Injection system components

The list of components is pretty long and it generally varies from one brand and one model to the next. Some systems will only use part of these components. Each manufacturer has to make business decisions based on production costs, engine requirements and target customers.


The first one on the list is the throttle positioning sensor (TPS), which determines the opening angle of the throttle and, consequently, the air flow directed to the engine. The more you want to accelerate, the more the sensor will shift and generate a tension to assign an opening angle to the throttle. This tension will have an influence on the air-fuel mixture that will be injected.

Meanwhile, two nearly identical sensors work in opposition: the Baro and the Map. The former senses air pressure and calculates the value of the intake air. Depending on the season and weather, the air pressure (density) will vary, thus altering the ideal air-fuel ratio. For example, on cold winter days, the pressure will increase. Conversely, it will decrease as summer approaches and the temperature gets warmer. The average (ideal) air pressure, calculated at sea level, is 14.7 PSI (101.35 kPa). Pressure changes are often negligible, but their impact is significant enough to require a correction of the injection timing.

The Map sensor monitors the negative air pressure (vaccum) in the intake manifold, between the throttle and piston. The Baro and Map calculate the difference between the air pressure inside and outside the engine. They then send a signal to the computer (ECU). Again, this will have an influence on the air-fuel mixture that will be injected.

* Graph of injection based on the throttle position