|
Focus |
The Engine Management
System
Here is a description of Ford 1.3ltr Endura-E engine management system
as fitted to the Ford Ka and Fiesta. There are variations on this and
other Ford engine management system now in use but it would be too
difficult to describe the operation of each and every system.
The engine management system of the 1.3 ltr Endura-E engine comprises a powertrain control module
(PCM), various sensors and actuators. The sensors send signals to
the PCM relating to engine operating conditions and the actuators react to
signals from the PCM. "These output signals are based on the evaluated input signals which are compared with calibrated data tables or maps before the output signal is
generated".
To meet 96 EEC emission regulations the engine is fitted with a catalytic converter and an evaporative emission fuel vapour
system.
Powertrain Control Module (PCM)
The PCM is either EEC IV or EEC V.
Throttle Position Sensor (TPS)
The throttle position sensor is a potentiometer which operated by the throttle plate. The throttle position sensor is supplied with a
5 volt reference voltage by the PCM. When the throttle plate is opened, a sliding contact moves over a resistance track, changing the output voltage. The output voltage is assigned to a corresponding throttle plate position by the powertrain control module.
Idle Air Control Valve (ISCV)
The idle air control valve is an electronically controlled solenoid valve which allows a flow of air to bypass the throttle plate. Engine idle speed can therefore be maintained irrespective of engine load. The idle air control valve is controlled by grounding pulses from the powertrain control module. The length of the pulse determines the position of the valve.
Camshaft Position Sensor (CMP)
The CMP scans a reference cam on the camshaft. The CMP sends an alternating voltage signal to
the PCM. This indicates the firing position of No1 cylinder. This is only
used when starting starting. after that the (PIP) signal takes over to
control the injectors.
Crankshaft Position Sensor (CKP)
The CKP sensor is also an inductive pulse generator, like the CMP which scans 36 minus 1 cast protrusions on the flywheel. Minus one means that one of the protrusions is missing. This missing protrusion is located at 90º before top dead
center and is used by the powertrain control module as a reference mark for the crankshaft position. The crankshaft position sensor sends an alternating voltage signal to the powertrain control module, which is used to determine engine speed and ignition timing.
Mass Air Flow Sensor (MAF)
The MAF sensor measures the mass of air passing through the inlet system, the measurement being based on the constant temperature hot wire principle.
A hot wire probe and an air temperature probe are used to determine the
flow of air. The PCM keeps the hot wire is always 200º C hotter than the air temperature
wire. The hot wire is cooled by the air flow and the PCM changes the heating current to maintain the 200º C temperature difference. The change in the heating current is measured as a voltage drop across a precision resistor and is assigned to a corresponding mass air flow calculation by the powertrain control module.
Engine Coolant Temperature Sensor (ECT)
The ECT sensor is a temperature dependant resister which has a negative temperature coefficient, i.e., its temperature changes inversely with respect to engine coolant temperature. The engine coolant temperature sensor is supplied with a reference voltage by the powertrain control module. When the engine coolant temperature changes, the resistance of the sensor changes thus changing the output voltage. The output voltage is assigned to a corresponding engine coolant temperature by the powertrain control module.
Intake Air Temperature Sensor (ACT or IAT)
The intake air temperature sensor is a temperature dependant resistor which has a negative temperature coefficient, i.e., its temperature changes inversely with respect to ambient temperature. The intake air temperature sensor is supplied with a reference voltage by the powertrain control module. When the intake air temperature changes, the resistance of the sensor changes thus changing the output voltage. The output voltage is assigned to a corresponding intake air temperature by the powertrain control module.
Heated Oxygen Sensor (HEGO)
The HEGO sensor is a voltage generator which is installed upstream from the catalytic converter. When the air/fuel ratio is
perfect (theoretically 14.7:1) or Lambda 1, a voltage signal of 450 mV is sent to the powertrain control module. When the mixture is lean, the voltage is reduced to 200 mV and the powertrain control module sets the air/fuel mixture towards rich. When the mixture is rich, the voltage signal is increased to 800m V and the powertrain control module sets the air/fuel mixture to lean. This provides control of exhaust emissions. To ensure the heated oxygen sensor quickly reaches its operating temperature of 300º C, it is equipped with a heating element which operates when the ignition is switched on.
The HEGO voltage should switch constantly between .2 volts and .9 volts in
a steady pattern.
Temperature and Manifold Absolute Pressure Sensor (TMAP)
The TMAP sensor fits directly into the inlet manifold and accurately measures
the vacuum from the engine. The TMAP sensor consists of a temperature sensor and a
pressure transducer and therefore replaces the IAT and the MAP sensors. The TMAP sensor provides the powertrain control module with information relating to inlet manifold vacuum and barometric pressure along with the temperature of the air
in the inlet manifold. With the ignition on but without the engine running the sensor reads barometric pressure and when the engine is running, the sensor reads inlet manifold vacuum.
Evaporative Emission System
The evaporative emission fuel vapour management system is controlled by the powertrain control module according to calibrated data tables. The function of the system is to reduce hydro-carbon emissions from the fuel tank.
The evaporative emission fuel vapour management system comprises a carbon canister and a purge
valve. When the purge valve is closed, the fuel tank is vented into the carbon canister which absorbs the fuel vapour and prevents the release of hydro-carbons into the atmosphere. When the purge valve is activated, the carbon canister is exposed to inlet manifold vacuum and the fuel vapour deposits are drawn into the inlet manifold where they mix with the incoming air/fuel charge.
|
