What is a Fuel Pump?- 7 Signs of a Bad Fuel Pump

What is a Fuel Pump?

The fuel pump sends fuel from the gas tank to the engine. In modern cars, fuel pumps are usually electrically powered and located directly in or on the fuel tank. The ease and cost of replacement depends on the car’s design, and it should be undertaken only after determining the problem isn’t electrical or related to the fuel lines.

Modern vehicles with an internal combustion engine are equipped with an electric fuel pump. Most cars have an in-tank pump mounted within the fuel tank, although some have an inline pump located between the gas tank and the engine.

By understanding the basic process of the fuel pump, you’ll have a better understanding of what happens when a fuel pump goes out—and how to recognize when it’s happening.

  1. Fuel in your tank is drawn up through a line that heads toward the engine.  If your fuel pump is electric, it’s operated by a small motor that draws the fuel sitting in your gas tank up through a fuel line. In older vehicles with mechanical fuel pumps, the pump moves as your camshaft spins and fuel is drawn through a line using suction.
  2. Fuel travels through the fuel line and toward the carburetor or the cylinder. Depending on your engine makeup, your fuel line will go directly to the cylinder or will have a pit stop elsewhere.
  3. Air is injected into the fuel to create a mixture.
    • In carbureted engines, fuel is injected with air and forms a mixture in the carburetor. Then, the mixture heads toward the cylinder.
    • In a fuel-injected engine, fuel and air don’t mix until they reach the cylinder. (Most modern vehicles have a fuel-injection system.)
  4. The fuel combusts, creating energy. Within your cylinder, the ignited fuel and air mixture is compressed by the piston. As the piston moves and the fuel mixture becomes more compressed, a spark plug provides a spark to ignite the mixture and the piston fires.
  5. The released energy now powers the crankshaft. You’re officially on the move. That fuel has successfully moved your car further down the road and is being expelled as exhaust after its useful life.

That five-step process has dozens of smaller steps in between, but it all starts at the fuel pump. If the fuel you’ve put into your tank can’t make its way to the engine to be mixed with air, steps two through five aren’t happening, and you’re not making progress down the road.

What is a Fuel Pump

Types of Fuel Pumps

There are basically three types of fuel pump available in the market, each of them is discussed below:

1. Mechanical Fuel Pump

These are basically the low-pressure type of fuel pumps, sometimes also used for high pressure, whose main work is to transfer the fuel from the tank to the fuel bowl of the spark-ignition engine.

A mechanical fuel pump is driven by the camshaft, or by a special shaft driven by the crankshaft. As the shaft turns, a cam passes under a pivoted lever and forces it up at one end. The other end of the lever, which is linked loosely to a rubber diaphragm forming the floor of a chamber in the pump, goes down and pulls the diaphragm with it.

When the lever pulls the diaphragm down, it creates suction that draws fuel along the fuel pipe into the pump through a one-way valve. As the revolving cam turns further, so that it no longer presses on the lever, the lever is moved back by a return spring, relaxing its pull on the diaphragm.

The loosely linked lever does not push the diaphragm up, but there is a return spring that pushes against it. The diaphragm can move up only by expelling petrol from the chamber. The petrol cannot go back through the first one-way valve, so it goes out through another one leading to the carburetor. The carburetor admits petrol only as it needs it, through the needle valve in its float chamber.

The mechanical fuel pump consists of two kinds of pumps; i.e.; diaphragm-type fuel pump and plunger-type fuel pump.

Diaphragm Type Fuel Pump

The diaphragm type fuel pump is basically a positive displacement pump that sucks the fuel by expanding and contracting the motion of the diaphragm. The pump body consists of inlet and outlet check valves, which are one-way valves. As the diaphragm contracts, the pressure inside the pump becomes lower than the atmospheric pressure, and the fuel gets sucked through the inlet valve.

And, as the diaphragm expands, the fuel inside the pump is pushed out through the outlet valve. The expansion and contraction movement of the diaphragm is controlled by a lever-actuated by an eccentric cam motion. This eccentric cam is connected to the crankshaft of the engine through proper gearing arrangement.

