6 Symptoms of a Bad Fuel Pump

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A faulty fuel pump will cause engine performance issues and in many cases it will even leave you stranded. That is why it is important to recognize the symptoms of a bad fuel pump or relay before it actually fails.

An example of a typical fuel pump

The fuel pump is located in the fuel tank of most modern vehicles. It is powered by electricity and its function is to move the fuel from the tank to the engine. Most fuel pumps are classified positive displacement pumps. These pumps utilize rotating gears to accelerate the fuel from the pump inlet to the pump outlet. Over time these pumps can wear out. Seals can go bad creating internal leakage reducing fluid flow. A faulty or shorted fuel pump relay will also cause pump failure. A fuel pump relay provides current to the fuel pump when activated.

The fuel filter is an essential part of the fuel system. The fuel filter covers the pump inlet. Its function is it stop contaminates in the gasoline from entering the fuel system. Generally speaking a fuel filter is rated to around 100 microns. This means it should stop any particles over 0.0039in from entering the pump.

Another important component of the fuel pump is the pressure regulator. The pump will create excess flow and pressure. The pressure regulator will limit the fuel pumps output pressure and return excess fuel back to the gas tank. Fuel pressure is usually in the 35 -65 psi range for modern vehicles.

1. Whining Noise from the Fuel Tank

The first and most common symptom of a bad fuel pump that you should notice is a whining noise from the gas tank. This symptom can almost always be attributed to the fuel pump. A whining fuel pump is a sign that the fuel pump is wearing out and should be replaced. Keep in mind that a normal functioning fuel pump will let off a quiet humming sound. This is because of the electric motor. The whining noise is very different from this humming noise.

2. Poor Performance Under Load

Vehicles require the most fuel when accelerating, carrying heavy loads, and traveling uphill. During these conditions, a failing fuel pump could cause the engine to shutdown. This is because the fuel pump is not able to keep up with the engine’s demands. If you experience the engine shutting down or unable to maintain power, it may be because of the fuel pump.

3. Low Gas Mileage

Low gas mileage can be caused by many things other than the fuel pump, but the fuel pump could still cause poor gas mileage. If the fuel pump pressure regulator valve was not bypassing enough of the excess fuel flow, that excess fuel will get into the fuel system and eventually will be ignited or exit through the exhaust.

4. Vehicle will not Start

If your car doesn’t start this could be because of a faulty fuel pump or fuel pump relay. The engine won’t be able to start without pressurized fuel in the fuel system. In this case the pump could be failing completely and not outputting any fuel, or it may just be not outputting enough fuel for the engine to start. Either way you won’t be able to run your engine consistently.

Also, the fuel pump relay could be faulty. A faulty relay will not send current to the electric motors which spin the gears on the fuel pump. This will prohibit the fuel pump from working even if the fuel pump is fine.

A few symptoms of a bad pump relay include:

  1. Engine Stalls – If the engine suddenly stalls or cuts out with no warning, this could be fuel pump relay related.
  2. Engine Won’t Start – A completely failed fuel pump will not allow the pump to work causing the engine to not start as discussed above.
  3. No noise from the Fuel Pump – Generally even a faulty or failing fuel pump will make noise when it is running. If your fuel pump is not making any noise when it should be running, you may have a faulty relay.

There are many issues that can cause a vehicle not to start such as a dead battery, weak connection between battery terminals, faulty starter motor, belts, etc. If your vehicle doesn’t start be sure to either have it inspected by a professional so that they can determine the root cause.

5. Engine Stall at High Temperatures

Engine stalls at high temperatures is also one of the symptoms of a bad fuel pump. If you experience the engine heat rising and the vehicle stalling this usually is sign of a deteriorating fuel pump. The fuel pump should be replaced soon, before it can cause other problems in the vehicle

6. Sudden Increase in Engine Speed

If you are cruising at a steady pace and make no adjustments to the gas pedal, but the engine speed surges, this is another one of the symptoms of a bad fuel pump. This fault can be dangerous and down right scary if it happens at the wrong time. This problem is usually caused by an irregular resistance in the pump. If you experience engine surging, be sure to investigate and replace the fuel pump.

How to Maintain a Fuel Pump

With proper care, it is not uncommon for fuel pumps to last the life of a vehicle. Most fuel pumps are designed to last 50,000 miles, but with care that mileage can be much longer. Keeping your gas tank above 1/4 of a tank will do wonders for your fuel pump filter and fuel pump. This is because under 1/4 of a tank, the fuel pump starts to suck up extra particles and contaminates that lie at the bottom of the gas tank. These particles can clog the filter or pass through the filter and damage the pump internals.

Keeping the tank above 1/4 full will also allow the electric motor that runs the fuel pump to be immersed in the gasoline. This will allow the motor to transfer heat the gasoline and not overheat itself.

If you do need to buy a new fuel filter, be sure to check out these fuel filters from Four Wheel Parts here.