What’s a Fuel Pump?

The Fuel Pump in your car is usually the most important component in your car or some other type of internal combustion engined device. A lot of engines - like some older engines that go on motorcycles - are the type of engines that don’t need a Fuel Pump .. at all. In most cases, carbureted engines use low pressure mechanical pumps that are typically mounted to outside of the actual fuel tank. Fuel Injected Engines a lot of the times use an electric Fuel Pump - this is mounted on the inside of the fuel tank.

Before everyone started getting crazy about Electronic Fuel Injection, most of the carbureted car engines used a mechanical Fuel Pump to transfer fuel from the actual Fuel Tank into the fuel blows of the installed carburetor. Mostly all of the mechanical fuel pumps are known as something called diaphragm pumps. These pumps are a type of positive displacement pump.

Diaphragm pumps have a pump chamber where the volume is either increased or decreased by the flexing of a diaphragm that just so happens to be .. flexible; it’s most similar to the action of your typical piston pump. There’s something called a check valve and it’s located at both the inlet ports AND the outlet ports of the pump chamber. This is supposed to technically force the fuel to flow in one direction and one direction only.

The specific designs can vary often, but in the most common layout, these pumps are usually bolted onto either the engine block or the head. In addition, the engine’s camshaft is made to have an extra eccentric lobe that’s supposed to operate a lever on the pump either directly or by a pushrod.

The carburetor is normally supposed to contain a float bowl where the left over fuel is pumped. When the fuel in the float boat exceeds a specific level, or when it overflows, the inlet valve that’s to the carburetor will close; this will prevent the Fuel Pump from pumping more fuel into the carburetor - like it should be doing. At this exact point, if there is any fuel left inside the pump chamber, that fuel becomes trapped. The diaphragm will then continue to let pressure flow to the diaphragm.

Since one side of the pump diaphragm has fuel that’s under pressure and the other side of the diaphragm is connected to the crankcase of the engine, if the diaphragm ends up splitting - which is a common failure - it can eventually leak fuel into the crankcase.

To draw the fuel through the lines, the Fuel Pump needs to create negative pressure. Nevertheless, the low pressure that’s between the pump and the fuel tank can eventually cause the fuel to vaporize in the supply line. This can end up with something called “fuel starvation” as the Fuel Pump causes the engine to stall - and I think that’s the worst possible thing that can happen to you if you’re just driving on the road.

So to just sum up this whole thing, make sure that you take care of your Fuel Pump considering it’s the most important part of your car. You’ve read about all of the things that can happen if you don’t take care of it .. so just do you and your wallet a favor, take care of it .. unless you have the engine that doesn’t need a fuel pump; make sure you take care of the other important parts of your car.