Powertrain Management: Description and Operation

The Multiport Fuel Injection (MFI) system is composed of three basic systems: the Fuel System, the Air Induction System and the Electronic Control System which also controls the Ignition system.

FUEL SYSTEM

PURPOSE
The Fuel System supplies sufficient fuel under a constant pressure to the injectors. In accordance with signals from the Engine Control Module (ECM), the injectors inject into the intake manifold the most appropriate quantity of fuel for the engine condition.

OPERATION
Fuel, pumped by the fuel pump, flows through the fuel filter and is distributed to each injector and cold start injector at a set pressure maintained by the fuel pressure regulator. The fuel pressure regulator adjusts the pressure of the fuel from the fuel line (high pressure side) to a pressure roughly 284 kPa (41 psi) higher than the pressure inside the intake manifold. Excess fuel is returned to the fuel tank through the return pipe.

AIR INDUCTION SYSTEM

PURPOSE
The air induction system provides the correct amount of air for the engine operating condition.

OPERATION
Air filtered through the air cleaner passes through the throttle valve opening in the throttle body and into the air intake chamber. The amount of intake air pressure is monitored by the Manifold The Multiport Fuel Injection (MFI) system is composed of three basic systems: the Fuel System, the Air Induction System and the Electronic Control System which also controls the Ignition system.


ELECTRONIC CONTROL SYSTEM

PURPOSE
The Toyota Computer Controlled System (TCCS) consists of sensors which detect various engine conditions and an ECM which controls the fuel injection timing, the self diagnostic function, the ignition timing control, the idle speed control, the fuel pressure control and the fuel pump control.

OPERATION
The TCCS controls these systems in the following manner;

Multiport Fuel Injection (MFI)
The ECM receives signals from various sensors indicating changing engine operating conditions such as; intake air pressure, engine speed, intake air temperature, acceleration/deceleration, engine coolant temperature, exhaust oxygen content etc.. These signals are utilized by the ECM to determine the injection duration necessary for an optimum air-fuel ratio.

Electronic Spark Advance (ESA)
The ECM is programmed with data for optimum ignition timing under all operating conditions. Again, using data provided by sensors which monitor various changing engine conditions the ECM triggers the spark at precisely the right instant.

Idle Air Control (IAC)
The ECM is programmed with target idling speed values to respond to different engine conditions (engine coolant temperature, air conditioning ON/OFF, etc.). Sensors transmit signals to the ECM which control the flow of air through the throttle valve bypass and adjust idle speed to the target value.

Fail-Safe Function
In the event of a sensor malfunction, a backup circuit will take over to provide minimal driveability, and the Malfunction Indicator Lamp (MIL) will light up to warn the driver of the malfunction, but the diagnostic trouble code is not output.

Diagnosis Function
When the ECM detects a malfunction or abnormalities in the sensor network, it lights the MIL in the combination meter. At the same time, the trouble is identified and a Diagnostic Trouble Code (DTC) is recorded and stored by the ECM.