Contents: Launch mode ↧ Excess fuel removal mode ↧ Working mode ↧ Open circuit ↧ Closed loop ↧ Acceleration mode ↧ Slow-motion mode ↧ Battery voltage correction mode ↧ Fuel Shut-Off Mode ↧
Launch mode
When the ignition is turned on, the ECM energizes the fuel pump relay for 2 seconds. The fuel pump creates fuel pressure. The ECM monitors the coolant temperature (ECT) sensor and the throttle position (TP) sensor and determines the appropriate air/fuel ratio to start the engine. These ranges are 1.5 to 1 at -36C coolant temperature and 14.7 to 1 at 94C coolant temperature.
The ECM controls the amount of fuel delivered by the injector using pulses with a constant repetition rate and adjustable duration. The amount of fuel passed by the injector into the cylinder is proportional to the duration of the control pulses.
Excess fuel removal mode
If the engine floods with fuel, it can be cleared by depressing the accelerator pedal to its full stroke. The ECM will cut off fuel completely by cutting off the signal to the fuel injectors. The ECM maintains this injection mode for the entire duration of the wide-open throttle, at engine speeds below 400 rpm. If the throttle is released to a position corresponding to approximately 80% of the stroke, the ECM returns to the cranking mode.
Working mode
The operating mode has two types - "closed loop" and "open loop".
Open circuit
During initial engine start-up at cranking speeds above 400 rpm, the system goes into "open loop" mode. In "open loop", the ECM ignores the oxygen sensor signal and calculates the air/fuel ratio based on the input signals from the ECT sensor and the MAP sensor. The sensor remains in "open loop" until the following conditions are met:
- the oxygen sensor provides variable output signal data, which is an indication that it has warmed up enough for normal operation;
- eCT sensor readings are higher than the specified temperature;
- a certain period of time has passed since the engine was started.
Closed loop
The specific values for these parameters vary depending on the engine model and are stored in an electrically erasable programmable ROM (EEPROM). Once these parameters are reached, the system switches to "closed loop" mode.
In "closed loop" mode, the ECM calculates the air/fuel ratio (fuel injector on) based on the oxygen sensor signal. Thus, the air/fuel ratio remains within the range of 14.7 to 1.
Acceleration mode
The ECM detects rapid changes in throttle position and air flow and delivers additional fuel.
Slow-motion mode
The ECM detects rapid changes in throttle position and air flow and reduces fuel delivery. During very rapid deceleration, the ECM may cut off fuel delivery for a short period of time.
Battery voltage correction mode
When the battery voltage is low, the ECM can compensate for the weak spark from the ignition module in the following ways:
- increasing the injector pulse width.
- increase idle speed.
- increasing the ignition timing.
Fuel Shut-Off Mode
Fuel is not supplied by the injectors when the ignition is off. This prevents the engine from running after the ignition is off. Also, fuel is not supplied in the absence of reference pulses from the central power source. This makes it possible to prevent the engine from overfilling with fuel.
The material was created based on information from the website «CHEVYMAN»