Powertrain Management: Description and Operation

PURPOSE/OPERATION

Fuel Injector Timing and Duration
The PGM-FI system on this model is a sequential multiport fuel injection system. The engine control module contains memories for the basic discharge durations at various engine speeds and manifold pressures. The basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.

Idle Air Control
The system is equipped with an Idle Air Control Valve. When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator is charging, the engine control module controls current to the idle air control valve to maintain correct idle speed.

Ignition Timing Control
The engine control module contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing is also adjusted for engine coolant temperature.
A Knock Control System is also used. When detonation is detected by the knock sensors, the ignition timing is retarded.

Other Control Functions

Starting Control
When the engine is started, the engine control module provides a rich mixture by increasing fuel injector duration.

Fuel Pump Control
When the ignition switch is initially turned on, the FCM supplies ground to the PGM-FI main relay that supplies current to the fuel pump for two seconds to pressurize the fuel system.
When the engine is running, the engine control module supplies ground to the PGM-FI main relay that supplies current to the fuel pump.
When the engine is not running and the ignition is on, the engine control module cuts ground to the PGM-FI main relay which cuts current to the fuel pump.

Fuel Cut-off Control
During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at speeds over 980 rpm (M/T) or 980 rpm (A/T).
Fuel cut-off action also takes place when engine speed exceeds, 7,100 rpm, regardless of the position of the throttle valve, to protect the engine from over-revving.
Fuel cut-off action also takes place when vehicle speed exceeds, 131 mph (210 km/h).

A/C Compressor Clutch Relay
When the engine control module receives a demand for cooling from the air conditioning system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.

Evaporative Emission (EVAP) Purge Control Solenoid Valve
When the engine coolant temperature is below 1 58°F (70°C), the engine control module supplies a ground to the EVAP purge control solenoid valve which cuts vacuum to the EVAP purge control diaphragm valve.

Intake Air Bypass Control Solenoid Valve
When the engine rpm is below 4,900 rpm, the intake air bypass control solenoid valve is activated by a signal from the engine control module, intake air flows through the long intake path, then high torque is delivered. At speeds higher than 4,900 rpm, the solenoid valve is deactivated by the engine control module, and intake air flows through the short intake path in order to reduce the resistance in airflow.

Exhaust Gas Recirculation (EGR) Control Solenoid Valve
When the EGR is required for control of oxides of nitrogen (NOx) emissions, the engine control module supplies ground to the EGR control solenoid valve which supplies regulated vacuum to the EGR valve.

Alternator (ALT) Control
The system controls the voltage generated at the alternator in accordance with the electrical load and drive mode, and reduces the engine load to improve the fuel economy.

Engine Control Module Fail-safe/Back-up Functions

Fail-Safe Function
When an abnormality occurs in a signal from a sensor, the engine control module ignores that signal and assumes a pro-programmed value for that sensor that allows the engine to continue to run.

Back-up Function
When an abnormality occurs in the engine control module itself, the fuel injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

Self-diagnosis Function [Malfunction Indicator Lamp
When an abnormality occurs in a signal from a sensor, the engine control module lights the MIL and Stores the code in erasable memory. When the ignition is initially turned on, the engine control module supplies ground for the MIL for two seconds to check the MIL bulb condition.