Range Rover P38
EMISSION CONTROL
3
DESCRIPTION AND OPERATION
The EGR valve opens allowing exhaust gases to be
drawn into the air intake manifold. The exhaust gas
replaces a proportion of the air drawn into the intake
manifold. Less air flows through the MAF sensor
which consequently requires a lower electrical current
to maintain its temperature. The change of current is
read by the ECM which calculates the amount of
exhaust gas being recirculated.
The mapping in the ECM monitors the MAF sensor
current changes and alters the signal current supplied
to the EGR modulator, varying the vacuum to operate
the EGR valve. In this way, the ECM controls the
amount of exhaust gas recirculated to maintain the
engine at its optimum operating parameters.
The EGR system does not operate when starting the
engine, at engine overrun or when the engine is at full
load. The ECM may also prevent EGR system
operation if the electrical signal from the MAF sensor
is insufficient or if a given speed or injection volume is
exceeded.
Vacuum pump
The vacuum pump is located at the front of the engine
on the cylinder head. The pump is sealed to the
cylinder head with a sealing ring and secured with two
bolts.
The pump is driven from the camshaft via two drive
dogs which engage with corresponding slots in the
end of the camshaft. Engine oil is supplied through a
nozzle in the end of the camshaft gear to lubricate the
vacuum pump. The pump is connected to the EGR
modulator valve via a pipe and hose.
EGR Valve
1. Vacuum connection
2. Spring
3. Diaphragm
4. Housing
5. Air inlet connection
6. EGR pipe connection
7. Seal
8. Rod
The EGR valve is located on the forward end of the
intake manifold. The valve is sealed to the manifold
with an O-ring and secured with four bolts. The EGR
valve comprises a diaphragm, housing and valve.
The EGR valve is mounted on an aluminium housing
which also provides for the connection of the air intake
hose from the intercooler. The valve is positioned
opposite the exhaust gas pipe intake connection. The
valve is connected to the diaphragm by a rod and is
held in the closed position by a spring.