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What is a Fuel Pump?

By Katharine Swan
Updated May 23, 2024
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Because the fuel tank is located on the opposite end of the car from the engine, a fuel pump is required to draw the gas toward the engine. There are two kinds: mechanical, which were used in carbureted cars, and electric, which is used in cars with electronic fuel injection.

A carburetor is a fuel delivery mechanism that makes use of the simple principle of vacuum in order to deliver fuel to the engine. The same vacuum that draws the air-fuel mixture into the engine also draws fuel along the lines toward the engine. However, additional help is necessary, so carbureted engines have a mechanical fuel pump. This runs off of the engine's rotation; as a result, in a carbureted car, it is located alongside the engine.

Electronic fuel injection is a delivery system that squirts a fine mist of fuel into the combustion chambers of the engine. A computer controls the system, closely monitoring factors such as the position of the throttle, the air-fuel ratio, and the contents of the exhaust. Because the system does not use a pre-existing force, such as vacuum, to draw the fuel along the lines, the fuel pump must be located at the source — that is, inside or next to the fuel tank itself. The pump is electronic, meaning that it is powered and controlled electronically. Sometimes, its operation can be identified by a soft, steady humming sound coming from the rear of the car.

Fuel pump failure is not uncommon, particularly in cars with electronic fuel injection. Usually, when it fails, a car will simply sputter and die, and will not restart. Essentially, a car with this failure will act like it is out of gas, even when there is gas in the tank. Fuel pump failure can be verified by checking the fuel delivery end of the system; if no fuel is being delivered to the engine, the fuel pump has most likely failed.

Replacing an electronic fuel pump can be tricky business. In some cars, it is located in an area that is easy to access from underneath the car. Other cars have an access panel in the interior of the car that can be removed to reach the fuel pump. Still other cars require the fuel tank to be siphoned and removed, or dropped, before the pump can be accessed. The latter type of car usually makes for the most laborious replacement job.

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Discussion Comments
By anon218961 — On Oct 01, 2011

@Sabadie: Pumps are made to provide head pressure after the pump, not pull liquids in suction before. I'm a mechanical engineer. The pump should go by/in the tank.

By anon175858 — On May 13, 2011

what drives the fuel pumps? anyone please answer. Thanks in advance.

By anon100888 — On Aug 01, 2010

what was the lubricant for the FIP?

By sabadie — On Jun 05, 2010

I have a Plymouth voyager 1995 car.

The fuel pump isn't working (the fuel pump is located in-tank).

So, the question is: Can I install an external fuel pump connected in engine intake pipe without removing the original fuel pump? Thanks

By anon86570 — On May 25, 2010

my pump is pumping gas, but I hooked a fuel pressure gauge into the injection tap and it's reading 0. My pump only comes on when the ignition system is in the start position and does not run while in the regular on position. Could that be an electrical problem? Or is it the pump?

By anon61471 — On Jan 20, 2010

can an electric fuel pump go if you don't use your car too much? The car just has 3000 km and it is a toyota.

By anon39208 — On Jul 30, 2009

has electric fuel pump any thing to do with efficiency of vehicle when its getting heated up?

By LoveLearn — On Jul 22, 2009

"Because the fuel tank is located on the opposite end of the car from the engine, a fuel pump is required to draw the gas toward the engine." The word "draw" suggests that fuel pumps generally produce a lower than atmospheric pressure (about 14.7 psi) to move fuel from the tank toward the engine. That description was true of engine-mounted mechanical fuel pumps used years ago on carburetor-fueled engines. But it is *not* true of most injector-fueled engines.

"Fuel pump failure can be verified by checking the fuel delivery end of the system -- if no fuel is being delivered to the engine, the fuel pump has most likely failed."

That over-simplifies fuel pump testing so much that if many injection-fueled engine owners follow it, they will be frustrated by not discovering their engine's performance failure cause.

The following actual example is typical of many automotive fuel injection design strategies. An in-tank electric fuel pump is specified to be capable of delivering 65 psi minimum and 84 psi maximum to the second fuel filter. The first fuel filter is a mesh screen enclosing the pump's intake opening. After the second fuel filter, a pressure-limiter regulator returns fuel to the tank through a second fuel line if pressure rises above that devices specified range of 34 psi minimum and 40 psi maximum. Also, the pump has a specified minimum flow volume at some test pressure, commonly the regulator's minimum pressure range value.

Through years of wear, a pump's pressure making capability and flow volume capability at minimum useful pressures *slowly* declines. During that slow capability decline, no engine performance characteristics are observed until that decline begins dipping into the injector system's demand curves under various operating conditions. So initial performance loss, when it actually appears, only slowly degrades engine performance under the most demanding circumstances. But as the pump continues its performance decline, slowly engine performance erodes. Perhaps the pump gets so bad that it can only deliver 25 psi. The return regulator is no longer opened, so fuel is not being returned to the tank and not being repeatedly filtered. Injection squirts are so weak that they don't atomize well and delivered volume during the brief injector opening triggered by the engine management computer is so reduced that the engine can barely run. Yes, the pump still pumps. The ignition system is still performing well. The air mass flow sensor is performing well. The idle air metering stepper-motor controlled valve is still following the engine control computer's instructions. But it can't run well due to miserably low pressure at the injectors.

Look up your engine's fuel pump specified pressure range and flow at specified pressure minimum and test for those values. 25 psi might seem like a lot while testing with a thumb over the filter's output tube, yet it might not be enough to enable that engine's fuel system to perform its design task.

By lebodu — On Jun 23, 2008

Is it common for electric fuel pump to keep failing ?

By anon3363 — On Aug 25, 2007

Is it common for electric fuel pump to keep failing ?

What could be responsible for this repeated failures ?

What is the solution ?

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