Plunger Type Fuel Pump

The plunger-type fuel pump is also a positive displacement pump that sucks and delivers the fuel with the help of the reciprocating motion of the plunger. The plunger is enclosed inside a cylinder and one side of the plunger is connected with a push rod which further connects the camshaft.

The valves are mounted on the end of the cylinder. As the plunger moves backward the fuel gets sucked into the cylinder and with the forward motion of the plunger, fuel gets delivered out of the cylinder.

Although the pressure of the fuel supplied from the mechanical pumps is constant it requires proper maintenance because of lots of moving parts. These pumps become obsolete nowadays because the vehicles are changed their injection system from carburetor to fuel injection system.

2. Electric Fuel Pump

These types of fuel pumps are generally used in fuel injection systems, which is the essential part of modern motor vehicles. It creates high pressure to deliver the fuel out of the pump. This high pressure may cause the fuel to ignite inside the pump itself and be a reason for the explosion. Thus, for safety purposes, the electric fuel pump is kept far from the engine and more specifically, it should be kept inside the fuel tank.

The current to operate the fuel pump is supplied by the battery of the vehicle. An electronic control unit (ECU) is also available there which properly controls the output pressure and volume of the fuel and in addition, it also meters the incoming fuel from the tank. The ECU helps the vehicle to save fuel and hence gives better mileage and power.

How an electric pump works

An electric pump has a similar diaphragm mechanism; it is worked by a rod that is drawn into a solenoid switch until it opens a set of contacts to turn off the current.

The solenoid attracts an iron rod that pulls the diaphragm down, drawing petrol into the chamber. At the end of its travel, the iron rod forces apart a set of contacts, breaking the current to the electromagnet and relaxing the pull on the diaphragm.

When the diaphragm return spring raises the diaphragm, it also pulls the rod away from the contacts; they then close so that the solenoid pulls the rod and diaphragm down again.

3. High-Pressure Fuel Pump

These types of fuel pumps are generally used for the direct injection of fuel into the combustion chamber, specifically, in combustion ignition engines. These types of pumps work above 200 Pascals. To handle such a high pressure, these pump systems are made complex and sturdy.

The general high-pressure pump system having flow rails, metering units, distributing units, etc., helps the pump to supply the fuel into the combustion chamber without any wastage or over-fueling.

Signs Your Fuel Pump Is Going Bad

Trying to figure out how to tell if a fuel pump is bad has a few tricks. The common signs of a bad fuel pump include: 

Whining noise comes from the fuel tank area when the engine is running.

  • Stalling that will restart after several minutes.
  • Trouble starting the car.
  • Lack of power.
  • Long cranking time.

Whining Noise

A whining noise from the tank often is a precursor to loss of pressure or total failure. It can sometimes last with a bad fuel pump sounds for hours, weeks, or indefinitely. If the pump is whining, keep a close eye on it. 

Car Is Stalling

If your car is stalling and it will restart after sitting for a bit, the fuel pump may be overheating. The cause is often from being operated with low fuel in the tank frequently, since the gas actually cools the pump too. Odds are that it will completely fail soon. 

Difficult To Start Your Car

Difficulty starting the car can be an indication that the pump has quit altogether or has extremely low pressure, and lack of power when you’re driving is also a symptom of bad fuel pump that goes hand in hand. 

Long Cranking Time

Long cranking time usually indicates that a fuel pump won’t hold positive pressure in the fuel line with the engine off. The fuel has bled back to the tank, and cycling the key is necessary to re-prime the line before the car will fire up.

How Long Do Fuel Pumps Last?

The fuel pump is your vehicle’s unsung hero. It takes gas from the gas tank and sends it to the engine so your car, truck, or SUV can start and run. Your vehicle’s fuel pump should last at least 100,000 miles or more.

There is really no reason to preemptively replace the fuel pump before 100,000 miles. Fuel pumps have been known to last for over 200,000 miles in some cases. After 100,000 miles, the failure of the pump is likely enough that if you are replacing a major part in the fuel system nearby, it may be advantageous to replace it at the same time.

