Computers and Control Systems: Description and Operation
System description - PGM-FI SystemThe Programmed Fuel Injection (PGM-FI) system is a sequential multiport fuel injection system.
Fuel Injector Timing and Duration
The PCM contains the memory for basic discharge duration 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.
By monitoring Long Term Fuel Trim, the PCM detects long term malfunctions in the fuel system, and will set a DTC if the malfunction occurs during two consecutive trips.
Ignition Timing Control
The PCM contains the memory for basic ignition timing at various engine speeds and manifold air flow rates. It also adjusts the timing according to engine coolant temperature. The PCM detects misfiring by using the CKP sensor to monitor fluctuations in crankshaft speed. It will then set DTCs depending on how much misfiring occurs.
Starting Control
When the engine is started, the PCM provides a rich mixture by increasing fuel injector duration.
Alternator Control
The alternator signals the PCM during charging. The PCM then controls the voltage generated at the alternator according to the electrical load determined by the ELD (Electrical Load Detector) and driving mode. This reduces engine load to improve fuel economy.
A/C Switch
The A/C (air conditioning) switch signals the PCM whenever there is a demand for cooling.
A/C Compressor Clutch Relay
When the PCM receives a demand for cooling from the A/C system, it delays the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.
TDC (Top Dead Center) Sensors
The TDC1/2 sensor determines ignition timing at start up (cranking) and when crank angle is abnormal.
CKP (Cylinder Position) Sensor
The CKP sensor determines timing for fuel injection of each cylinder and also detects engine speed.
MAP (Manifold Absolute Pressure) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals to the PCM.
IAT (Intake Air Temperature) Sensor
The IAT sensor is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the intake air temperature increases.
ECT (Engine Coolant Temperature) Sensor
The ECT sensor is a temperature dependent resistor (thermistor). The resistor of the thermistor decreases as the Engine Coolant temperature increases.
TP (Throttle Position) Sensor
The TP sensor is a potentiometer connected to the throttle valve shaft. As the throttle position changes, the sensor varies the signal voltage to the PCM. The TP sensor is not replaceable apart from the throttle body.
Baro (Barometric Pressure) Sensor
The barometric pressure sensor is inside the PCM. It converts atmospheric pressure into a voltage signal that modifies the basic duration of the fuel injection discharge.
Primary and Secondary HO2S (Heated Oxygen sensors)
The heated oxygen sensors detect the oxygen content in the exhaust gas, then sends signals to the PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensors have an internal heater. The primary sensor is installed in the exhaust pipe. The secondary sensor is installed in the TWC.
By controlling the air/fuel ratio with sensors, the deterioration of the primary sensor can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the PCM sets a DTC.
Knock Sensor
The knock control system adjusts the ignition timing for the octane rating of the gasoline used.
ECM/PCM FAIL-SAFE/BACK-UP FUNCTIONS
Electronic Control System
The functions of the fuel and emission control Systems are managed by the powertrain control module (PCM).
Fail-safe Function
When an abnormality occurs in a signal from a sensor, the PCM ignores that signal and assumes a pre-programmed value for that sensor that allows the engine to continue to run.
Back-up Function
When an abnormality occurs in the PCM, the fuel injectors are controlled by a back-up circuit independent of the system to permit minimal driving.
Self-diagnosis
When an abnormality occurs in the signal from a sensor, the PCM supplies ground for the Malfunction Indicator Lamp (MIL) and stores the Diagnostic Trouble Code (DTC) in erasable memory. When the ignition is first turned on, the ECM/PCM supplies ground for the MIL for two seconds to check the MIL bulb condition.
Two Driving Cycle Detection Method
To prevent false indications, the "two driving cycle detection method" is used for the HO2S, fuel metering-related, idle control system, ECT sensor, EGR system, TWC, EVAP control system and other self-diagnostic functions. When an abnormality occurs, the PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the PCM informs the driver by turning on the MIL.