Common Problems After Changing Fuel Pump – Top 5 Issues

In this article, we are going to discuss the common problems after changing fuel pump.

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It’s not all sunshine and roses when you change your fuel pump. You have to be careful that the new fuel pump is compatible with your car, otherwise, it could end up causing more problems than it solves.

So before you panic and ask “Why is my fuel pump not working after being replaced?”, you may want to read this first.

Common Problems after Changing the Fuel Pump

Some car owners reported that the fuel pump is not working after being replaced. Moreover, others experienced a rough idling engine, hard start, or inconsistent fuel gauge readings. This could be a result of incorrect installation, incompatible aftermarket pumps, or a bad fuel sending unit.

Related: Is My Fuel Pump Bad? Top 10 Symptoms of a Bad Fuel Pump

We’ll explain each problem below, the causes, and how to fix them.

1. Engine runs roughly after a fuel pump change

As mentioned above, some may complain that their vehicle runs or idles roughly after replacing the fuel pump. This problem usually exists because the engine is being starved of fuel. Well, most of you would eliminate that assumption because you just had a new fuel pump installed. But we’ll explain below.


If your car runs or idles roughly after a fuel pump change, the culprit could be the improper installation of the fuel pump. Specifically, there could be issues with the wiring harness. Consequently, the fuel pump may not be getting power through your system.

How to fix it

Here’s how you fix it. You will need to check that all of the connections in your electrical system are secure and that they are making good contact with their counterparts on or within the engine itself.

2. Hard start or no fuel pressure after installing fuel pump

The second common problem after installing a new pump is the hard start. Sometimes, the vehicle continues to be difficult to start when it sits for even short periods (cranks for about 30 seconds before starting).


Sometimes, after installing a new pump, there is no fuel pressure but the pump works. If there is no fuel pressure, it will prevent the engine from starting or will cause the engine to quit running.

How to Fix It

To do this, remove the line that goes into your fuel filter from the top of the tank. Then install a fuel pressure gauge on it. Plug a hose in the line going to the filter. Open up some of the vents on your hood for ventilation purposes.

The fuel pressure should be between 60-80 PSI or in other models can be anywhere from 45 psi to 55 psi. To be accurate, refer to your vehicle owner’s manual for the proper fuel-pressure range, before performing this test.

If there is no fuel in the line, then you may have a vacuum leak somewhere.

If there is too much resistance at the pump, it will continue to crank for longer periods until it gets enough fuel pressure to start. However, if there were no issues with the wiring harness along the way, your fuel pressure should be at a constant level.

If you don’t have a fuel pressure gauge, you can still diagnose fuel pressure issues using an OBD II scanner. You can read our guide on two options how to check fuel pressure without a gauge.

The next thing you need to check is the relay that controls the fuel pump and whether or not it is getting any power from your vehicle’s electrical system.

We have a detailed guide on how to test fuel pump relay using a multimeter.

3. Fuel pump is not working

If the fuel pump is installed upside down some problems that may arise are not getting enough power to start or run your engine and leaks from the bottom of your tank. Some may describe the issue as “Fuel pump not working after being replaced” or “There’s no fuel. The pump is not pumping”


The most common reason why this happens is that there is a wiring harness in the way. This is because the connector for the fuel pump was installed in an orientation opposite of where it should be and can have your fuel pump going into the engine or vice versa.

How to Fix It

You may notice that this scenario is more frequent towards aftermarket parts and not OEM parts. You will need to check all of your wiring harnesses and make sure that there are no wires in the way of your fuel pump connector.

4. Inconsistent reading on fuel gauge after replacing fuel pump

After installing a new fuel pump, you notice that your gas gauge is reading inconsistently. It will bounce back and forth between “empty” or “full”. (The pressure in a new fuel pump drops as the tank nears empty).


There are two ways to change your fuel pump. You can either replace the pump and motors only or replace the housing (which also includes the fuel gauge sending unit) completely.

If you encounter a problem with your gas gauge after installing a new fuel pump. The fuel gauge sending unit must be the culprit.

How to Fix It

If you just replaced the fuel pump and motor, then consider replacing the sending units with a new one. Or if you have installed fuel pump housing completely, then you may need a better quality sending unit.

Fuel sending units are susceptible to high temperatures and pressure from fuel. This can cause them to break down more frequently than they should, which causes this inconsistency in gas readings that you experience.

5. Fuel gauge does not work after installing fuel pump

After installing a new fuel pump, your gas gauge may not work.


Similar to inconsistent reading, this also commonly occurs if you are using an aftermarket sender that is not of good quality.

How to Fix It

This can be fixed by replacing your aftermarket fuel gauge sending unit with one that was made to fit a better vehicle. It is best to use the manufacturer’s brand rather than an “aftermarket” part because they fit best and are of better build quality.

Why is it Tricky to Change the Fuel Pump

Changing the fuel pump can be challenging. This is because the fuel pump unit sits right in front of the engine (next to and below the mass airflow sensor). 

So if you have an aftermarket intake, you may be concerned about whether it will fit or not.

What exactly do I need?

Since most problems encounter after changing the fuel pump are all related to installation procedures and materials, let’s discuss how it should be done correctly.

Likewise here’s a video from Squarebody Stuff

To change a fuel pump, here are some things that you might need:

1. A fuel pump unit of the same brand as your engine (i.e., a Honda fuel pump for a Honda, etc.) and model year. If you are unsure, consult with a professional.

2. A fuel pump relay harness and/or connectors for your vehicle.

3. Fuel pump/injector connector removal tool

4. Fuel injection wiring diagrams for your engine; this is available at the dealership.

5. Some wiring modification knowledge (or a friendly professional)

6. O2 sensor socket set

Where can I buy a new one?

You can find an OEM replacement part on any online auto parts store. You can order online and have it shipped to your home. 

How much does a fuel pump cost depends on the car where you buy it? The average cost for a fuel pump replacement is between $220 and $1,000 depending on vehicle and age. 

Labor costs are estimated between $120 and $260, while parts are priced between $95 and $850.

How to Diagnose and Replace a Fuel Pump


Tips for Preventing Common Problems after Changing the Fuel Pump

1. Before you change the fuel pump, make sure your vehicle is in a safe area to work on it.

2. Check all connections before installing the new fuel pump. Ensure they are making good contact with their counterparts.

3. Use better quality parts when replacing a fuel pump. Poor quality parts may cause problems with your gauge reading after powering up.

4. Use better quality fuel gauge sending units to prevent your vehicle from running roughly or hard starting once the tank goes empty and when it sits for even short periods.

5. Always use a cool engine to test out your newly installed fuel pump. Make sure you have no loose electrical connections.

7. Always test out the vehicle after installing the fuel pump in a controlled environment like your driveway or your garage and never on the road with traffic around.

Key Takeaways

In conclusion, the most common problems after changing the pump (engine running/idling rough, hard start, and inconsistent fuel gauge reading) resulted from improper installation and incompatible parts, it is important to learn how to install them properly or to seek assistance from a professional mechanic.

If an issue does occur due to your bad part, make sure you keep the receipt so that you can have it replaced or fixed under warranty. Always make backups of my receipts just in case something goes wrong with components that could cause further damage such as fuel pumps and oxygen sensors.

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