PGM-FI Control System: Notes

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 from fuse No. 18 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 fuse No. 33 and 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 main relay, supplying current to the fuel pump for two seconds to pressurize the fuel system. When the engine is running, the ECM supplies ground to the main relay, supplying current to the fuel pump. When the engine is not running and the ignition is on, the ECM cuts ground to the 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 below 4800 RPM. Intake air flows through a smaller chamber for higher torque. At speeds higher 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.

For component locations, see Fig 2 -Fig 7 . For circuit schematic, see Fig 8 -Fig 22 .