EXHAUST GAS RECIRCULATION
TABLE OF CONTENTS
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EXHAUST GAS RECIRCULATION
DESCRIPTION ..........................2
OPERATION ............................2
VALVE
DESCRIPTION ..........................3
OPERATION ............................3
REMOVAL .............................3
INSTALLATION ..........................3
SOLENOID
DESCRIPTION ..........................4
REMOVAL .............................4
INSTALLATION ..........................4
EXHAUST GAS
RECIRCULATION
DESCRIPTION
The EGR system reduces oxides of nitrogen (NOx)
in the engine exhaust. This is accomplished by allow-
ing a predetermined amount of hot exhaust gas to
recirculate and dilute the incoming fuel/air mixture.
A malfunctioning EGR system can cause engine
stumble, sags, or hesitation, rough idle, engine stall-
ing and poor driveability.
OPERATION
The system consists of:
• An EGR valve assembly, located toward the rear
of the engine on the intake manfiold.
• An EGR solenoid, located in the left rear of
engine compartment near EGR valve. The EGR sole-
noid controls the “on time” of the EGR valve.
• The ECM operates the EGR solenoid. The ECM
is located inside the vehicle under the instrument
panel.
• The vacuum pump supplies vacuum for the EGR
solenoid and the EGR valve. This pump also supplies
vacuum for operation of the power brake booster and
the heating and air conditioning system. The pump is
located in the front of the engine block and is driven
by the exhaust camshaft.
• Vacuum lines and hoses connect the various
components.
When the ECM supplies a variable ground signal
to the EGR solenoid, EGR system operation begins.
The ECM will monitor and determine when to supply
and remove this variable ground signal. This will
depend on inputs from the engine coolant tempera-
ture, throttle position and engine speed sensors.
When the variable ground signal is supplied to the
EGR solenoid, vacuum from the vacuum pump will
be allowed to pass through the EGR solenoid and on
to the EGR valve with a connecting hose.
Exhaust gas recirculation will begin in this order
when:
• The ECM determines that EGR system opera-
tion is necessary.
• The engine is running to operate the vacuum
pump.
• A variable ground signal is supplied to the EGR
solenoid.
• Variable vacuum passes through the EGR sole-
noid to the EGR valve.
• The inlet seat (poppet valve) at the bottom of
the EGR valve opens to dilute and recirculate
exhaust gas back into the intake manifold.
The EGR system will be shut down by the ECM
after 60 seconds of continuous engine idling to
improve idle quality.
25a - 2 EXHAUST GAS RECIRCULATION WG
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