Principle Of Operation

Fuel Management delivers fuel from the tank to the intake ports of the engine. To accomplish this, fuel supply  must be available to the fuel injectors. Then the fuel must be injected  in the precise amount and at the correct time. The ECM does not directly monitor fuel supply, although it does control fuel supply. The Fuel Pump  supplies fuel when it receives operating voltage from the Engine Control Module Relay supplying the Fuel Pump Relay. The ECM controls and monitors fuel injection. 

The Fuel Pump  will be activated when the ignition (KL15) is switched "on" and the ECM supplies a ground circuit to activate the Fuel Pump Relay. The Fuel Pump Relay supplies operating power to the in-tank mounted fuel pump. This is a momentary activation to "pressurize" (prime) the fuel system.

The ECM then requires an engine RPM signal from the Crankshaft Position/RPM Sensor to maintain continuous Fuel Pump Relay activation.

If the engine RPM signal is not present, the ECM will deactivate the Fuel Pump Relay.

The Fuel Injectors  will be opened by the ECM to inject pressurized fuel into the intake ports. The Fuel Injectors receive voltage from the Engine Control Module Relay. The ECM controls the opening by activating the ground circuit for the Solenoid Windings. The ECM will vary the duration (in milli-seconds) of "opening" time to regulate the air/fuel ratio.

The ECM has two Final Stage output transistors that switch ground to the four injector solenoids. The Injector "triggering" is first established from the Crankshaft Position/RPM Sensor.

The ECM is programmed to activate the Final Stage output transistors once for every revolution of the crankshaft (Parallel Injection). The ECM calculates the total milli-second time to open the injectors and cuts that value in half.

The injectors are all opened at the same time (in parallel) for every complete crankshaft revolution. This delivers half of the fuel charge at each injection so that the engine receives the full fuel charge during a complete working cycle. This process enhances fuel atomization during start up.

During start up, the ECM recognizes the Camshaft Position (Cylinder ID) input. It then switches the injection to Semi-Sequential. This process "times" the injection closer to the intake valve opening for increased efficiency.

When activated, each group (grouped in pairs) delivers the full fuel charge at separate times for each engine working cycle.

The Camshaft Position input is only checked by the ECM during start up. The camshaft position is referenced to the crankshaft position, and is not monitored until the next engine start up. Therefore, if this input is lost when the engine is already running, there will be no effect. There will only be an effect if this input is missing when the engine is started. For this condition, the ECM will continue operating the injectors in Parallel.

The Injector "open" Time  to maintain engine operation after it has been started is determined by the ECM (programming). The ECM will calculate the engine "load" based on a combination of the following inputs:

• Battery Voltage 
• Throttle Position 
• Air Flow Volume 
• Air Temperature 
• Crankshaft Position/RPM 
• Crankshaft Position (Cylinder ID) 
• Engine Coolant 
• Oxygen Sensor (Detail in Emissions) 

The injection ms value will be regulated based on battery voltage. When cranking, the voltage is low and the ECM will increase the ms value to compensate for injector "lag time". When the engine is running and the battery voltage is higher, the ECM will decrease the injection ms value due to faster injector reaction time.

Cold starting requires additional fuel to compensate for poor mixture and the loss of fuel as it condenses onto cold intake ports, valves and cylinder walls. The cold start fuel quantity is determined by the ECM based on the Engine Coolant Temperature Sensor input during start up.

During cranking, additional fuel is injected (in Parallel) for the first few crankshaft revolutions. After the first few crankshaft revolutions, the injected quantity is metered down as the engine comes up to speed. When the engine speed approaches idle RPM, the ECM recognizes the Camshaft Position and switches to Semi-Sequential injection.

When the engine is cold, optimum fuel metering is not possible due to poor air/fuel mixing and an enriched mixture is required. The Coolant Temperature input allows the ECM to adjust the injection ms value to compensate during warm up and minimize the injected fuel at engine operating temperature.

When the engine is at idle, minimum injection is required. Additional fuel will be added if the ECM observes low engine RPM and increasing throttle/air volume inputs (acceleration enrichment). As the throttle is opened, the ECM monitors acceleration and rate of movement. The ECM will increase the volume of fuel injected into the engine by increasing the injection ms value. The "full throttle" position indicates maximum acceleration and the ECM will add more fuel (full load enrichment).

As the throttle is closed, the ECM decreases the injection ms value (fuel shut off) if the RPM is above idle speed (coasting). This feature decreases fuel consumption and lowers emissions. When the engine RPM approaches idle speed, the injection ms value is increased (cut-in) to prevent the engine from stalling. The cut-in RPM is dependent upon the engine temperature and the rate of deceleration.

The Air Flow Volume signal provides the measured amount of intake air volume. This input is used by the ECM to determine the amount of fuel to be injected to "balance" the air/fuel ratio.

The Air Temperature Signal allows the ECM to make a calculation of air density. The varying voltage input from the NTC sensor indicates the larger proportion of oxygen found in cold air, as compared to less oxygen found in warmer air. The ECM will adjust the amount of injected fuel because the quality of combustion depends on oxygen sensing ratio (details in Emissions).

The Crankshaft Position/RPM signals the ECM to start injection as well as providing information about the engine operation. This input is used in combination with other inputs to determine engine load which increases/decreases the injection ms value. Without this input, the ECM will not activate the injectors.

The Camshaft Position (Cylinder ID) affects the injection ms value (half= Parallel Injection or full= Semi-Sequential Injection) and the timing when it is injected to the engine. To accomplish this, the ECM contains two Final Stage output transistors that activate the injectors in two groups. The engine operates sufficiently on Parallel Injection, but more efficiently on Semi-Sequential Injection. If one of the circuits faulted, the engine can still operate on limited power from the remaining circuit.

Injection "Reduction" Time  is required to control fuel economy, emissions, engine and vehicle speed limitation. The ECM will "trim" back or deactivate the fuel injection as necessary while maintaining optimum engine operation.

As the throttle is closed during deceleration, the ECM decreases the injection ms value (fuel shut off) if the RPM is above idle speed (coasting). This feature decreases fuel consumption and lowers emissions.

When the engine RPM approaches idle speed, the injection ms value is increased (cut-in) to prevent the engine from stalling. The cut-in RPM is dependent upon the engine temperature and the rate of deceleration. This function can be observed as displayed on the Fuel Economy (MPG) gage.

The ECM will deactivate the injectors to control maximum engine RPM (regardless of vehicle speed). When the engine speed reaches 6500 RPM, the injectors will be deactivated to protect the engine from over-rev. As the engine speed drops below 6500 RPM, injector activation will be resumed. This feature does not protect the engine from a forced over-rev such as improperly downshifting a manual transmission equipped vehicle (driver error). 

Maximum vehicle speed is limited by the ECM reducing the injection ms value (regardless of engine RPM). This limitation is based on the vehicle dimensions, specifications and installed tires (speed rating).

The ECM will also protect the Catalytic Converter by deactivating the injectors.

If the ECM detects a fault in the primary ignition system, it can selectively deactivate the Final Stage output transistor for that cylinder.

The injector will not open, preventing unburned fuel from entering the exhaust system.

On the M1.7.2 system, there are two injectors per circuit resulting in deactivation of both.

This will limit engine power, but protect the Catalytic Converter.