SFI
3
DESCRIPTION AND OPERATION
ENGINE MANAGEMENT SYSTEM
Description
The engine management system (EMS) maintains
optimum engine performance over the entire
operating range. The correct amount of fuel is
metered into each cylinder inlet tract and the ignition
timing is adjusted at each spark plug.
The system is controlled by the Engine Control
Module (ECM) which receives data from sensors
located on and around the engine. From this
information it provides the correct fuel requirements
and ignition timing to suit all engine loads and speeds.
The fuel injection system uses a hot wire Mass Air
Flow sensor to calculate the amount of air flowing into
the engine.
The ignition system does not use a distributor. It is a
direct ignition system (DIS), using four double ended
coils. The circuit to each coil is completed by
switching inside the ECM.
The on board diagnostic system detects any faults
which may occur within the EMS. Fault diagnosis
includes failure of all EMS sensors and actuators,
emissions related items, fuel supply and exhaust
systems.
The system incorporates certain default strategies to
enable the vehicle to be driven in case of sensor
failure. This may mean that a fault is not detected by
the driver. The fault is indicated by illumination of the
malfunction indicator light (MIL).
Crankshaft position (CKP) sensor
The crankshaft position sensor is the most important
sensor on the engine. It is located in the left hand side
of the torque convertor housing. The signal it
produces informs the ECM:
- that the engine is turning
- how fast the engine is turning
- at which stage the engine is, in the combustion
cycle.
As there is no default strategy, failure of the
crankshaft sensor will result in the engine failing to
start. The fault is indicated by illumination of the
malfunction indicator light (MIL).
Camshaft position (CMP) sensor
The camshaft position sensor is located in the engine
front cover. It produces four pulses every two
revolutions. The signals are used in two areas,
injector timing corrections for fully sequential fuelling
and active knock control.
If the camshaft sensor fails, default operation is to
continue normal ignition timing. The fuel injectors will
be actuated sequentially, timing the injection with
respect to top dead centre. Injection will either be
correct or one revolution out of synchronisation. The
fault is not easily detected by the driver. Sensor failure
will be indicated by illumination of the malfunction
indicator light (MIL).
Mass air flow (MAF) sensor
The ’hot wire’ type mass air flow sensor is mounted
rigidly to the air filter and connected by flexible hose to
the plenum chamber inlet. The sensing element of the
MAF Sensor is a wire which is heated. Air flows
across the heated wire cooling it and thus changing its
resistance. The ECM measures this change in
resistance, and together with intake air temperture
sensor resistance, calculates the amount of air flowing
into the engine.
As there is no default strategy, failure will result in the
engine starting, and dying when it reaches 550
rev/min, when the ECM detects no MAF Sensor
signal. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
Throttle position (TP) sensor
The throttle position sensor is mounted on the plenum
chamber and connected directly to the throttle shaft.
The sensor is a variable resistor, the signal from
which (0 - 5V) informs the ECM of the actual position
of the throttle disc. As there is no default strategy,
failure of the sensor will result in poor idle and lack of
throttle response. If failure occurs in the closed
position the engine will only reach 1750 rev/min when
the ECM will initiate overrun fuel cut off. The fault is
indicated by illumination of the malfunction indicator
light (MIL).