When should the fuel pump be replaced?

It is usually unnecessary to preemptively replace the fuel pump, but if there is another service being performed on the vehicle that involves removing the gas tank, and the current fuel pump has been running for over 100,000 miles, then replacing it could save money and time in the long run.

If the fuel pump seems to be surging and then not delivering enough fuel, get it inspected by a qualified mechanic right away. The fuel system is necessary to keep the car running and a poorly maintained fuel system is downright hazardous.

How To Replace a Fuel Pump?

If your fuel pump is not pumping enough fuel to keep up with the engine, it may need to be replaced. This can be completed in 12 seamless steps.

If your fuel pump is not delivering enough fuel pressure to meet specifications or not pumping enough fuel to keep up with the engine, it may need to be replaced.

This can be completed in 12 seamless steps; however, it is recommended to have an assistant to facilitate the process.

  1. Park the vehicle on a firm, level surface and set the parking brake.
  2. Find the fuel pump, which on most vehicles is in the fuel tank. Once located, open the fuel cap and have an assistant turn the key to the ON position while you listen at the filler opening. The fuel pump will hum for two to three seconds, if working properly. If no sound is made, replacing the pump may be necessary.
  3. Find and verify the fuel pump fuse and relay.
  4. If the fuse is blown, replace it with a fuse of the same amperage. Check fuel pump operation. If the fuel pump works, your job is done.
  5. If the fuse and relay are functional, check for power and ground at the fuel pump. Removing the fuel tank or the back seat may be necessary. If there is power and ground at the pump, then the pump is faulty.
  6. Relieve the fuel system pressure. Disconnect the negative battery cable.
  7. Siphon or drain as much fuel as possible from the fuel tank. Disconnect the filler tube hose and the electrical connection to the pump.
  8. Support the fuel tank with a jack and a block of wood. Remove any retaining straps or bolts holding the tank to the frame. Lower the tank.
  9. Disconnect the fuel lines and remove the fuel pump from the tank.
  10. Compare the new fuel pump with the original to verify that you have the correct part. Install the new fuel pump.
  11. Connect the fuel lines to the pump. Lift the fuel tank up and install the retaining strap. Reconnect the filler tube hose and the electrical connector.
  12. Reconnect the negative battery cable. Fill the tank with gas. Conduct a road test to confirm a successful repair.

Fuel Pump Replacement Cost

The average cost for a fuel pump replacement is between $220 and $1,062, depending on vehicle and age. Labor costs are estimated between $124 and $260, while parts are priced between $95 and $854. Estimates do not include taxes and fees.

If you are replacing the fuel pump yourself, beyond this it is just the cost of your time. Generally speaking, replacing a fuel pump is considered an intermediate-level task.

If you decide to go with a professional, you may be looking at a cost of between $400 and $600 to replace a bad fuel pump. You can search through our Preferred Shops in your area for a mechanic that can help with the fuel pump repair. Expect the actual replacement to take between 1 to 6 hours, depending on the expertise of the mechanic and the tools they happen to have on hand.

Whether you do the job yourself or have a professional do it, make sure that the fuel tank is properly cleaned of all contaminants, as years of fuel sediment can build up in the bottom of the fuel tank.

How To Start a Car with A Bad Fuel Pump?

There are a few methods to start a car with a failing fuel pump. These are simple suggestions to try even if you don’t possess much mechanical ability. Professional mechanics will remind you that this is a temporary solution to a severe problem that is best not to ignore.

  • Fuel Pressure Gauge – Attaching a fuel pressure gauge directly onto the engine will allow the car to start and drive. A fuel pressure gauge usually is in the $40 price range and is a handy tool to have available.
  • Manual Pressure – Using pressure to assist the fuel through the lines is another simple technique to start the car.
  • Engine Heat – The engine overheating due to a faulty fuel pump is possible, but if the car is shut off and cooled, the low temperature can also cause the pump to stall. Maintaining a consistent heat to the engine can allow you to drive the car far enough to reach a repair shop.