Fuel pump doesn’t work after replacement? This is why

The fuel pump plays a crucial role in drawing fuel from the fuel tank via the fuel line to the fuel injector or carburetor through the fuel filter and finally to the cylinder chamber for combustion.

So, have you just replaced a bad fuel pump with a new one but it is still not working? If yes, then it could be because of multiple reasons, including correct installation, bad wiring, and much more.

In this article, we will tell you why your fuel pump is not working after replacement and the solution to each problem.

Why is the fuel pump not working after replacement?

If you are experiencing problems with your fuel pump after replacing it, then the problem could be a result of several issues as discussed below.

The fuel pump was not installed correctly

One of the reasons why your fuel pump is not working after the replacement is because it was not installed properly. The fuel pump is a very sensitive component that only works if installed properly.

Some of the signs that indicate the fuel pump was not installed correctly include engine start difficulty, engine stalling, and rough idling.

Bad wiring

Another reason why your fuel pump is not working is because of bad wiring. If your fuel pump starts to display inconsistent gauge reading, then your fuel pump has a wiring problem.

Your fuel pump will only work correctly if the wiring is done right as recommended by the manufacturer.

The fuel pump is incompatible with your car

If you lack proper knowledge about fuel pumps, you may end up installing a fuel pump that is not compatible with your car’s make and model.

Sometimes even fuel pumps from the same car model are not compatible with each other. Therefore, if your fuel pump is not working, take it to a reputable mechanic to check if it is compatible with your car model.

Common signs of fuel pump incompatibly include engine start difficulty, rough idling, and engine stalling.

Faulty fuel pump

Your fuel pump could also not be working because it is faulty. This is most common to fuel pumps that were not stored properly. If your car is experiencing engine start difficulty or engine stalling, then it could be a result of a faulty fuel pump.

Common problems you are likely to get after changing the fuel pump

The reason why people change their car fuel pumps is that they want the vehicle to run smoothly without any fuel pump problems.

Unfortunately, that is not usually the case. In this section, we will discuss the common problems you are likely to experience after replacing your fuel pump.

Engine start difficulty

One of the common problems you are likely to experience after changing the fuel pump is difficulty in starting the engine mostly due to lack of fuel pressure.

When your vehicle stays for a while, you will realize that it cranks for a few seconds before starting. The major problem, in this case, is the lack of fuel pressure. Fixing this problem involves checking the fuel line for any loose connection or damages.

Incorrect fuel gauge reading

Another problem you are likely to experience after changing the fuel pump is incorrect fuel gauge reading. This problem usually occurs if there is a problem with the sending unit, a device that tells the fuel gauge how much fuel is in the tank.

If this device is not working, then the fuel gauge on your new fuel pump will give an incorrect reading. The solution to this problem is to take it to the mechanic to have it checked.

If the problem is on the sending unit, they can clean or replace it. If the problem is with the fuel pressure gauge, then the mechanic can replace or repair it.

The fuel gauge not working properly

You may also realize that your fuel gauge is not working properly after replacing your fuel pump. In this case, the problem usually lies with the fuel sender unit which sends a signal to the gauge to determine how much fuel is in the tank.

Another reason why it is not working properly is if there is an issue with the wiring between the sender unit and the gauge. The solution to this problem is checking if the sender unit in the oil tanks is connected correctly, checking the wiring system, or replacing the fuel gauge, if damaged.

Rough idling

Rough idling usually occurs when the car is not getting enough fuel mostly due to improper installation. Changes in fuel pressure, especially a sudden drop could result in rough idling.

A fuel pump that does not suit your car could also result in rough idling. You can fix this problem by ensuring the fuel pump is installed properly and is also compatible with your car.

How long does it take for the new fuel pump to start working?

After replacing your car fuel pump, it will take between 2-3 hours for it to start working. You have to give the new pump ample time to send fuel with the right pressure to the engine.

Do I have to prime my fuel pump?

It depends on your car model and year of manufacture. If you are replacing a fuel pump for an older car model, (below 2005), then you may have to prime the fuel pump to allow a smooth flow of fuel.

On the other hand, if you have a new car model, 2010 and above, you don’t need to prime the new fuel pump after installing it because the fuel pump will draw enough of a vacuum to prime itself.

How do I prime my fuel pump after replacing it?

Priming the fuel tank after replacing it is easy. Below are the simple steps to follow.

-Fill the fuel tank
-Turn the ignition key to the ON position
-Move the engine Stop/Run switch to the RUN position
-Allow the fuel pump to run until it stops (about 5 seconds)
-Move the engine stop/run switch to the STOP position
-Repeat this process 3-4 times.


If your fuel pump is not working after replacement, don’t panic. Instead, take your car to a trusted and experienced mechanic for a checkup.

There are multiple reasons why your fuel pump is not working including incorrect installation, bad wiring, incompatibility, and much more. Your mechanic will determine where the problem is and fix it.

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