Fuel system procedures : Replacing a fuel filter

Replacing a fuel filter

Part 1. Preparation and safety

Objective

• Remove and replace a fuel filter.

Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection – such as rubber gloves and barrier cream
• Respiratory equipment – such as face masks and valved respirators

EFI fuel supply system - components

• Fuel filters
• Tanks & lines
• Fuel lines
• Fuel rail
• Fuel pressure regulator
• Injectors
• Tachometric relay
• Thermotime switch
• EFI sensors
• Potentiometer
• Auxiliary air valves
•  Idle speed control devices
• Inertia sensors

Fuel filters

It is very important to supply clean fuel to the fuel rail in EFI systems. Small particles of dirt can block an injection nozzle and cause an irregular spray pattern.
Any water in the fuel will corrode the inside of the injector - especially if the engine stands unused for long periods.
The first filtering occurs with a strainer or fine gauze in the fuel tank.
The next time filtering occurs at the in-line filter, on the high-pressure side of the pump. This is a large-capacity filter encased, in a steel shell or an aluminium housing. This housing must be rigid, to withstand the high pressures in the system.
The filter is a pleated paper type with pore size of about 10 microns. A fluted support plate keeps the filter stable in the housing. The filter is directional, and it must be fitted in the direction of fuel flow.
Final filtering occurs with a small conical filter at the fuel entry to the injector

EFI fuel supply components : Fuel pumps

• Fuel pumps

• Electric fuel pumps

• Mechanical fuel pumps

Fuel pumps

In an electronic fuel-injected engine, the fuel for the injectors must be pressurized before the engine can be started, so an electric fuel pump is necessary.
An electric rotary pump can be located in the tank, or externally, on the underside of the body.
Gasoline enters at one end and leaves at the other, so it is always full. This lubricates the pump motor and keeps it cool. The pumping element is a roller-cell device driven by an electric motor. A rotor disc is mounted eccentrically in the pump housing. It has recesses around its edge, containing metal rollers. As the disc rotates, centrifugal force pushes them outward. This forms a rotating seal, and fuel is carried round in the cavities formed between the rollers. Because of the eccentric mounting of the disc, these cavities expand as they pass the inlet, and contract passing the outlet. This pressurizes the fuel and forces it into the fuel line.
The pump can also be an impeller type, which is less noisy.
For a short time after an engine is switched off, engine temperature keeps rising, and that can cause excess vapor in the fuel lines. This pump stops this, with a non-return valve on its outlet, which maintains the pressure in the fuel line during that short time.
If a fuel blockage occurs further along the fuel line, it can overload the pump motor, and make it overheat. So a high-pressure relief valve inside the pump lets fuel keep circulating.
When the pump is mounted externally, a low-pressure pump can be used to supply fuel to the main pump’s inlet. This low-pressure pump is mounted in the fuel tank. It’s a centrifugal type, and electrical, and it operates in the same way as the other high-pressure pump.

EFI fuel supply : Simultaneous injection / Efficient combustion

• Simultaneous injection

• Efficient combustion

Simultaneous injection

In multi-point injection, the injectors can all be triggered at the same time. This is called simultaneous injection, and the injectors operate twice per cycle. That’s once each crankshaft revolution, each time delivering half the fuel for the cycle.
In a 6-cylinder engine, the injectors are triggered on every third ignition pulse.
In throttle-body systems, the central injector is normally triggered on every ignition pulse. However, if there are 2 injectors, alternate triggering may be used.
At idling speeds, the frequency may be less, to provide finer control.
The actual operating time of the injectors depends very much on battery voltage. The response time to lift the injector needle to the fully-open position is about 1 millisecond. If battery voltage is low, this response time takes longer, and the engine receives less fuel.
The ECU can compensate for this delay in opening time by extending the duration of the injection pulse.
In more sophisticated engine management systems, the control unit can control additional functions such as ignition timing, injection modes, idle speed, cooling fans, and fuel pump operation. To do this however, more inputs are needed.
To control ignition timing, some systems replace the distributor with a direct-fire ignition system. Between one ignition point, and the next, the ECU calculates when the ignition point will occur. It then triggers the ignition accordingly.

EFI fuel supply : Multi-point injection systems

Multi-point injection systems

In multi-point injection systems, the fuel pressure regulator has an inlet connection from the fuel rail, and an outlet that lets fuel return to the tank.
A control diaphragm and pressure spring determines the exposed opening of the outlet, and the amount of fuel that can return. So the strength of the pressure spring determines fuel pressure in the fuel rail, and keeps it at a fixed value.

EFI fuel supply : Modes of operation

EFI modes of operation

Indirect injection

Typical gasoline engines are usually equipped with indirect injection systems. They may be single point where the fuel is injected using one nozzle, usually in the throttle housing, or multi point where each cylinder has its own injector in the intake manifold. The nozzles may be opened using the pressure in the fuel system or there may be a solenoid on the injector that will pulse it open and closed in a duty cycle according to the desired fuel requirement.
Throttle-body injection
Electronic throttle-body injection (normally called TBI, though Ford Motor Company used the abbreviation, CFI) was introduced in the early 1980s as a transition technology to fully-electronic port injection. The system injects fuel into the throttle-body (a wet system), so fuel can condense and cling to the walls of the intake system. This system also resulted in harming emissions. Computer-controlled TBI was inexpensive and simple, however, and lasted well into the 1990s.
Central port injection
General Motors developed a new "in-between" technique called central port injection or CPI. It uses tubes from a central injector to spray fuel at the intake port rather than the throttle-body (it is a dry system). However, fuel is continuously injected to all ports simultaneously, which is less than optimal.
Sequential central point injection
GM refined the CPI system into a sequential central port injection (SCPI) system in the mid-1990s. It used valves to meter the fuel to just the cylinders that were in the intake phase. This worked well on paper, but the valves had a tendency to stick. Fuel injector cleaners sometimes worked, but the system remained problematic.

