300Tdi Discovery
Mpi
1
DESCRIPTION AND OPERATION
DESCRIPTION
The Mpi Modular Engine Management System
(MEMS) controls the fuel injection and programmed
ignition systems.
The main features are as follows:
•
The Engine Control Module (ECM) controls
programmed ignition and fuel injection. The ECM
incorporates short circuit protection and can
store intermittent faults on certain inputs.
Testbook can interrogate the ECM for these
stored faults.
•
The ECM uses the speed/density method of air
flow measurement to calculate fuel delivery. This
method measures the inlet air temperature and
inlet manifold pressure and assumes that the
engine is a calibrated vacuum pump with its
characteristics stored in the ECM
•
If certain system inputs fail, the ECM implements
a back-up facility to enable the system to
continue functioning, although at a reduced level
of performance.
•
A separate diagnostic connector allows engine
tuning or fault diagnosis to be carried out using
Testbook without disconnecting the ECM
harness connector.
•
The ECM harness multiplug incorporates
specially plated pins to minimise oxidation and
give improved reliability.
•
The throttle potentiometer requires no
adjustment in service. The following components
supply data for both fuelling and ignition:
Ignition system
The ECM determines the optimum ignition timing
based on the signals it receives from the following
sensors:
1. Crankshaft sensor - Engine speed and
crankshaft position.
2. Manifold absolute pressure sensor - Engine load
3. Coolant temperature sensor - Engine
temperature.
4. Manifold absolute pressure sensor - Throttle
closed.
5. Knock sensor - Engine noise and vibration.
MEMS uses no centrifugal or vacuum advance, timing
being controlled by the ECM which is energised by the
main relay, within the relay module. Spark distribution
is achieved by 2 coils mounted at the rear of the
engine and controlled by the ECM.
