EFI fuel supply : Simultaneous injection / Efficient combustion

• Simultaneous injection

• Efficient combustion

Simultaneous injection

In multi-point injection, the injectors can all be triggered at the same time. This is called simultaneous injection, and the injectors operate twice per cycle. That’s once each crankshaft revolution, each time delivering half the fuel for the cycle.
In a 6-cylinder engine, the injectors are triggered on every third ignition pulse.
In throttle-body systems, the central injector is normally triggered on every ignition pulse. However, if there are 2 injectors, alternate triggering may be used.
At idling speeds, the frequency may be less, to provide finer control.
The actual operating time of the injectors depends very much on battery voltage. The response time to lift the injector needle to the fully-open position is about 1 millisecond. If battery voltage is low, this response time takes longer, and the engine receives less fuel.
The ECU can compensate for this delay in opening time by extending the duration of the injection pulse.
In more sophisticated engine management systems, the control unit can control additional functions such as ignition timing, injection modes, idle speed, cooling fans, and fuel pump operation. To do this however, more inputs are needed.
To control ignition timing, some systems replace the distributor with a direct-fire ignition system. Between one ignition point, and the next, the ECU calculates when the ignition point will occur. It then triggers the ignition accordingly.

Ignition can be varied according to load, speed, coolant temperature, cranking speed, and battery voltage.
Identifying number one cylinder and the camshaft position, allows different injection modes to be used.
Sequential injection means injection occurs in the sequence of the firing order. Each injector opens once only in each cycle, to deliver the fuel needed.
Added load placed on the engine during idle, can be compensated for by increasing the passageway of an idle speed control device. This lets more air by-pass the throttle plate. This air has been measured by the airflow meter, so extra fuel is metered to maintain the same air-fuel ratio. The extra mixture thus delivered increases engine torque, and maintains idle speed.

Efficient combustion

For efficient operation of the catalytic converter, the mixture ratio must be maintained close to the stoichiometric ratio - 14.7 parts of air to one part of fuel.
Efficiency of combustion can be monitored by measuring the percentage of oxygen in the exhaust gas. A high percentage may mean the mixture entering the cylinder is too lean.
The oxygen sensor in the exhaust manifold, or in the engine pipe, tells the ECU how much oxygen is in the exhaust gas. The ECU then varies injector opening time to achieve a correct mixture ratio.
Feedback also lets fuel settings change as components age. This is called adaptive learning. The ECU memorizes its fuel settings for different operating conditions, and stores them for future use.
If a fault occurs in a component or part of a system, a fault code can be displayed on the check engine lamp in front of the driver. Alternatively, a scanning tool can be connected to a diagnostic terminal, and information on the fault can be analyzed.
Although most injectors operate at the nominal battery voltage of 12 volts, many sensors have a reference voltage of 5 volts. This is done by a voltage regulator in the control unit. It gives more accurate signaling, as fluctuations due to changes in battery voltage do not occur.