EFI fuel supply : Air supply ,Air volume

• Air supply
• Air volume

Air supply

In multi-point injection systems, the air required for the combustion of the fuel is led from the air filter, through the throttle valve, and into the common manifold, or plenum chamber. From here, individual intake runners, or pipes, branch off to each cylinder. All of these pipes are of equal length.
The design of the intake system determines how large an air mass can be drawn into a cylinder at any given engine RPM. This is where most advantage can be taken of electronic fuel injection, since it can achieve exactly uniform distribution of the air delivered to the cylinders.
With unobstructed passages to each cylinder, the cylinder fills with air as efficiently as possible. The breathing of the engine, or its volumetric efficiency, is improved. The more air crammed into the cylinder, the denser the air-fuel mixture, when ignition occurs.
This increases the thrust on the piston, and increases engine power output too.
The temperature of the air influences how dense the air-fuel mixture will be. Cold air is denser than hot air, so it has a greater mass in any given volume.
This is why, on most intake systems, the air entry to the intake is away from engine heat - to ensure the entry of cool air.
Since the manifold carries air only, it doesn’t need to be heated by coolant. Filtered air arrives at the intake port, as cold and dense as possible, ready for mixing with the fuel from the injector

EFI principles

Fuel injection is a technology used in internal combustion engines to mix the fuel with air prior to combustion.
As in a traditional carburetor, fuel is converted to a fine spray and mixed with air. However, where a traditional carburetor forces the incoming air through a venturi to pull the fuel into the air stream, a fuel injection system forces the fuel through nozzles under pressure to inject the fuel into the air stream without requiring a venturi.

EFI development

Frederick William Lanchester joined the Forward Gas Engine Company Birmingham, England in 1889. He carried out what was possibly the earliest experiments with fuel injection.
Indirect fuel injection has been used in diesel engines since the mid 1920s, almost from their introduction (due to the higher energy required for diesel to evaporate). The concept was adapted for use in petrol-powered aircraft during World War II, and direct injection was employed in some notable designs like the Daimler-Benz DB 603 and later versions of the Wright R-3350 used in the B-29 Superfortress.
An injection system developed by Robert Bosch GmbH|Bosch was first used in an automobile in 1955 with the introduction of the Mercedes-Benz 300SL. An electronic fuel injection system was also developed by the Bendix Corporation.

Basic EFI principles

Because of the need to comply with exhaust emission regulations, the modern gasoline engine requires a fuel system of extreme accuracy and long-term reliability. A correctly matched air-fuel ratio must be available at all times, and under all conditions. This is satisfactorily achieved by electronic fuel injection.
EFI is a pressurized, indirect-injection system, which uses solenoid-operated injectors with a fixed orifice. When they are energized, fuel passes through the injector body.
This arrangement is called a multi-point system. One injector is located in each intake manifold runner, or pipe, adjacent to each cylinder.

Carbureted system components

• The carburetor
• Mechanical fuel pumps
• Electric fuel pumps
• Tanks & lines
• Fuel lines
• Charcoal canister
• Carburetor filters

The carburetor

The carburetor supplies the engine with the correct air-fuel mixture for all conditions of operation.

• It atomizes the fuel and mixes it with air.
• It controls the delivery of this correct mixture to the engine.

Carburetors come in different designs.
This is a basic downdraft carburetor, with a fixed-size venturi. Fuel is pumped to the float bowl where a float and a needle valve control its level. The float bowl is open to the atmosphere. The barrel of the carburetor has an air horn and a venturi. A throttle valve below the venturi is linked to the accelerator pedal. Its action allows airflow into the carburetor barrel.

Carburetor operation

• Carburation
• Carburetor operation overview
• Carburetor systems
• Metering jets
• Accelerating
• Carburetor barrels

Carburation

This section looks at the basic principles of carburetors and carbureted systems.
The carburetor (American English; carburettor or carburetter in Commonwealth countries, "carb" for short) is a device which mixes air and fuel for an internal-combustion engine.
Carburetors are still found in small engines and in older or specialized automobiles such as those designed for stock car racing. However, most cars built since the early 1980s use computerized electronic fuel injection instead of carburetion.

Gasoline fuel system principles

• Gasoline fuel
• Gasoline fuel characteristics
• Controlling fuel burn
• Stoichiometric ratio
• Air density
• Fuel supply system
• Pressure & vacuum

Gasoline fuel

Petroleum or crude oil is taken out of the ground as a mix of impurities and highly flammable compounds of hydrogen and carbon, called hydrocarbons.
It is processed into many products, including petrol/gasoline and diesel fuel.
Gasoline is used in different forms in different engines.
It is very volatile, mixing easily with air to form gas or vapor. The more effectively liquid gasoline is changed into vapor, the more efficiently it burns in the engine, so high volatility is desirable.
And if liquid gasoline is heated, it is even more volatile.
However, if it vaporizes in the fuel line, bubbles of vapor can block the flow of fuel and stop the engine. This is called vapor lock.