Except California Models

PURPOSE
The multiport fuel injection computer (ECM) controls all engine operations to ensure maximum power and economy while maintaining the lowest possible level of emissions.

OPERATION

Except California Models:

Multiport Fuel Injection System (Federal):

This engine is equipped with a TOYOTA Computer Controlled System (TCCS) which centrally controls the multiport fuel injection (MFI), electronic spark advance (ESA), idle air control (IAC) and diagnosis systems etc. by means of an ECM (formerly MFI computer) employing a microcomputer.
The ECM controls the following functions:

1. Multiport Fuel Injection (MFI)
The ECM receives signals from various sensors indicating changing engine operating conditions such as:
^ Manifold absolute pressure (MAP)
^ Intake air temperature (IAT)
^ Engine coolant temperature (ECT)
^ Engine speed (RPM)
^ Throttle valve opening angle (TP)
^ Exhaust oxygen content etc. (O2S)
The signals are utilized by the ECM to determine the injection duration and timing necessary for an optimum air-fuel ratio to produce the best balance of power, economy and low emissions.

2. Electronic Spark Advance (ESA)
The ECM is programmed with data for optimum ignition timing under all operating conditions. Using data provided by sensors which monitor various engine functions (engine speed (RPM), engine coolant temperature (ECT), etc.), the microcomputer (ECM) triggers the spark at precisely the right instant.

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

4. Diagnosis
The ECM detects any malfunctions and abnormalties in the sensor network and lights a "Check" engine light (MIL) on the combination meter. At the same time, trouble is identified and a diagnostic trouble code is recorded by the ECM. The diagnostic trouble code can be read by the number of blinks of the "Check" engine light (MIL) when terminals TE1 and E1 of DLC1 are connected. The diagnostic trouble codes are described under On-Board Diagnostic System.

5. Self-Correction Function
If any sensor malfunctions, an average value recorded in the back-up circuit is substituted to make driving possible. If danger is predicted, the engine is stopped and the "Check" engine light (MIL) will light up.

6. Fail-Safe Function
In the event of the sensor malfunction, a back-up circuit will take over to provide minimal driveability, and the "Check" engine light (MIL) will illuminate.