Can a Bad Fuel Pump Cause Misfire?

Naomi O'Colman

Can a Bad Fuel Pump Cause Misfire?

Can a Bad Fuel Pump Cause Misfire?

Your car’s fuel system is one of the most important parts of your vehicle and a failing fuel pump can affect the car’s performance. One of the common questions is that “Can a bad fuel pump cause misfire?“.

Well, a simple answer is yes. A bad fuel pump means that there isn’t enough pressure in the ignition chamber, which leads to misfiring.

What is a misfire?

If you lose power when you accelerate, it is probably a misfire. A misfire is when the ignition can not reach the cylinder and there is a noisy clicking sound from your exhaust pipe.

Can a bad fuel pump cause misfire?

When the fuel pump fails, the engine will not have the fuel it needs to run smoothly. The engine will not run and the car will turn off when you push the gas pedal. If the car is on for a long time, the engine will have bad performance because of a low supply of fuel.

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A misfire can cause poor acceleration, lack of power and it can cause your check engine light to come on. For most cars, your check engine light turns on when you have a misfire, so you can use that as a sign that your fuel pump is failing.

Symptoms of a bad fuel pump

If the fuel pump is going out, you might start to notice these symptoms:

  • Lack of power when you’re accelerating
  • Poor gas mileage
  • Hard time starting the engine
  • Engine clicks when it turns over
  • Misfire, which causes multiple cylinder misfires or random misfires.
  • You can hear a clicking noise from your exhaust system.

If you notice any of these symptoms, your car might have a bad fuel pump.

What problems does a bad fuel pump cause?

Apart from misfiring, a bad fuel pump can also cause your engine to run hot. If your engine is running too hot, it could cause the engine to fail in the future and might even cause you a serious accident while you’re driving.

Besides engine-related issues, a weak fuel pump will affect fuel efficiency as well. A weak fuel pump will not produce enough pressure, which will make your car consume more fuel. This way you will spend more money on fuel, but you’ll also need to get a new fuel pump.

How to check if your fuel pump is bad?

In most cases, a bad fuel pump will make a buzzing noise when it runs. You can use this sound to check if the pump is running or not.

There are also diagnostic tests that you can do at home to figure out if your fuel pump is going out. One of these tests is the resistance test and the other one is the pressure test. The resistance test will show you the amount of pressure that your fuel pump is holding, and the pressure test will show you the amount of pressure that your fuel pump is putting on the system.

  • To do a resistance test, you need to connect a meter to the fuel line and then touch the point where the line connects to your fuel tank and measure it using a meter. If your gauge shows 1 bar then there is no problem at all. If your fuel pump is going bad, then you will measure around 10-20 bar.
  • To do a pressure test, you need to install a pressure gauge on the intake manifold and the clamping system then turn the key on.
  • When your engine starts after an ignition cycle, it will give you a reading of 0 to 1 bar of pressure (around 10-17 psi). If your gauge shows 15 to 20 psi then there is no problem at all. If your fuel pump goes bad, you will measure more than 20 bars of pressure.
  • If your fuel pump starts leaking, it might cause a misfire when it runs.
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Some of the common ways of fixing the problem at home are to replace or repair the fuel pump, replace seized or bad injectors or replace with used parts. If you want to replace the fuel pump, you can just buy a whole new unit or you can change the fuel pump by yourself. If you have never changed a fuel pump before, it would be better for you to take it to your mechanic and ask them to change the fuel pump for you.


So, can a bad fuel pump cause misfire? Yes, it can. A bad fuel pump means that the engine has less pressure than needed, which makes the car misfire. If you have a bad fuel pump and your car is misfiring, the best thing to do is to change your fuel pump as soon as possible so it will not cause any serious damage to your engine.