Pontiac Fiero 1988 Service Manual page 692

D R I V E A B I L I T Y A N D E M I S S I O N S - F U E L INJECTION (PORT) 6E3-C7-1
SECTION C7
I XHAUSTGAS RECIRCULATION (EGR) SYSTEM
CONTENTS
GENERAL DESCRIPTION C7-1
PURPOSE C7-1
OPERATION C7-1
ELECTRONIC VACUUM REGULATOR VALVE C7-1
PORT EGR VALVE C7-1
EGR VALVE IDENTIFICATION . . . . . . . . . . C7-1
RESULTS OF INCORRECT OPERATION . . . . C7-2
GENERAL DESCRIPTION
PURPOSE
The exhaust gas recirculation (EGR) system is
used to lower NO
x
(oxides of nitrogen) emission levels
caused by high combustion temperature. It does this
by decreasing combustion temperature.
The main element of the system is the EGR valve
operated by vacuum and mounted on the intake
manifold.
The EGR valve feeds small amounts of exhaust
gas back into the combustion chamber as shown in
Figure C7-1.
OPERATION
The EGR valve is opened by manifold vacuum to
let exhaust gas flow into the intake manifold. The
exhaust gas then moves with the air/fuel mixture into
the combustion chamber. If too much exhaust gas
enters, combustion will not occur. For this reason,
very little exhaust gas is allowed to pass through the
valve, especially at idle. The EGR valve is usually
open during warm engine operation and when the
vehicle is above idle speed.
The amount of exhaust gas recirculated is
controlled by variations in vacuum and the EGR
vacuum control solenoid.
E L E C T R O N I C V A C U U M R E G U L A T O R V A L V E
The electronic vacuum regulator valve (EVRV)
uses "pulse width modulation" to control EGR flow.
This means the electronic control module (ECM) turns
the solenoid "ON" and "OFF" many times a second
and varies the amount of "ON" time ("pulse width") to
vary the amount of EGR.
The ECM uses information from the following
sensors to enable the EVRV:
• Throttle position sensor (TPS)
• P/N Switch
• Manifold absolute temperature (MAT)
DIAGNOSIS C7-2
O N - C A R S E R V I C E
C7-2
EGR VALVE C7-2
EGR M a n i f o l d Passage C7-3
ELECTRONICVACUUM REGULATOR VALVE C7-3
EVRV FILTER REPLACEMENT . . . . . . . . . . . C7-3
P A R T S INFORMATION . . . . . . . . . . . . . C7-3
[T| EGR VALVE QQ
INTAKE AIR
fT] EXHAUST GAS [T] EGR VACUUM PORT
4S 0001-6E
Figure C7-1 - Exhaust Gas Recirculation
The ECM uses information from the following
sensors to regulate the EVRV:
• Engine Load
• Coolant Temperature
• Distributor (rpm Signal)
• Torque Converter Clutch (TCC)
A diagnostic switch is part of the control and
monitors vacuum to the EGR valve. This switch will
trigger a "Service Engine Soon" light, and set a Code
32 in the event of a vacuum circuit failure.
P O R T EGR V A L V E
The port EGR valve (Figure C7-2) is controlled by
a flexible diaphragm which is spring loaded to hold
the valve closed. Ported vacuum applied to the top side
of the diaphragm overcomes the spring pressure and
opens the valve in the exhaust gas port. This allows
exhaust gas to be pulled into the intake manifold and
enter the engine cylinders.
EGR
V A L V E IDENTIFICATION
• Port EGR valves have no identification stamped
after the part number (Figure C7-3).