Symptoms of a Bad or Failing Fuel Line

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on December 17th, 2024

Reading Time: 4 minutes
Summary
  • A bad fuel line will show symptoms like poor gas mileage, fuel smell, and visible fuel leaks.
  • There are a number of things that can cause a fuel line leak. Fuel can soak into the hose over time and break it down, causing cracks and leaks.
  • Depending on what section of the fuel line needs replacing, new parts can cost anywhere from $10 to $530. The difference in price often depends on whether you need a rigid or a flexible section.

A leak in your vehicle’s fuel line could spell a lot of trouble, especially for a fuel injection system.

As the fuel pump sends pressurized fuel through the feed line, a leak  in the fuel line can cause problems ranging from fuel smell to poor fuel economy, even to a vehicle fire.

Your vehicle’s fuel injection line is a network of flexible and rigid lines used to transport fuel throughout the fuel system.

Bad Fuel Injection Line Symptoms

This is why it’s important to watch for the symptoms of a leaky fuel line, which may include the following:

Poor Gas Mileage

One symptom of a leak in your fuel line is poor gas mileage. If the fuel leak is this bad, you should see fuel dripping on the ground.

Car Smells of Fuel

Leaked fuel will always fill the air around the vehicle with the smell of gas.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: If you’re running your A/C on “vent” or “norm,” you may smell leaking fuel inside the car. Look for visible leaks if you smell gas. In some cases, mere fuel vapor from a bad gas cap can cause a gas smell, but that’ll typically set an EVAP code on OBD2 systems.

Visible Leaks

If your fuel line springs a leak while on the road, it can start spraying gas everywhere, leading to puddles along the street and a mess under the hood. Your vehicle will likely also come to a full halt as it loses pressure in its injection system.

Of course, any drops or puddles of gas under your vehicle should immediately be cause for concern. However, smaller leaks are more difficult to spot. You can add fuel-safe dye to your gas tank if you want to make any leaks easier to see.

Inspect the fuel lines carefully for visible symptoms to identify a leak. If you see any damp areas with a buildup of gunk along any of the tubes or hoses, you likely have a bad fuel line on your hands.

Cracks on Fuel Hoses on Older Vehicles

The soft hose parts of your fuel line (if equipped),are more prone to cracking if the material soaks in the gas. Older fuel injection systems like the 4.0L Jeeps from 1987-1990 have rubber fuel hoses feeding the fuel rail. The older the fuel hose, the more likely this will happen. Look over your hoses carefully to make sure they aren’t cracked and leaking.

What Causes a Fuel Line Leak?

Fuel injection first became prevalent in the mid 1980s, and the injectors don’t have a “line” for each injector. The injectors receive their fuel supply from a common rail that is pressurized by a pump in the fuel tank, which usually produces from 40 to 80 psi of fuel pressure, depending on the platform.

Fuel injection first became prevalent in the mid 1980s, and the injectors don’t have a “line” for each injector.

Richard McCuistian, ASE Certified Master Automobile Technician

That supply fuel line comes from the fuel pump in the tank to the injector fuel rail on both return and returnless systems. There’s also a fuel return line going back to the tank on return systems that have the fuel pressure regulator mounted on the fuel rail.

Diagram of return and returnless fuel systems | Image Source: Richard McCuistian

There are a number of things that can cause a fuel line leak. Different factors affect different parts of the line as well. The rigid parts of the line won’t be subject to all the same problems as the flexible sections, which are made of hard plastic.

For instance, permeation is a large problem for the soft, flexible hose parts of a fuel line. Permeation is what happens when fuel soaks into the hose over time and breaks it down, causing cracks and leaks. Many hoses are also more prone to breaking down due to the ethanol in modern fuel.

Meanwhile, corrosion is something the metal parts of your fuel lines will need to contend with.

Fuel lines as a whole will suffer from age and occasional abrasions. The abrasions can come from other parts of the vehicle rubbing against the lines or debris finding its way into the system. No matter how good your fuel line is, it will eventually break down and need replacing.

How Much Does It Cost To Replace a Bad Fuel Line?

Depending on what section of the fuel line needs replacing, new parts can cost anywhere from $10 to $530. The difference in price often depends on if you need a rigid or a flexible section. Either way, all fuel injection lines are made to withstand the extreme pressure that comes with an injection system.

Maintaining your fuel line is essential for traveling safely in your vehicle. Any leaks in the system can cause a myriad of problems, so stay on top of things and keep an eye out for any of the fuel leak symptoms we’ve discussed.

About The Authors
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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CarParts.com Research Team and Richard McCuistian, ASE Certified Master Automobile Technician
Tags: fuel-line