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.

Fuel pump

 
The vehicle’s engine alone is nothing but a big air compressor. It is not until we add the correct amount of fuel to the mix that we will achieve a good combustion able to create enough power to move the car. The only component pumping gasoline to the engine is the fuel pump.

Types of fuel pumps:

Early cars were equipped with mechanical pumps located on the engine block. The most common mechanical pumps are made of a diaphragm and a spring that are pushed by a metallic lever excited by the engine’s camshaft. Therefore, the pumping frequency is proportional to the engine speed in this type of fuel pumps.
Mechanical pumps were used with carburetors and later abandoned in the injector era due to their low output pressure (less than 1 bar).

 

 

New cars have electric fuel pumps, they are mostly located in the fuel tank and able to generate more than 10 times the pressure of a mechanical pump.
This kind of fuel pumps are operated, most commonly, by a 12V two wires connector that feeds the motor’s brushes which provide the electricity needed to rotate the armature that is connected to the impeller. The impeller is responsible to pump the fuel from its holes to the inside of the pump (passing through the armature/rotor chamber) and to the top output neck of the fuel pump.

The newest technology in the market at the moment is brushless fuel pumps which are electrically more efficient.

Electric fuel pump specifications:

Electric fuel pumps datasheets are very important, they indicate the flow and pressure of the fuel vs the voltage and current fed, the electric efficiency (which helps the customer to understand the amount of heat generated as well), type of fuel that is able to handle, and the mechanical valves distribution (One-way valves, check valves…).
These information are critical to understand the amount of fuel delivered to the engine and the reliability of the pump.

The performance of the car is directly affected by the efficiency of the fuel pump. When the fuel pump starts to die, it will consume more current, the impeller will rotate with lower speed (a full rotation will take more than 7 ms), thus it will deliver less fuel than expected.

Causes and symptoms:

A broken fuel pump can be caused by:

·         Dirt and particles in the fuel: (Even small particles from the filter or the sealant might cause damage to the pump.

·         Dry running the pump: The fuel lubricates and cools the pump; a dry run will lead to the destruction of the inner parts of the pump.

·         High voltage and current feed: Burns and overheats electric components which results in short circuits.

·         Time: Like any other component, the fuel pump has a lifespan that varies from a car/brand to another.

·         Incorrect fuel type.

·         Low fuel level: Low fuel level will increase the chances of the fuel pump getting dirt into its system or running dry for a short time in corners

A broken fuel pump will reduce the power and the fuel efficiency of the engine while increasing the vehicle’s emissions. In addition, it might affect the starting time, cause random bangs and stall the vehicle.

Conclusion:

The fuel pump is the main character when looking into the vehicle’s power. It is the only component responsible for delivering fuel to the injectors.
A fuel pump giving up can be diagnosed by a lack of performance, higher fuel consumption and sveral mechanically noticed symptoms like bangs, vehicle stalls and an increase in the starting time.
Numerous causes can kill a fuel pump. Mainly related to the electric voltage fed, to the quality, type and quantity of the fuel that the fuel pump operates usually in.

A fuel pump in general is not a maintenance part, it is changed when it starts to fail, and should survive more than 100 000 miles.