Woodstock Auto Repair

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Car Care - Fuel & Air Intake

  1. Air Filter
  2. Carburetion
  3. Fuel Filter
  4. Fuel Injection
  5. Fuel Pump
  6. Fuel Storage
  7. Turbo & Supercharger


Air Filter

Description: The typical air filter is a disposable, pleated-paper element with a sealing gasket made of synthetic material. Filters come in two main types: the panel style as used on most fuel-injected cars and the radial style, which is usually used on carbureted vehicles.

Purpose: The air filter traps dirt particles, which can cause damage to engine cylinders, walls, pistons and piston rings. The air filter also plays a role in keeping contaminants off the airflow sensor (some fuel-injected cars) and sometimes in cleaning the air that enters the crankcase for crankcase ventilation. The air filter also serves as a silencer for your car's intake system. Your car's engine can use close to 40,000 litres of air for every 3.5 litres of fuel burned, so it's easy to see how big a job the air filter has.

Maintenance Tips/Suggestions: Although your car's owner's manual may specify an inspection interval for the air filter, it's really best that it be checked at every oil change. Dirty and dusty driving conditions will require more frequent filter replacements, so keep this in mind. Driving with a dirty filter restricts the air entering the engine, and if severe, can impact fuel economy and performance. If you decide to change the filter yourself, always do so with the engine off. Never start or run the engine with the air filter out of place. Most filters can be easily replaced by removing snap clips, a clamp or several screws. Make sure you use the filter specified for your car's engine; do not try to make a filter fit. An improperly fitting filter can allow unfiltered air into the engine, causing engine damage.


Description: Carburetion refers to the use of a carburetor as a means of controlling an engine's air/fuel ratio. Carburetors were used on most cars through the mid-1980s, when carmakers began a large-scale changeover to fuel injection. A carburetor holds fuel in a small reservoir called a float bowl. This reservoir is connected to a passageway leading to a venturi, a device that uses pressure differential to help meter fuel into the engine. Conventionally referred to as "barrels", it refers to the number of venturis in the carburetor. A one-barrel carburetor has one venturi; a two-barrel carburetor has two venturis, and so on, up to four venturis. Around 1980, carmakers began to add mixture control solenoids and other electronic devices to carburetors, to make them more effective by allowing additional control through an electronic engine control system.

Purpose: The carburetor mixes fuel with air in the right ratios for all engine-operating conditions.


Maintenance Tips/Suggestions: Replace the fuel filter once a year. If your car demonstrates a loss of performance or fuel economy, have the engine performance evaluated by a good shop with qualified technicians. The carburetor's health will also be checked out at this time. Other symptoms of carburetor problems include hard starting, stalling, hesitation, rough idle, black smoke from the tailpipe, or failing an emissions test. If you experience any of these problems, have them checked out at once to avoid more costly repairs.

Fuel Filter

Description: The typical fuel filter for most fuel-injected cars consists of a high-pressure canister filled with filtering media. Filters may have clamped, threaded or special fittings to ensure reliable connection to the fuel system. Filters for carbureted engines may be located at the inlet of the carburetor or inline. Filters for carbureted engines do not need to withstand the same pressures as those for fuel-injected engines.

Purpose: Fuel filters trap harmful contaminants that may cause problems with carburetors and intricate fuel injectors. Fuel filters for carbureted engines only clean the fuel before it enters the float bowl. Injection filters, on the other hand, clean the fuel whenever the fuel pump runs (unless the fuel injection system is a returnless design). Fuel moves continuously up the supply side, through the filter to the fuel rail or throttle body. The fuel that doesn't make it into the engine returns to the tank and the whole process starts over again. With a full tank of gas, the filter may clean the volume of fuel in the tank many times before it's all used.

Maintenance Tips/Suggestions: On carbureted cars, replace the filter once a year. On cars with fuel injection, some carmakers don't recommend replacing the filter at all during the first 170,000 kilometres of normal†driving. Since normal usually constitutes severe driving because of less than normal conditions, it's best to replace the filter every two years or 40,000 kilometres. A contaminated filter can restrict fuel flow from your car's electric fuel pump, eventually taking a toll on its life. Frequent filter replacements remove all doubt about whether the filter may cause other problems down the road.

Most filters on domestic cars and trucks hide underneath on the frame or body. Just the opposite is true on the imports. They usually put their filters somewhere in the engine compartment. If you decide to change the filter yourself, be careful. Fuel injection systems maintain pressure in the lines that must be relieved prior to filter replacement. Don't forget that gasoline is extremely flammable. Procedures vary for relieving pressure. Also, some filters require special tools to replace the fuel filter. Because of these technicalities and because of most filter locations, it's best to have your car's fuel filter replaced by a qualified service professional.

Fuel Injection

Description: Fuel injection consists of a throttle body to control airflow, the fuel injectors, various engine sensors, an electric fuel pump and a fuel filter. The system is controlled by the car's powertrain control module (PCM), which makes all decisions for controlling the injection system. Most early fuel injection systems used a throttle-body design, where one or more injectors were mounted on a throttle body, resembling a carburetor. Use of the throttle body system faded away gradually as multi-port fuel injection became more prevalent. Multi-port uses a separate fuel injector for each cylinder, located near each cylinder's intake valve port. Virtually all engines now use multi-port injection.

Purpose: Fuel injection delivers fuel to the engine in exactly the right amount for all engine-operating conditions. Not only does the system provide better control for fuel economy, performance and emissions, it also does away with many of the maintenance requirements of a carburetor.

Maintenance Tips/Suggestions: On cars with fuel injection, some carmakers don't recommend replacing the filter at all during the first 170,000 kilometres of normal driving. Since normal usually constitutes severe driving because of less than normal conditions, it's best to replace the filter every two years or 40,000 kilometres. A contaminated filter can restrict fuel flow from your car's electric fuel pump, eventually taking a toll on its life. Frequent filter replacements remove all doubt about whether the filter may cause other problems down the road.

On 1996 and newer vehicles, your car's fuel injection system is integrated with a second-generation onboard diagnostic system, known as OBDII. The PCM stores a Diagnostic Trouble Code (DTC) when it detects a problem in one of the monitored circuits. A professional technician can access this information using a scan tool connected to the vehicle's Data Link Connector (DLC). Although many DTCs are sensor-related, it does not necessarily indicate a faulty sensor. There may be problems in that sensor's circuit, or there may be several interrelated problems.

Areas of the country with an emissions testing program are placing added value on OBDII checks, where this technology may be used in place of tailpipe testing. The system also alerts you with a Malfunction Indicator Lamp (MIL), indicating that the system has detected a problem, which could cause excessive emissions. This light is usually labelled SERVICE ENGINE SOON or CHECK ENGINE. If the light appears, you should have its cause investigated by a professional technician at your earliest opportunity. If the light flashes, the condition is more severe and must be checked out immediately to prevent damage to the catalytic converter.

Fuel Pump

Description: A mechanical fuel pump is most often used on cars with carburetors. This type of pump produces low pressure and is usually driven by the engine. Cars all use electric fuel pumps nowadays because of the universal application of fuel injection and its need for higher pressures. Electric fuel pumps are almost always located inside the gas tank, but there are some applications where the pump may be located along the frame or uni-body channel. The pump has a strainer at its pickup to filter out contaminants and uses an electric motor for power. Fuel is used as a lubricant and coolant for the motor. The electric fuel pump has its own electrical control circuit, typically consisting of wiring, a fuse and a relay. This circuit interacts with the car's powertrain control module (PCM), which governs and monitors fuel pump operation.

Purpose: The fuel pump provides fuel with the proper pressure and volume for delivery by the carburetor or fuel injection system. The electric fuel pump circuit also employs various safeties that stop the pump from running in the event of an accident.

Maintenance Tips/Suggestions: Mechanical fuel pumps require no maintenance, but should be replaced at the first sign of a problem. Pressure or volume may drop off, giving an early warning sign of impending pump failure. A professional service technician can usually identify a pump problem quickly. With fuel-injected vehicles, regular fuel filter changes can help extend the life of the electric fuel pump. It's best to replace the filter every two years or 40,000 kilometres. A contaminated filter can restrict fuel flow from the electric fuel pump, eventually taking a toll on its life.

You can also help protect the pump by keeping the tank at least half-full at all times. Since fuel cools the pump, having plenty of fuel in the tank helps keep the pump from getting too warm, which could damage it.

Another good reason to keep the gas tank at least half-full is to reduce the chances of sediment pick-up at the fuel pump inlet strainer. A restricted strainer can starve the pump, causing it to overheat and fail. If you own a Ford or Lincoln-Mercury vehicle, check your owner's manual for the location of the fuel pump shut-off switch. This switch is designed to electrically disconnect the fuel pump in the event of an accident. Sometimes, an abrupt jarring of your car may be enough to cause this switch to open. It's good to know where the switch is so you can try resetting it if your car does not start.

A faulty electric fuel pump can cause various symptoms including a loud pump whine, engine no-start, hesitation, poor performance and stalling. If your car demonstrates any of these performance problems, have it checked out by a qualified service technician. Replacing the fuel pump generally involves removal of the fuel tank.

Fuel Storage

Description: The fuel tank is usually made of stamped steel or plastic. The tank is held in place with steel straps. In some cases, a bracket-and-strap arrangement is used.

Purpose: The fuel tank stores gasoline for the engine, holds the electric fuel pump and sending unit, and provides a connection to the vapour collection/recovery components of the emissions system. The tank also has a filler neck, which restricts fuelling to unleaded fuel nozzles. On 1996 and newer cars, the mouth of the filler neck is designed specially for OBDII-compatible gas caps.


Maintenance Tips/Suggestions: Unless damaged, fuel tanks last for the life of the vehicle. On many cars, the fuel tank needs to be removed in order to replace the fuel pump. On 1996 and newer cars, a light on the dash, labelled SERVICE ENGINE SOON or CHECK ENGINE may turn on if the gas cap is left loose after refuelling. Make sure the gas cap is always installed properly after you refuel. Turn the cap to the right until it clicks in place.

Turbo & Supercharger

Description: A turbocharger uses an exhaust-gas driven turbine wheel, which drives a compressor wheel to boost air delivery to the engine. A supercharger uses mechanically driven rotors, usually from a belt, to boost air delivery to the engine.

Purpose: Turbochargers and superchargers enable increased burning of air and fuel by forcing more of it into the engine's cylinders, thereby improving an engine's breathing characteristics.

Maintenance Tips/Suggestions: Check your car's owner's manual for maintenance requirements of the turbocharger or supercharger. The turbocharger or supercharger on your car's engine will last for many thousands of kilometres if cared for properly through a regular engine maintenance regimen. This includes regular oil and filter changes, engine performance check-ups, and cooling system maintenance. If you notice that engine performance drops off, that the engine is using oil, or notice other problems with coolant temperature or oil pressure, it's wise to have these looked into as soon as possible by a qualified professional.