Automotive Fuel System Repairs

Diagram showing the operation of a 4-stroke spark ignition engine. Labels: 1 ‐ Induction, 2 ‐ Compression, 3 ‐ Power, 4 ‐ Exhaust. CC-BY-SA 3.0 Zephyris

Internal combustion engines burn an air-fuel mixture to create power which drives the vehicle. The internal combustion occurs within cylinders that house pistons. Air and fuel are drawn into the cylinder and they are ignited which causes the piston to move down. There may be six or eight of these cylinders and pistons, each firing in a specific order so that when one piston goes down, the adjacent piston goes up. As they go up and down they systematically rotate a crankshaft.

Then the rotational energy of the crankshaft is eventually transferred to the wheels through a series of gears and shafts. After the combustion, the gas byproduct exits the engine through the Exhaust System.

The purpose of the fuel system is to store and deliver the fuel required for the internal combustion process. It works closely with the electrical system so that the timing is just right for fuel to be injected into the cylinder, mixed with air and then ignited with a spark in regular gasoline vehicles. In a diesel engine the fuel is ignited with compression.

The major parts of the modern fuel system include the fuel tank, fuel lines, fuel pump, fuel filter, fuel regulator and fuel injectors. Modern vehicles are also equipped with a computer that records diagnostic codes from sensors throughout the vehicle, including sensors in the fuel system, and it plays a very specific role for regulating how much fuel is injected into the engine while the engine is running.

When you fill your vehicle with fuel from a gas station, the fuel will have contaminants that are harmful to the engine if they are not filtered out. Between the fuel tank and the engine, the fuel passes through a sock filter which prevents large contaminants from passing through, also called a fuel tank strainer. Then the fuel will pass through the fuel filter which prevents small contaminants from passing. Anything that passes through the fuel filter can pass through the rest of the fuel system. Another crucial filter that prevents contaminants from entering the engine is the air filter.

The fuel pump is responsible for pumping the fuel from the fuel tank (usually near the rear wheels) to the engine (usually over the front wheels). The fuel injectors inject the fuel directly into the engine cylinders, which is much more efficient than outdated carburetors. The vehicle’s Emissions System also helps improve fuel efficiency. A pressure regulator controls fuel pressure to ensure good engine performance under a variety of speed and load conditions. Some vehicles use a return line system to return unused fuel back to the tank.

Prior to 1985 most vehicles (almost all of them) used a carburetor. A carburetor is a primitive method of mixing air and fuel. It is far less efficient than modern fuel injection, and when they were around they required frequent tuning and rebuilding. If you’re old enough to remember when carburetors were common then you might be familiar with the song “Shut Down“, released in 1963 by the Beach Boys:

It happened on the strip where the road is wide
Two cool shorts standin’ side by side
Yeah, my fuel injected Stingray and a four-thirteen
Revvin’ up our engines and it sounds real mean

Tach it up, tach it up, tach it up
Buddy gonna shut you down

At the time these lyrics were written fuel injection was a novelty, used mostly only in racing, high performance vehicles similar to what supercharging and turbocharging are today (which are also becoming more common). Now everyone has fuel injection unless your still driving one of those old classics. Crawford’s Auto Repair has experienced mechanics that can fix older vehicles if you have them, and carburetor repair is no problem for us (unless the parts simply can’t be found).

Fuel System Maintenance

The fuel system is inspected with the regular maintenance checks that Crawford’s performs during every oil change and at landmark mileage checks (30K, 90K and 100K miles). During this inspection the technician will take the vehicle for a test drive. If there are any symptoms or dashboard warning lights that could be related to the fuel system then the technician will note those and investigate further after the test drive. In the shop the technician visually inspects any part of the fuel system that can be done without disassembly, both under the hood and with the vehicle raised on hydraulic lifts.

The owner’s manual is consulted for the fuel filter maintenance schedule. It should be changed often, but how often depends on the vehicle manufacturer’s recommendation. In older vehicles the filter should be changed at least every 2 years. Some performance fuel filters will have a washable mesh, which eliminates the need for replacement.

The fuel filter is changed with every tune up. Traditionally the tune up is simply considered to be a spark plug replacement service, but it’s actually a “combustion cycle optimization” service. The timing of fuel injection is part of that optimization so the fuel system is checked and adjustments made if needed.

When discussing maintenance for other vehicle parts and systems there is often a portion of that discussion dedicated to maintaining the fluid for that system. That’s not the case for the fuel system since there is such a high turnover. Indeed, here in the area of Chandler, AZ most drivers have to refill their vehicles with fuel every 1-2 weeks. If any fuel leaks are discovered on inspection then they will need to be repaired.

DIY Fuel Maintenance Tips For the Vehicle Owner

Occasionally when filling up at the gas station, take a moment to check your tire inflation, oil level, windshield wiper fluid and battery. Most people don’t do this but technically it’s supposed to be done each time you fill up with gas, which is why we used to have full service gas stations. Or at least check your oil once a month.

Where you buy your gas can make a difference. Some of the smaller gas stations might take what’s left from a delivery truck after it’s made all it’s other stops. This means you’re getting the gas from the bottom of the barrel. This could have more contaminants or even higher water content and water is known to cause rust in the engine.

This is unconfirmed but we’ve also heard that if the truck is in the process of making the delivery (i.e. it’s filling the station’s tanks underground) then the flow of gasoline could be stirring up contaminates that have previously settled at the bottom of the tank. Both the sock filter and fuel filter have been discussed, but there’s no sense in wearing them out quicker if it can be avoided. If there is any truth to this, then you’d want to avoid filling your vehicle while the gas station is getting resupplied.

There is no need to use higher octane fuel unless your vehicle’s manufacturer recommends it. If the manufacturer doesn’t recommend it, then it’s a waste of money. Choose the lower octane available at the station.

A regular addition of fuel system cleaner like STP Injector Cleaner, or Techtron fuel system cleaner can help keep your injectors clean. This prevents particle build up in the injectors. If the build up occurs then the buildup can prevent the injectors from opening and the engine won’t start or the injectors can be forced to stay open and inject too much fuel during the combustion process. Using a fuel system cleaner can be done as often as every three months.

You can monitor your gas mileage with mobile apps for Apple or Android and compare it with this widget tool below. If you find that you’re getting worse gas mileage than you should be getting then bring your vehicle to the shop for an inspection.