Interaction of constituent elements
The pistons that rise and fall while the engine is running draw in air. If you fully depress the accelerator pedal, then the engine sucks in as much air as possible, because in this case both throttle valves are fully open. Accordingly, when the throttle valves are closed or partially open, the amount / mass of air is less. For clean engine operation, air must be mixed with the fuel in a precisely defined proportion. The MPI injection system uses the intake air mass to determine the fuel/air ratio. The air mass meter serves as a source of information for the intake air mass for the MPI control unit. The comparable value of the MPFI injection system is exhaust manifold pressure and temperature information. The control unit can give the correct pulses to open and close the injection nozzles. A longer opening is necessary if there is a need for a large amount of fuel - a short opening is sufficient if only a small amount of fuel is needed. «Injection power» injectors remains thus constant. The reduction in quantity is the reduction «injection time».
Starting a cold engine
A rich mixture is needed to start a cold engine, because many of the fuel droplets condense on the inner walls of the injection system already on their way to the combustion chambers and do not participate in the combustion process. Therefore, it is necessary to enrich the mixture.
The cold start program takes care of this. During cold start control, the injection duration of the injectors is increased. Injection duration is affected by factors such as coolant temperature and engine speed. After a certain number of revolutions, the amount of fuel at a cold start is gradually reduced to normal.
Warm-up phase
After starting, the engine also needs a rich mixture for some time, because some fuel still continues to condense in the intake system. For this there is «post-launch enrichment». For a certain time, depending on the temperature, more fuel is supplied. The control unit receives the necessary information about the engine temperature from the coolant temperature sensor. A relatively viscous engine oil causes increased internal friction when the engine is cold. Therefore more effort is needed (richer mixture), to maintain the desired speed. The flow of an enriched mixture is provided by the already mentioned valve for stabilizing the engine speed in idling mode.
Idling
With closed throttle (released accelerator pedal) a small amount of air passes through the channel past the throttle valve. The amount of this air is determined by an air flow meter or pressure sensor and is supplemented with the necessary amount of fuel to obtain a mixture for idling. By the way, the idle mixture is richer than the normal mixture, which is done to ensure that the engine runs smoothly. At what point the idle mixture should be enriched, the control unit learns from the throttle valve potentiometer. How much air will pass through the bypass is determined by the idle speed stabilization valve.
Overclocking
If the accelerator pedal is suddenly depressed, this causes the acceleration mixture to become richer if the increase in the amount/mass of intake air per second exceeds a certain amount. Also, the acceleration signal comes from the throttle potentiometer. If the engine is still cold, then even more fuel is needed for acceleration. The control unit therefore recognizes the corresponding impulse from the air mass meter or the pressure sensor and the throttle valve potentiometer as an acceleration signal and increases the fuel supply.
Speed limitation
The injection system compares the current speed with the maximum speed of 6500 rpm and, if it is exceeded, simply stops the fuel supply (see also chapter «Engines»).
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