Fuel Injectors:

In our last post we shed the light on the importance of the fuel pump in the system that feed the engine the highly flammable liquid responsible for the combustion inside its chambers. However, the fuel is easier to combust in the vapor state than the liquid.

Thus, the fuel injector connecting the fuel rail, containing the fuel provided from the fuel pump, to the combustion chamber is responsible for spraying the fuel on top of the piston creating high amount of fuel vapor easy to ignite.

The injector’s exterior is made of strong lasting plastic with metallic extremities that connect to the fuel rail on one side and the engine head on the other. Both ends are sealed with thick O-rings that keep the fuel pressure from escaping.
Inside the injector, a pintle pushed by the fuel pressure blocks it from flowing into the combustion chamber. When the injector is activated by the ECM command (Usually by a PWM signal), the solenoid inside the injector creates an electromagnetic field that moves the pintle letting the fuel through the spray tip.

Common failures in injectors are:

- Clogged filter: It causes a lack of fuel and reduced flow due to dirt in the system (e.g corrosion from the fuel system).
- Badly closing pintle: The injector leaks fuel inside cylinder due to a deformation in the spring or the pintle.
- Warn out seals: It results in fuel leaking to the outside of the engine, the seals dry up due to time or break because of bad installation or even wrong fuel type.
- Dead/short-circuited solenoid.

The spraying pattern of the injector is very important to the efficiency and quality of the combustion.
Fuel vapor burns much faster than fuel in the liquid state, and it burns best when sprayed on the biggest area possible.
Therefore, for a good combustion, we need a fully atomized fuel equally distributed in the combustion chamber.
The picture below shows how the spraying pattern of an injector may vary.

Injector testing is done on a special tool, where the injector’s efficacy can be tested according to the voltage supply, the injector’s spraying pattern can be closely observed and the injector can be checked for any external or internal leakage.

A dead injector will cause a rough misfire and stalling, while a dying injector will cause a bad air-fuel mixture, an increase in fuel consumption, bad emissions and in an internally leaking case, a flooded engine and fuel-engine oil mixture inside the oil system.