Fleetwood FWD V8-300 4.9L (1993)
EGR Valve: Description and Operation
Exhaust Gas Recirculation
SYSTEM OPERATION
The Exhaust Gas Recirculation (EGR) system is used to lower NOx (oxides of nitrogen) emission levels that are caused by high combustion
temperatures. The EGR system introduces exhaust gas into the air/fuel mixture, to reduce combustion temperatures. The reduced combustion
temperatures help to lower NOx emission levels. The main elements of the system are the EGR valve and EGR solenoid. The EGR valve is mounted on
the intake manifold, and is vacuum operated. The solenoid is mounted on the engine valve cover and controls the amount of vacuum to the EGR valve.
Positive Backpressure EGR Valve
EGR VALVE
This vehicle uses a positive backpressure EGR valve. A positive backpressure EGR valve requires exhaust backpressure (proportional to engine flow) to
open and allow exhaust gas to 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, the engine might misfire. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle. Careful
diagnosis of the system is important so that outside conditions (such as an exhaust tube connected to the vehicle causing reduced exhaust backpressure)
will not lead to misdiagnosis.
The EGR valve is usually open under the following conditions:
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Warm engine operation.