Fuel Injector: Description and Operation
Fuel Injectors
The Fuel Injectors are electronically controlled solenoid valves that provide precise metered and atomized fuel into the engine intake ports.
Fuel is supplied from the fuel rail to the injector body. The fuel is channeled through the injector body to the needle valve and seat at the tip of the injector. Without electrical current, the needle valve is sprung closed against the seat.
The Fuel Injectors receive voltage from the Main Relay. The EMS2000 activates current flow through the injector solenoid creating a magnetic field that pulls the needle "up" off of its seat. The pressurized fuel flows through the tip of the injector that is fitted with a directional angle "plate" with dual outlets. This "fans out" the spray into an angled patterns which helps to atomize the fuel. When the EMS2000 removes the ground, the needle valve is sprung closed against the seat and fuel flow through the injector is stopped. The lower portion of the injector body is jacketed in metal.
The length of time that the EMS2000 activates the Fuel Injectors is very brief, the duration is in milli-seconds (ms). This affects the amount of fuel volume flowing through the Fuel Injectors. The EMS2000 will vary the length of time (ms) to regulate the air/fuel ratio (mixture).
There are two types of injectors used on the MINI. MINI COOPER uses an injector with 4 holes, while MINI COOPER S uses an injector with a higher flow rate having 2 holes.
Injectors for both models are 62 mm in length and operate on a fuel pressure of 3.5 Bar. The electrical connectors are different for each type of injector preventing accidental installation of the wrong injector.
Injector "ON" Time
Injector "ON" Time is the length of time in ms the injector is active and flowing fuel. The injection ms value will be regulated based on among other things battery voltage. When cranking, the voltage is low and the EMS2000 will increase the ms value to compensate for injector "lag time". When the engine is running and the battery voltage is higher, the EMS2000 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 EMS2000 based on the Engine Coolant Temperature Sensor input during start up.
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 EMS2000 to adjust the injection ms value to compensate during warm up and minimize the injected fuel at normal engine operating temperature.
When the engine is at idle, minimum injection is required. Additional fuel will be added if the EMS observes low engine rpm and increasing throttle/air volume inputs (acceleration enrichment). As the throttle is opened, the EMS2000 recognizes acceleration and rate of movement. The EMS2000 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 EMS2000 will add more fuel (full load enrichment).
As the throttle is closed, the EMS2000 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 EMS2000 uses input from the TMap (and Map if COOPER S), the Engine Coolant Temperature Sensor and throttle position to calculate the volume of air consumed by the engine. This calculated measurement is used by the EMS2000 to determine the amount of fuel to be injected to "balance" the air/fuel ratio.
The Crankshaft Position/RPM signals the EMS2000 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 EMS2000 will not activate the injectors.
The Camshaft Position (Cylinder ID) affects the injection timing (Semi-Sequential/Full Sequential). To accomplish this, the EMS2000 contains four Final Stage output transistors that activate the injectors individually. The engine operates sufficiently on Semi-Sequential Injection (two groups of two), but more efficiently on Full Sequential Injection (four individual). If one of the fuel injector circuits is faulted, the engine can still operate on limited power from the remaining fuel injector circuits.
Injection "Reduction" Time
Reduction Time is required to control fuel economy, emissions, engine and vehicle speed limitation. The EMS2000 will "trim" back or deactivate the fuel injection as necessary while maintaining optimum engine operation.
As the throttle is closed during deceleration, the EMS2000 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 EMS2000 will selectively deactivate injectors to control maximum engine rpm (regardless of vehicle speed). When the engine speed reaches 6500 rpm, the injectors will be individually deactivated as required 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 also limited by the EMS2000 selectively deactivating the injectors (regardless of engine rpm). This limitation is based on the vehicle dimensions, specifications and installed tires (speed rating).
The EMS2000 will also protect the Catalytic Converter by deactivating the injectors. If the EMS2000 detects a "misfire" (ignition, injection or combustion) it can selectively deactivate the Final Stage output transistor for that cylinder(s).
The injector(s) will not open, preventing unburned fuel from entering the exhaust system. On the EMS2000 system, there are four individual injector circuits resulting in deactivation of one or multiples. This will limit engine power, but protect the Catalytic Converter.
Fuel Injection Control Monitoring is performed by the EMS2000 for OBD II requirements. Faults with the fuel injectors and/or control circuits will be stored in memory. This monitoring includes:
- Closed Loop Operation
- Oxygen Sensor Feedback
These additional corrections are factored into the calculated injection time. If the correction factor exceeds set limits a fault will be stored in memory. When the criteria for OBD II monitoring is achieved, the "Malfunction Indicator Light" will be illuminated.
Function
The fuel injector valves have a small solenoid coil that ensures fine atomization during fuel injection. The engine control module sends a signal to the fuel injector valve to activate the solenoid coil, raising the needle from the valve base. The fuel is injected in the intake pipe. The quantity of injected fuel is controlled by means of a PWM signal.
Installation location
The fuel injector valves are located on the intake pipe.
Failure
If one or more fuel injector valves should fail, the following symptoms occur: poor running characteristics; misfiring; the engine does not start. The MIL lights up.