Mityvac MI8000 Manual Del Usuario página 12

eXhaust Gas recircuLation (eGr)
Always check whether there is vacuum at the hose
connected to the EGR valve, before replacing the
valve. Connect the pump to the vacuum supply
hose at the EGR valve and check whether at 2000
RPM there is at least 130 to 170 mbar (4 to 5" Hg)
vacuum avail able. Remember also that clogged
exhaust passages that lead to or from the valve can
restrict the flow even if the valve is opening.
An EGR valve that remains open will cause the
engine to idle roughly, die at idle, and lose power
and full-throttle smoothness. Dirt or damage in the
valve seat area usually cause the valve to fail. An
EGR valve can operate nor mally with the engine
warm but remain open when the engine is cold.
That condi tion could be caused by a faulty thermal
switching device that does not cut off the vacuum
supply when the engine is cold.
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 65
mbar (2" Hg) boost to the Venturi sig nal.
SERVICE PROCEDURES
1) Start the engine, and run it at idle until it reaches
normal operating temperature.
2) Make sure the intake manifold hose to the
amplifier is properly connected. On those systems
with a reservoir, remove the hose from the reser-
voir and use a tee connector to join the hose to the
intake manifold vacuum hose.
3) With separate lengths of hose and dif ferent
connectors, bypass any and all vac uum valves or
coolant controlled 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 to 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 ±10 mbar (± 0.3" Hg) of the specified boost
Page Number - 12
for that amplifier if other than zero boost is
specified. Zero boost may read from 0 to 17 mbar
(0 to .5" Hg). Replace amplifier if it is out of
specification.
6) Increase engine speed. Watching the vacuum
gauge, release the accelerator after a speed of
1500 to 2000 RPM is reached. If the vac uum gauge
reading shows an increase greater than 35 mbar
(1" Hg) during acceleration period, the amplifier
should be replaced.
7) Remove the pump from the output vac uum
line and reconnect the hoses, but still bypass other
valves. Connect the pump and apply 65 to 130
mbar (2 to 4" Hg) of vacuum to port on the ampli-
fier 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.
BACK-PRESSURE TRANSDUCER VALVE
(BPV) OPERATION
The Back-pressure Transducer Valve (BPV) controls
the amount of EGR accord ing to the load on the
engine. An exhaust pressure probe extends into
the exhaust crossover passageway to sample the
exhaust gas pressure. During light engine loads,
the pressure in the exhaust pas sageway is relatively
low, while during wide-open throttle operation
(WOT), the pressure is highest. This pressure signal
is transmitted to a diaphragm in the BPV and is used
to control the amount of vacu um applied to the EGR
valve (FIGURE 7).
To Distributor
Spark–
EGR Thermal
Vacuum Valve
Exposed to Exhaust Gas Pressure
FIGURE 7:
EXHAUST BACKPRESSURE TRANSDUCER VALVE
To EGR
Valve
Form 824357