Powertrain Management: Description and Operation

GENERAL INFORMATION
The Multiport Fuel Injection System consists of sensors which detect the engine conditions, the Powertrain Control Module (PCM) which controls the system based on signals from these sensors, and actuators which operate under the control of the PCM.

The PCM carries out activities such as fuel injection control, idle air control and ignition timing control.

In addition, the PCM is equipped with several diagnostic test modes which simplify troubleshooting when a problem develops.

FUEL INJECTION CONTROL
The injector drive times and injector timing are controlled so that the optimum air/fuel mixture is supplied to the engine to correspond to the continually-changing engine operation conditions.

A single injector is mounted at the intake port of each cylinder. Fuel is sent under pressure from the fuel tank by the fuel pump, with the pressure regulated by the fuel pressure regulator. The regulated fuel is distributed to each of the injectors.

Fuel injection is normally carried out once for each cylinder for every two rotations of the crankshaft. The firing order is 1-3-4-2. This is called multiport. The PCM provides a richer air/fuel mixture by carrying out "open-loop" control when the engine is cold or operating under high load conditions in order to maintain engine performance.

In addition, when the engine is warm or operating under normal conditions, the PCM maintains the optimum the air/fuel mixture for 3-way catalyst performance by using the oxygen sensor input.

IDLE AIR CONTROL
The idle speed is kept at the optimum speed by controlling the amount of air that bypasses the throttle valve in accordance with changes in idling conditions and engine load during idling.

The PCM drives the idle air control (IAC) motor to keep the engine running at the pre-set idle target speed in accordance with the engine coolant temperature and air conditioning load. In addition, when the air conditioning switch is turned off and on while the engine is idling, the IAC motor operates to adjust the throttle valve bypass air amount in accordance with the engine load conditions in order to avoid fluctuations in the engine speed.

IGNITION TIMING CONTROL
The ignition power transistor is built into the PCM. It turns the ignition primary circuit on and off to respectively supply and cut off primary current flow to the ignition coil.

This controls the ignition timing in order to provide the optimum ignition timing with respect to the engine operating conditions. The ignition timing is determined by the PCM from the engine speed, intake air volume, engine coolant temperature and atmospheric pressure.