>>How to Diagnose a Fuel Pump Failure?

How to Diagnose a Fuel Pump Failure?

One of the most important parts of a car is a fuel pump. A car engine needs a regular flow of fuel regularly to keep its functionality running. That’s the job of a fuel pump, without that a car will be sitting in a car tank at a dormant state. So this is an obvious fact that if your car’s fuel pump is failing it’s a big problem. In this article I am going to explain how you can identify a bad fuel pump and what you can do to solve the issue, we will also cover the issues of fuel pump replacement and the replacement cost.

Types of Fuel Pump

The term ‘fuel pump’ is pretty much self-explanatory on its own. It is a pump that provides a regular flow of fuel into the car’s engine and all other necessary parts. It is usually located in between the fuel tank and engine. Normally it is located either inside the fuel tank of the car or somewhere at the fuel line at the bottom of the car. There are two types of fuel pump available in general. What type you use depends on the model and age of the car:

  • Mechanical
  • Electric


An old school pump that runs on the motion of the engine. It has a diaphragm mounted on the engine outside opening which expands and contracts to create a low-pressure system to pass fuel to the necessary parts. It is used in the cars that need carburetors.


A newer iteration of the fuel pump that is located inside of a fuel system. This type of fuel pumps uses electromagnetic motors to force the fuel into the necessary parts. This type of pump is usually used with cars that have the fuel injection system.

What causes a fuel pump failure?

When a fuel pump is partially or fully unable to pump fuel into the car’s necessary parts it is considered to be a fuel pump failure. If you are going to diagnose a failure the first thing you need to know is the reasons that cause the symptoms of a bad fuel pump. There are several reasons that cause bad fuel pump symptoms. Some of them are:

Broken Wiring:

One of the most common reasons for a failure is broken or faulty wiring. Faulty wiring in a car’s fuel pump system interrupts the fuel flow to the fuel pump from the relay. Corroded, loose melted or burnt wires or connectors and poor electrical grounding can restrict the voltage flow from the relay to the fuel pump. This affects the functionality and causes failure.

Clogged fuel filter:

The pickup strainers or the filters presented in the fuel pump can be clogged by the use of either dirty fuel or the presence of contaminants. This can cause low pressure and low peak flow of fuel in the pumping system, especially the filter that weakens the fuel pump. Clogged filters are normally associated with damaged fuel line connectors or cracked hoses or kinked fuel line that causes serious fuel leakage. These can create vacuum leaks which disrupt the air-fuel ratio thus making the engine run lean. This is also another reason that causes bad symptoms.

Driving with a low fuel level:

Fuel pump durability depends on the lubrication and cooling rate provided by the fuel. So if anyone regularly runs the vehicle on low gas tank the fuel tank gets more heated and this causes the fuel pump to overheat and become dry. This may cause serious damage.

How to diagnose a failure?

Now the most important question is how you can understand if you need a fuel pump replacement? The question is tricky but the answer is actually quite simple if you know the right signs to follow. There are ways to indicate a faulty fuel pump. There are many signs of a bad fuel pump which can indicate the need for a fuel pump replacement. Here we are discussing some of the signs that indicate that your fuel pump needs replacement:

Reduced fuel efficiency:

If there is a problem in your fuel pumps than the most notable change you will see is that you will have reduced fuel efficiency. Your car will use more fuel than its regular consumption. There are other reasons as well which can cause this. But the change caused by fuel pump failure will be more significant than other reasons. The fuel pump has a relief valve that controls the fuel flow but in a defective fuel pump, they have reduced efficiency which causes more fuel flow to the engine. Thus causing a decreased mileage. In laymen term, if your car used to have a decent mileage but suddenly became a gas hog than it is a good symptom of failure.

Black smoke:

When you are looking for signs of a bad fuel pump the most common sign that you should look for is black smoke coming from the vehicle, especially from the exhaust pipeline. It is caused by the leaked half burnt oil. Normally the smoke comes out of the pipe is grey or whitish but if your fuel pump is problematic then there will be black smoke in the pipeline.

Strange noises from the engine:

Another common sign of a failure is high pitched screeching sounds coming out of the engine. This is an early sign of failure. Though similar sound also occurs in a new engine it disappears after a while. Even when you are driving it is normal to have a humming sound from the fuel pump. But with a broken fuel pump it will get cranky over time and will produce these noises. The sound may be a loud whine or howl or a high pitched humming sound. These sounds are the signs of a bad fuel pump.

The engine will sputter:

One of the most common signs of a bad fuel pump is a sputtering engine. When driving on the highway and you are speeding up your car will sputter or begin to jerk. This will occur after several hours of the smooth, normal driving engine will continue to misfire again and again. Though many people blame low-quality fuel for it it is most likely another sign of a bad fuel pump. When a defective fuel pump can’t supply enough fuel to the engine then it will only receive air which will cause some power strokes to miss and thus forcing the engine to sputter and jerk. In the early stages, the sputtering will last a few minutes but the time will increase with time.

