PGM-FI Control System: Notes

NOTE: Components are grouped into two categories. The first category covers input devices, which control or produce voltage signals monitored by the ECM. See INPUT DEVICES . The second category covers output signals, which are components controlled by the ECM. See OUTPUT SIGNALS .

The Programmed Fuel Injection (PGM-FI) system controls the engine emission and performance functions as well as providing information to other vehicle systems. With the ignition switch in RUN or START, battery voltage is supplied to the Engine Control Module (ECM) through the PGM-FI main relay and the Yellow/Black wires.

Battery voltage is supplied at all times from the White/Yellow wires to the ECM for memory functions. The ECM is grounded through the Black wires to ground G101.

The ECM is self-diagnosing and monitors the sensors for irregular signals. The ECM is programmed with settings for fuel injector discharge duration at various engine speeds and manifold pressures. Discharge duration is modified by signals sent from various sensors to determine final discharge duration. If the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator is charging, the ECM sends signal to the drive by wire system to maintain correct idle speed. The ECM is programmed with settings for basic ignition timing at various engine speeds and manifold pressures. Ignition timing is also adjusted for coolant temperature. A knock control system retards ignition timing when the knock sensor detects detonation.

For PGM-FI inputs and outputs, see Fig 1 . The PGM-FI also features the following:

Starting Control

The ECM enriches the mixture by increasing fuel injection duration when the engine is started.

Fuel Pump Control

When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay, supplying current through the fuel pump resistor to the fuel pump for two seconds to pressurize the fuel system. When the engine is running, the ECM supplies ground to the PGM-FI main relay and fuel pump relay, supplying current to the fuel pump. When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay, cutting current to the fuel pump. Engine performance is enhanced by controlling fuel pump discharge volume.

Fuel Cutoff Control

During deceleration with the throttle valve closed, current to the injectors is cut off at speeds over 1500 RPM to improve fuel economy. Fuel cutoff action also takes place when engine speed exceeds 8300 RPM to protect the engine from over-revving, regardless of the position of the throttle valve.

A/C Compressor Clutch Relay

When a demand for cooling from the air conditioning system (compressor control unit) is received, the ECM delays the compressor from being energized to enrich the fuel mixture and assure smooth transition to the A/C mode.

EVAP Purge Cut-Off Solenoid Valve

When the coolant temperature is below 153°F (67°C), the ECM supplies a ground to the EVAP purge cutoff solenoid valve which cuts vacuum to the purge control diaphragm valve.

Intake Air Bypass Control Solenoid Valve (IAB)

The IAB is activated by a signal from the ECM when the engine RPM is less than 4800 RPM. Intake air flows through a smaller chamber for higher torque. When the engine RPM is more than 4800 RPM, the ECM deactivates both solenoid valves. Intake air flows through the enlarged chamber and increases airflow.

EGR Control Solenoid Valve

When the EGR is required for control of NO_x emissions, the ECM supplies ground to the EGR control solenoid valve, supplying regulated vacuum to the EGR valve.

Fail-Safe Function

When a sensor signal abnormality occurs, the ECM ignores the signal and assumes a pre-programmed value that allows the engine to continue to run.

Back-Up Function

When an abnormality occurs in the ECM itself, a backup circuit independent of the ECM controls the injectors to permit minimal driving.