Range Rover P38
17
EMISSION CONTROL
NEW RANGE ROVER
4
DESCRIPTION AND OPERATION
Vacuum supplied by the EGR modulator valve acts on
the diaphragm, overcoming the spring pressure and
pulling the valve open up to 2.5 mm (0.1 in.). This
exposes the exhaust gas pipe connection and allows
gases to be drawn into the intake manifold. When the
vacuum is removed the diaphragm moves under
spring pressure, closing the valve and sealing the
EGR pipe inlet with a seal on the valve. The extent to
which the valve opens is controlled by the vacuum
level supplied from the EGR modulator, which in turn
is controlled by the ECM.
EGR Modulator valve
1. Vacuum pipe to EGR valve
2. Vacuum pipe from vacuum pump
3. Modulator valve
4. Electrical connector
5. Air filter
The EGR modulator valve is located in the engine
compartment on the left inner wing near the bulkhead.
The EGR modulator is vacuum operated through a
solenoid valve. When the ECM determines that EGR
should take place, the solenoid valve is modulated
and vacuum, supplied from the vacuum pump, opens
the EGR valve. When EGR is not required, the ECM
switches the control solenoid to close the vacuum to
the EGR valve.
The modulator valve receives full vacuum from the
pump and is also subjected to atmospheric pressure
supplied from an air filter attached to the side of the
EGR modulator valve. The vacuum and atmospheric
pressure are mixed inside the modulator valve by
electrical actuation of the solenoid creating a
controlled vacuum.
Failure of the EGR modulator valve may result in a
reduction of engine performance and the EGR may
shut down or operate at full EGR.
Mass Air Flow (MAF) Sensor
1. Electrical connector
2. Air cleaner outlet pipe
3. MAF sensor
4. Air cleaner housing
The MAF sensor, located in the air cleaner outlet pipe,
monitors the amount of air being drawn into the intake
manifold. This data is used by the ECM to calculate
the injected fuel volume, the intake air temperature
and the rate of EGR.
The MAF sensor is a hot film sensor which has a
heated surface maintained by an electrical current at a
constant temperature. With cool air flowing past the
sensor, the volume of air drawn into the intake
manifold is measured by the electrical current required
to keep the temperature of the hot film sensor
constant.