The engine isn’t starting:

If someone manages to ignore all the signs of a bad fuel pump the engine will fail completely. Once the fuel pump has failed completely it has lost the ability pump oil into the engine or any other part of the car, as a result, your car won’t start; you may hear the engine spark plug clicking but the engine won’t start. There are many other reasons for this same problem but you can easily confirm it with a fuel pressure gauge test in your car.

Sudden engine Surge:

Another problem caused by the failed fuel pump is sudden engine surge which is the opposite of sputtering or misfiring. You are driving at a consistent speed and suddenly your car surges ahead as if you have stepped on the gas. This is caused because the fuel pump has irregular current in its motor. It means that it does not have enough power to maintain the proper pressure through the fuel line.

Abrupt loss of power:

Another notable symptom of a failure is the loss of power of the Car. When you are trying to accelerate from a stop or trying to drive uphill or a rough terrain the engine loses power. Or in normal terms, the car does not feel as strong as it should be. This happens because it cannot pump enough fuel as effectively as it should have. The old or failing fuel pump cannot keep up with the engine’s extra demand of fuel when driving uphill or pull a road, so it leads to power loss under stressful condition. Eventually, the power loss will occur even in a normal situation. As you are accelerating from a sudden or regular stop your engine will start to sputter. The car will shudder and feel like it is going to stall but after a while, it will get back to normal.

Rising Temperature:

A failed fuel pump will have a significant effect on the car’s temperature. Always keep an eye on the temperature gauge. The car temperature will rise abruptly with occasional engine stalls. If it happens on a regular basis, it is a sign of failing.

Fuel pressure gauge:

Check the car’s fuel pressure gauge, if the pressure gauge doesn’t indicate enough pressure as it should then there is a problem. It is the most direct way to diagnose a failure.

Leaking fuel:

If the fuel pump fails the car will constantly leak fuel. The alarming fact is this problem does not easily spot-able as the previous one and you actually need a help from an expert to understanding the leakage but you will be able to spot a leakage by the increase of the gas your tank needs.

Blackened Spark plug:

A very notable symptom of a failure is seen on the cars spark plug. If the fuel pump is failing the spark plug will have a blackened layer of dust like a deposit.

Weak acceleration:

The car will have a very weak acceleration if the electric fuel pump is failing because acceleration requires more fuel than usual. But a faulty fuel pump cannot provide the required fuel thus weakening the acceleration.

Weak Decelerating:

A failing fuel pump can also cause trouble when the car decelerates. Because of a broken fuel pump, the engine gets an excessive gasoline build up and this will cause the driver to get a hard time adjusting the speed especially when running fast.

Extended Engine cranking time:

In order to cool down an engine, the maximum amount of fuel is sent back to the fuel tank. There is a valve that controls this action, but if the fuel pump fails the valve gets close prematurely and fuel cannot get back to the tank this causes the crank to stutter when starting the vehicle.

Gasoline in the vacuum hose:

If the fuel pump fails there will be a significant amount of gasoline leakage through the vacuum hose of the car after it is switched on.

What Precautions should I take to avoid a failure?

If you want to avoid a fuel pump failure there are some common precaution advised by the experts around the globe. Some of them are listed below:

  • Purchase high-quality fuel
  • Don’t purchase fuel when the tanker is filling up
  • Avoid driving with an empty tank
  • Clean it regularly
  • When replacing a fuel pump make sure to clean the fuel tank as well

What to do when I have found the bad symptoms?

If you have found at least one or more bad symptoms in your car,  you need a replacement. But before you do that there are some things needed to be checked before by the repair shop. Here we will tell you what they are:

  • First, check the fuel pump by starting the car.
  • Evaluate the fuel pressure with the fuel pressure gauge
  • Using a micrometer Check fuses
  • Inspect fuel pump relay
  • Check fuel pump’s power and codes.

Take Your Vehicle to an Auto Parts Store

After identifying the issues and checking your car it is better advised to take your vehicle to an auto parts store and consult with an Auto Mechanic. Some of the signs caused by a bad fuel pump can also be caused by other mechanical problems as well. So, the repair shop or the technician will perform some tests to determine the exact reason or the problem. After they found the problem if no other sources seem likely the shop will confirm the fuel pump diagnostics with a series of procedure.

For most shops, the series of procedure is the same with a minor difference in one or two processes. First, they will check the fuses of the car’s electrical system, especially the fuses that are used in the fuel system. If the fuses are damaged then fixing those will change the problem. Then the mechanic will check the voltage on the pump using a multi-meter to determine if the problem is in the pump itself. After that, there is some other test that they will perform after that and finally, they will tell you the cost for replacing the fuel pump or fixing it. After that, they will take the necessary steps to fix your car.

Your fuel pump is an important part of your car. But like any other device, the eventually wear out after a thousand miles of use. So if you find any of the symptoms of a bad fuel pump, time to take your car to a good repair shop.

By |2018-12-11T02:05:28+00:00December 10th, 2018|Blog|0 Comments

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