Demonstrate knowledge of an electronic fuel injection (EFI) system Flashcards
What is meant by the term stoichiometric ratio?
The air fuel mixture ratio that gives the chemically correct (ideal) combination of air and fuel is called the stoichiometric ratio.
- What is a lean air fuel mixture and how does it affect vehicle
performance?
An air fuel mixture that has more air than the ideal stoichiometric ratio. It will increase fuel economy but will decrease engine power if too lean.
- What is a rich air fuel mixture and how does it affect vehicle
performance?
An air fuel mixture that has more fuel than the ideal stoichiometric ratio. It will increase engine power but will decrease fuel economy. However, if too rich engine power will decrease, exhaust emissions will rise and spark plugs will be fouled.
Describe what should happen in the combustion chamber during
normal combustion.
The air fuel mixture is ignited by the spark plug and burns evenly across the
top of the piston
How can “detonation” affect an engines performance?
Increased heat and pressure will cause the fuel mixture to combust by itself.
Can lead to damaged pistons and premature engine wear.
How can “spark knock” affect an engines performance?
Incorrect ignition timing can cause the spark plug to fire too soon in relation
to the correct piston position. This condition will lead to engine damage, may
even damage the piston.
How can “dieseling” affect an engines performance?
An overheated engine may cause the air fuel mixture to ignite without the
use of voltage at the spark plug. Can lead to damaged pistons and
premature engine wear.
What does an
“expansion chamber” do in a fuel tank?
Prevents fuel tank from being completely filled as a result of heated fuel.
What does an “anti blow back valve” do in a fuel tank?
Prevents fuel tank overfill when refilling.
what does the “pick up tube”in a fuel tank do?
Allows fuel to be drawn out of the fuel tank.
what does the “Pressure/vacuum valve” in a fuel tank do?
Allows air to enter the tank and pressure to release.
What does a filter do for the fuel system?
Helps prevent contaminants from entering the fuel system.
what does the filler cap do in a fuel tank?
Prevents the escape of fuel and fuel vapours.
How is fuel supplied to an EFI system?
Fuel is supplied into the EFI system by an electric fuel pump. The pump is
typically located in or near the fuel tank. It supplies fuel at a high pressure to
the fuel rail where the pressure is regulated to about 3 bar (about 44 psi)
How is fuel metered and delivered into the engine?
The fuel is delivered into the inlet manifold or combustion chamber (direct
injection) by an electronically controlled injector which is attached to the fuel
rail. The volume of fuel being injected is controlled by the ECU which
controls the time each injector is open based on input sensor signals.
