Discovery II
EMISSION CONTROL - V8
17-2-38 DESCRIPTION AND OPERATION
Mass Air Flow (MAF) Sensor and Air Temperature Sensor
The engine management ECM uses the mass air flow sensor to measure the mass of air entering the intake and
interprets the data to determine the precise fuel quantity which needs to be injected to maintain the stoichiometric
air:fuel ratio for the exhaust catalysts. If the mass air flow sensor fails, lambda control and idle speed control will be
affected and the emission levels will not be maintained at the optimum level. If the device should fail and the ECM
detects a fault, it invokes a software backup strategy.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
The air temperature sensor is used by the engine management ECM to monitor the temperature of the inlet air. If the
device fails, catalyst monitoring will be affected. The air temperature sensor in integral to the mass air flow sensor.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
Throttle Position Sensor
If the engine management ECM detects a throttle position sensor failure, it may indicate a blocked or restricted air
intake filter. Failure symptoms may include:
l
Poor engine running and throttle response
l
Emission control failure
l
No closed loop idle speed control
l
Altitude adaption is incorrect
If a signal failure should occur, a default value is derived using data from the engine load and speed.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
Atmospheric pressure will vary with altitude and have a resulting influence on the calculations performed by the ECM
in determining the optimum engine operating conditions to minimise emissions. The following are approximate
atmospheric pressures for the corresponding altitudes:
l
0.96 bar at sea level
l
0.70 bar at 2,750 m (9,000 ft.)
