Auto Service Professional

OCT 2017

Magazine for the auto service professional

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12 | ASP October 2017 Technical Fuel Pump 101 e basics of fuel pump diagnosis and repair By Jacques Gordon T he most common cause of fuel pump failure is frequently running the tank low on fuel, which causes the motor to overheat. e second most common cause is fuel contamination, usually dirt and rust par- ticles that clog the fuel strainer and prevent the pump from drawing enough fuel under high engine load. If enough contamination gets past the pump's intake strainer, it can actually jam the pump and stop the engine immediately. Diagnosing fuel pressure problems is often tricky because the problem can be something other than the fuel pump. To help you avoid misdiagnosis and comebacks, we're going to review the components of a fuel pump assem- bly, describe some diagnostic techniques, and discuss how to give replacement fuel pumps a good chance at a long service life. We'll focus only on port fuel injection systems that use the electric pump to generate all the pressure in the system, but most of this information can also apply to the fuel delivery system of direct-injection engines, too. Fuel pump e complete fuel pump assembly might include a fuel gauge sending unit, a pressure regulator valve, a fuel tank pressure sensor, a pump intake strainer and/or the main fuel system filter, and of course the electric fuel pump. An electric fuel pump consists of two parts: a small brush-type DC motor and the pump itself. is assembly is submerged in a reservoir of fuel that keeps the motor cool and prevents air from getting to the motor, thus eliminating the risk of fire or explosion. Electric fuel pumps are among the most reliable parts of a car. Under normal condi- tions, it's not uncommon for a pump to last the whole life of the vehicle. When it finally quits, it's because the motor is worn out and can't develop enough torque to generate the correct fuel pressure. Here are the basics for what it takes to diagnose a problem and perform a profitable repair. Fuel pump reservoir Motor/pump assembly with integral pressure regulator Tank vent and E VAP connections Fuel tank pressure sensor Pump and gauge electrical connections Fuel gauge float Fuel outlet Photo courtesy of Carter Fuel Systems

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