Fuel System
Fuel System Components
A vehicle fuel system is comprised of the following elements at a minimum: (Please note that
carburetion / fuel injection is handled in a separate section)
- Fuel Tank
- The fuel tank is the main storage for the fuel that runs the vehicle. Generally speaking, the
gas tank is generally found at, or under, the rear of the vehicle.
- Fuel Fill Hose
- The Fuel Fill Hose is the main connector from the gas cap to the fuel tank. This is the point where
the Gasoline (or other fuel) is put into the vehicle.
- Gas cap
- The gas cap seals the fill hose and is used to ensure that A) Gas does not spill out from the car,
and B) that the fuel system remains pressurized correctly (in vehicles that use pressurized systems).
- Fuel Pump
- There are two types of fuel pumps: Mechanical and Electric. In most cars you will have an electrical
fuel pump and you will find it in proximity of, or integrated into the fuel tank. If you are restoring a
particularly old/carbuerated vehicle it may have a mechanical pump. If this is the case, it will be
connected to the engine. Mechanical fuel pumps rely on the movement of the motor to draw fuel rather than
electrical power.
- Fuel Filter
- Depending on the age of your vehicle, you may not have a fuel filter. I've included it in the main section
because it is a critical component, especially in older systems. The fuel filter is contained at some point
within the fuel lines that draw gasoline from the fuel tank to the carburetor/fuel injectors. A good clean fuel
filter can save you significant repair time/costs on your carburetor/fuel injectors as it will ensure that
no old residue, rust, dirt or debris makes it to these systems.
- Fuel Lines
- The Fuel Lines connect all of the various Fuel System components.
- Fuel Gauge
- The fuel gauge exists as a display item in the vehicle's dashboard. It is intended to show to the driver the
actual amount of fuel in the fuel tank. On older cars it's common for fuel gagues (or their related part, the
sending unit) to be inaccurate. When you first start driving your classic car take time to learn how accurate the
system is. It'll save you from a long walk to the gas station if you run out of gas!
- Fuel Gauge Sending Unit
-
In terms of the fuel system, this may be your biggest headache. Sending units, at best, are generally a flawed
design. Generally, the sender is most accurate between 1/4 and 3/4 of a tank of gas. Outside of this the gauge
becomes progressively more innacurate as you reach the tank limits (full or empty).
Based on the age of the vehicle, the type of carburetion/fuel injection, and the emissions standards
in place at the time it may also have:
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- Fuel return lines
- Are generally the same type of line tubing as the main Fuel Line. These specific lines are used for a couple
purposes. Primarily they are used to return excess fuel to the gas tank for recirculation. Additionally they capture
gasoline vapours, which, as they are pushed back to the gas tank cool and condense back into liquid. In particular,
diesel powered fuel injected engines often use the fuel as a cooling mechanism for the fuel injector. They can
recirculate significant amounts of fuel.
- Emission Vapor Controls
- These are often used in combination with fuel return lines. The goal of this section of the overall
system is to ensure that gasoline vapors are not released into the ambient air. If this occurs a number
of bad things may happen: 1) The earth shattering kaboom of gasoline vapors igniting, 2) The unpleasant
smell of gasoline is routed into the interior of the vehicle, and 3) It can harm the environment.
- Fuel Pressure Regulator
-
Fuel Pressure Regulators are primarily found in fuel injected cars. Fuel injection, as opposed to
carburetion, is a high pressure system. The fuel pressure regulator ensures that the system
maintains the proper amount of pressurization.
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How it works
Some some of this may seem a little silly, as many components are pretty obvious to all of us.
Fundamentally, once you fill the tank with gasoline the system is "ready." When you start the car the
fuel pump begins the process of drawing fuel from the fuel tank, through the fuel lines and fuel filter,
to the system that controls fuel/air delivery to the engine (a carburetor or fuel injector). While the
car is running a continuous supply of fuel is delivered in this fasshion.
Carbureted Engines
The fuel system for this type of engine is generally a low pressure system. If the vehicle is equipped
with a mechanical fuel pump, the number of revolutions of the motor (RPMs) control how quickly fuel is
delivered. The faster the car is going (or revving) the greater the movement of the fuel pump and the
overall volume of fuel being delivered. If the vehicle is equipped with an electrical fuel pump the overall
process is the same, but some form of restrictor is necessary to ensure that the appropriate amount of
fuel is delivered. This can be a pressure regulator, an overflow system with return lines, or a vehicle
specific mechanism.
Fuel Injected Engines
Once the vehicle is started, providing that the gas cap was installed and sealing correctly, the
system becomes pressurized. Your modern car is probably fuel injected. Ever notice the release of air
when you go to add gasoline? This is the vehicle releasing the system pressure. The electric fuel pump
continuously pumps gasoline, ensuring that the system has the correct level of pressure. In addition to
the normal fuel delivery, it also passes through the pressure regulator which ensures that the fuel
pressure at the point of the Injector is correct so that the amount of fuel injected into the engine is
appropriate. Depending on the year and the vehicle in question, the level of the technology that controls
the system may be simple wiring type controls or a computer.
Emission controls
Emission controls are an add on to the basic fuel system, and vary in complexity based on the year, vehicle, and
legal controls in place at the time of manufacture. Fundamentally, they ensure that the appropriate amount
of fuel is delivered, excess fuel is returned to the gas tank, and hazardous vapors are not allowed to escape
the system. Because of the variability in this specific segment of the system, it is important for you to
review the technical information that specifically relates to your vehicle.
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