Fuel And Emissions System Description - PGM-FI System
Fuel and Emissions System Description - PGM-FI System
PGM-FI System
The programmed fuel injection (PGM-FI) system is a sequential multiport fuel injection system.
Alternator Control
The alternator signals the ECM during charging. The ECM then controls the voltage generated at the alternator according to the electrical load determined by the electrical load detector (ELD) and the driving mode. This reduces engine load to improve fuel economy.
Air Conditioning (A/C) Compressor Clutch Relay
When the ECM receives a demand for cooling from the A/C system, it delays the compressor from being energized, and enriches the mixture to assure a smooth transition to the A/C mode.
Air Fuel Ratio (A/F) Sensor
The A/F sensor operates over a wide air/fuel range. The A/F sensor is installed upstream of the TWC, and sends signals to the ECM which varies the duration of fuel injection accordingly.
Barometric Pressure (BARO) Sensor
The BARO sensor is inside the ECM. It converts atmospheric pressure into a voltage signal that is used by the ECM to modify the basic duration of the fuel injection discharge.
Camshaft Position (CMP) Sensor B
CMP sensor B detects the position of the No. 1 cylinder as a reference for sequential fuel injection to each cylinder.
Crankshaft Position (CKP) Sensor
The CKP sensor detects crankshaft speed and is used by the ECM to determine ignition timing and timing for fuel injection of each cylinder, and engine misfire detection.
Engine Coolant Temperature (ECT) Sensors 1 and 2
ECT sensors 1 and 2 are temperature dependent resistors (thermistors). The resistance decreases as the engine coolant temperature increases.
Ignition Timing Control
The ECM contains the memory for basic ignition timing at various engine speeds and manifold absolute pressures. It also adjusts the timing according to engine coolant temperature and intake air temperature.
Injector Timing and Duration
The ECM contains the memory for basic discharge duration at various engine speeds and manifold absolute 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 ECM detects long term malfunctions in the fuel system and sets diagnostic trouble codes (DTCs) if needed.
Knock Sensor
The knock control system adjusts the ignition timing to minimize knock.
Malfunction Indicator Lamp (MIL) Indication (In relation to Readiness Codes)
The vehicle has certain readiness codes that are part of the on-board diagnostics for the emissions systems. If the vehicle's battery has been disconnected or gone dead, if the DTCs have been cleared, or if the ECM has been reset, these codes are reset. In some states, part of the emissions testing is to make sure these codes are set to complete. If all of them are not set to complete, the vehicle may fail the test, or the test cannot be finished.
To check if the readiness codes are set to complete, turn the ignition switch to ON (II), but do not start the engine. The MIL will come on for 15-20 seconds. If it then goes off, the readiness codes are complete. If it flashes five times, one or more readiness codes are not complete. To set each code, drive the vehicle or run the engine as described in the procedures Monitors, Trips, Drive Cycles and Readiness Codes.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor converts manifold absolute pressure into electrical signals that are sent to the ECM.
Mass Air Flow (MAF) Sensor/Intake Air Temperature (IAT) Sensor
The mass air flow (MAF) sensor/intake air temperature (IAT) sensor contains a hot wire sensor, a cold wire sensor, and a thermistor. It is in the intake air passage. The resistance of the hot wire sensor, the cold wire sensor, and the thermistor changes due to intake air temperature and air flow. The control circuit in the MAF sensor controls the current to keep the hot wire at a set temperature. The current is converted to voltage in the control circuit, then output to the ECM.
Output Shaft (Countershaft) Speed Sensor
This sensor detects countershaft speed.
Secondary Heated Oxygen Sensor (Secondary HO2S)
The secondary HO2S detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC), and sends signals to the ECM. To stabilize its output, the sensor has an internal heater. The ECM compares the HO2S output with the A/F sensor output to determine catalyst efficiency. The secondary HO2S is on the TWC.
