still bypass other valves. Connect the
pump and apply 2” to 4” Hg of vacuum
to port on the amplifier which is
normally connected to intake manifold
vacuum. The EGR valve should
operate and engine idle should drop
or become erratic. If the EGR valve
fails to move, replace the amplifier.
EGR VENTURI VACUUM
AMPLIFIER
Some engines utilize a Venturi Vacuum
Amplifier that uses the weak vacuum sig-
nal from the throat of the carburetor to
allow the passage of the stronger intake
manifold vacuum to operate the EGR
valve. On most applications the amplifier
provides a 2” Hg boost to the Venturi sig-
nal (FIGURE 8).