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Injector drive time in case of multi-point injection (MPI) is controlled as follows according
to driving conditions.
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Fuel injection to each cylinder is done by driving the injector at optimum timing while
it is in exhaust process based on the crank angle sensor signal. Engine-ECU compares the crank angle
sensor output pulse signal and cam position sensor output pulse signal to identify the cylinder.
Using this as a base, it performs sequential injection in the sequence of cylinders 1, 2, 3,
4, 5, 6.
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In addition to the synchronizing fuel injection with the crank angle sensor signal during
acceleration, the volume of fuel is injected according to the extent of the acceleration.
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The figure shows the flow for injector drive time calculation. Basic drive time is decided
based on the air flow sensor signal (intake air volume signal) and crank angle sensor signal (engine
rotation signal). This basic drive time is compensated according to signals from various sensors
and optimum injector drive time (fuel injection volume) is calculated according to driving conditions.
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Fuel injection is performed once per cycle for each cylinder. Basic drive time refers
to fuel injection volume (injector drive time) to achieve theoretical air-fuel ratio for the
intake air volume of 1 cycle of 1 cylinder. Fuel injection volume changes according to the pressure
difference (injected fuel pressure) between manifold pressure and fuel pressure (constant).
So, injected fuel pressure compensation is made to injector drive time for theoretical air-fuel
ratio to arrive at basic drive time.
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Intake air volume of each cycle of 1 cylinder is calculated by engine-ECU based on the
air flow sensor signal and crank angle sensor signal. Also, during engine start, the map value prescribed
by the coolant temperature sensor signal is used as basic drive time.
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After calculating the injector basic drive time, the engine-ECU makes the following compensations
to control the optimum fuel injection volume according to driving conditions.
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Compensations
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Content
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Oxygen sensor feedback compensation
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The oxygen sensor signal is used for making the compensation to get
air-fuel ratio with best cleaning efficiency of the 3-way catalytic converter. This compensation
might not be made sometimes in order to improve drivability, depending on driving conditions.
(Air-fuel ratio compensation is made.)
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Air-fuel ratio compensation
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Under driving conditions where oxygen sensor feedback compensation
is not performed, compensation is made based on pre-set map values that vary according to engine
speed and intake air volume.
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Engine coolant temperature compensation
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Compensation is made according to the engine coolant temperature.
The lower the engine coolant temperature, the greater the fuel injection volume.
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Acceleration/ Deceleration compensation
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Compensation is made according to change in intake air volume. During
acceleration, fuel injection volume is increased. Also, during deceleration, fuel injection
volume is decreased.
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Fuel injection compensation
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Compensation is made according to the pressure difference between
atmospheric pressure and manifold absolute pressure. The greater the difference in pressure,
the shorter the injector drive time.
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Battery voltage compensation
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Compensation is made depending on battery voltage. The lower the
battery voltage, the greater the injector drive signal time.
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Learning value for fuel compensation
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Compensation amount is learned to compensate feedback of oxygen sensor.
This allows system to compensate in accordance with engine characteristics.
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Engine-ECU limits fuel when decelerating downhill to prevent excessive rise of catalytic
converter temperature and to improve fuel efficiency.
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When engine speed exceeds a prescribed limit (7,500 r/min), engine-ECU cuts fuel supply
to prevent overrunning and thus protect the engine. Also, if engine speed exceeds 4,000 r/min for
15 seconds while vehicle is stationary (no load), it cuts fuel supply to protect the engine.
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