In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few:
- Mass airflow sensor - Tells the ECU the mass of air entering the engine
- Oxygen sensor(s) - Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly
- Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary
- Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature
- Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)
- Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold
- The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.
- Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse width
There are two main types of control for multi-port systems: The fuel injectors can all open at the same time, or each one can open just before the intake valve for its cylinder opens (this is called sequential multi-port fuel injection).
The advantage of sequential fuel injection is that if the driver makes a sudden change, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine.