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Auto Repair: Basic Fuel System Components

car at fuel pump

Whether your vehicle is more than 20 years old or just 20 days old, has fuel injectors or a carburetor, it probably has the same basic parts in its fuel system with one exception: On modern vehicles, the fuel system — along with most other systems — is controlled by the engine control unit (ECU). The ECU controls the fuel/air mixture and other fuel system operations based on inputs from a mass air flow meter, a throttle position sensor, and anoxygen sensor. As you can see in Figure 7-1, it's located under the hood.

Fuel Tank The fuel tank is a metal or plastic composite container that's usually locatedunder the trunk compartment (refer to Figure 7-1), although some vehicles have some fairly interesting alternative locations for it. If you're not surewhere your fuel tank is and you can't find it just by looking under the car,your owner's manual or mechanic can show you where it's located.

Inside the fuel tank is a little float that moves up and down as the fuel level in the tank increases or decreases. The float is at its highest when the tank is full. Its position relative to the top of the tank is picked up by a sensor that sends an electronic signal from the tank to the fuel gauge on your dashboard so that you can tell when you have to buy more fuel.

Figure 7-1: A fuel system.

Fuel Lines and Fuel Pump

The fuel pump (see Figure 7-2) pumps fuel through the fuel lines that run under your vehicle from the fuel tank to the fuel injectors (or to the carburetor on older vehicles). Engines with fuel injection use an electric fuel pump that may be located in or near the fuel tank. (On most carbureted vehicles, amechanical pump is under the hood.)

If your vehicle is suffering from fuel-system problems, remember that a number of things can be the cause. Most fuel pumps are located inside the fuel tank or so far under the vehicle that you can't reach them easily without a hoist or crawling under your vehicle, so have a professional check it for you.

Figure 7-2: An electric fuel pump located in a fuel tank.

Tip: If your fuel pump does need replacing, ask your service facility to replace it with a new one, as their charges for rebuilding yours would probably be more expensive than for just installing a new one. Be sure that they guarantee the pump for at least a year. Hopefully, it will last much longer than that.

From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.

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