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How Does a Fuel Pump Work?

Video transcription

The next question is about fuel pumps and how they work. The older style fuel pump that is no longer used is called a mechanical fuel pump. This fuel pump is actuated by the camshaft or the push rod coming off the camshaft. An automotive camshaft has a special assentric that pushes up on the rocker arm that you can't see that is inside the engine and when that pushes up it pulls down on a diaphragm. That diaphragm creates a vacuum in the fuel line coming from the fuel tank and then that vacuum allows that line to become filled with fuel and actually draws fuel up into the inlet side of the pump and you can actually see the fuel inside the what we call the fuel bowl on the fuel pump right here. There is also a filter screen inside there. Then once that diaphragm releases that fuel goes up inside the chamber itself and actually goes through a check valve and a check valve is a one way valve, lets the fuel go into that valve and then once the pressure is released on the rocker arm the diaphragm comes back up and it pushes fuel out of the outlet and the outlet comes out through this line right here and goes in the carburetor and fills the fuel ball so that rocker arm is constantly pumping and push, forcing fuel up to the carburetor. Now what happens obviously is that the fuel pump has a much higher capacity to pump and you are actually going to pump more gasoline than the carburetor needs. So the carburetor has a float system inside that can actually shut off the fuel and when it shuts off the fuel when the bowl is full it is adjusted by a float inside, the fuel pump has to idle. So there is a little link in the rock around that just allows the rocker to go up and down and when there is liquid up against the diaphragm you want to remember that liquid is not compressible so once it is in a closed area you can't compress a liquid so the fuel pump just sits there and idles. That's the old style mechanical fuel pumps. The new style cars all use electric fuel pumps. The fuel pumps are located in the tank, they are not attached to the engine. Inside the fuel tank there is also a filter sock inside the fuel tank. It is a big deal on a newer car because if your fuel pump fails you are going to have to drop the tank. You are going to get towed in and you are not going to be able to fix it by the road side. This car here theoretically if I had a fuel pump fail and I had another fuel pump that I carried with me because this is a 37 vintage vehicle right here I could just with some simple hand tools actually replace this fuel pump at the road side. With the electric pump that is not going to be possible. The other thing to remember that the biggest cause of electric fuel pump failure is to let your fuel tank run down low that's why I say and always recommend keep your fuel tank at least half full. By doing that the fuel cools that electric fuel pump. That electric fuel pump runs submerged in fuel. Now some people are going to say wo isn't that a fire hazard isn't there going to be sparks but actually you're not going to get ignition if the fuel pump is completely submerged. I have really never heard of any case where a fuel pump has ignited from other than a car being in a collision so those are electric fuel pumps. There are some after market electric fuel pumps you could add to cars like these, quite often that's done because of the lower read vapor pressure of the lower fuels some of these cars tend to vapor lock where the fuel in the fuel line going to the carburetor will actually turn to vapor. You have to have liquid fuel delivered to the carburetor otherwise the carburetor cannot deliver atomized fuel into the intake system to cause the engine to run. So again sometimes electric fuel pumps are added to the system to keep the fuel circulating, to keep it cool on hot summer days so that you don't encounter vapor lock.

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