However, if the contacts are loose, corroded, contaminated or simply not big enough to handle the current flow, resistance increases. If the connection is tight and remains clean, the resistance is almost nothing.
Eventually the motor becomes too weak to generate proper fuel pressure, and if the resistance gets high enough, the motor won’t even run.Īs current flows through a circuit, the most common place for resistance to occur (other than the load) is in a connector. This creates electrical resistance that reduces current flow through the motor and therefore reduces the motor’s power. If the brushes are overheated often enough, a coating of burnt carbon builds up on the contacts. Soon the ends of the brushes get so hot that microscopic particles of carbon burn off and stick to the copper contacts. This heat is carried away by fuel flowing through the pump, so when the low-fuel warning light turns on there’s not much fuel left in the tank to absorb all that heat. Even on a cold day the fuel pump motor typically runs at about 100 degrees Fahrenheit. Most of that heat is concentrated at the point of highest resistance, and in a brush-type motor, it’s where the carbon brushes touch the rotating copper contacts (commutator bars). As electrical current flows through a circuit, it naturally generates heat. The only wear parts on this whole assembly are the motor’s brushes. This 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. An electric fuel pump consists of two parts: a small brush-type DC motor and the pump itself. The 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. 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.
To help you avoid misdiagnosis and comebacks, we’re going to review the components of a fuel pump assembly, describe some diagnostic techniques, and discuss how to give replacement fuel pumps a good chance at a long service life. If enough contamination gets past the pump’s intake strainer, it can actually jam the pump and stop the engine immediately.ĭiagnosing fuel pressure problems is often tricky because the problem can be something other than the fuel pump. The second most common cause is fuel contamination, usually dirt and rust particles that clog the fuel strainer and prevent the pump from drawing enough fuel under high engine load. The most common cause of fuel pump failure is frequently running the tank low on fuel, which causes the motor to overheat. Here are the basics for what it takes to diagnose a problem and perform a profitable repair.
When it finally quits, it’s because the motor is worn out and can’t develop enough torque to generate the correct fuel pressure. Under normal conditions, it’s not uncommon for a pump to last the whole life of the vehicle. Electric fuel pumps are among the most reliable parts of a car.