Fuel Injection Systems

Question 1

Fuel Injection

Answer 1

An alternative to a carburettor

Continuous flow injection system is most common

Question 2

Fuel Pump

Answer 2

An engine driven pump that supplies fuel under pressure for the system

Question 3

Fuel/Air Control Unit

Answer 3

Takes the place of the carburettor and controls the airflow to the engine through a butterfly valve
Senses the amount of air flowing to the engine and meters the correct amount of fuel to the fuel manifold unit
Fuel pump delivers fuel to the fuel control unit

Question 4

Fuel Manifold Unit

Answer 4

On top of the engine
From here a separate fuel line carries fuel to the discharge nozzle in each intake manifold, ensuring strength in each cylinder will be correct

Question 5

Fuel Discharge Nozzles/Injectors

Answer 5

Inject fuel into the intake, at a high pressure to ensure it is vaporised, where it mixes with air and enters the cylinder through the intake valve

Question 6

Fuel Pressure/Fuel Flow Gauge

Answer 6

Pressure is measured before the fuel manifold valve (an assumption is made that a given pressure means a certain flow rate)
A blockage may result in a high pressure and a faulty reading as high fuel flow

Question 7

Advantages of Fuel Injection Over Carburettors

Answer 7

1. Will operate in sustained unusual attitudes
2. Mixture strength can be controlled more precisely
3. Fuel reaches the cylinder faster and acceleration is better as the fuel is injected immediately adjacent to the intake valve
4. The fuel is distributed more evenly, with less chance of detonation and better power output
5. Are not prone to icing problems

Question 8

Disadvantages of Fuel Injection over Carburettors

Answer 8

1. They are more complex and expensive
2. More susceptible to fuel contamination due to very fine fuel lines
3. More prone to fuel vaporisation as the fuel lines pass close to the engine and cylinder heads
4. Vapour locks make it hard to start a hot engine