How to Troubleshoot the Fuel System in Vehicles

by Contributing Writer; Updated June 12, 2017

In a carbureted Harley, gasoline flows from the gas station, to the gas tank, by gravity through the petcock to the carburetor, then to the intake valves after which it explodes. In a fuel-injected Harley the gas is pumped from the fuel tank to the fuel injectors, which spray the gasoline into the intake valves. The most likely components to malfunction in a fuel-injected bike are the fuel pump or any of the multiple electronic sensors on such a bike. The fuel system on a fuel-injected Harley is diagnosed electronically. Troubleshooting the fuel system on a carbureted Harley is less susceptible to electronic gremlins and may be more illustrative of what makes these Vehicles go.

Under The Hood:

 How to Troubleshoot the Fuel System in a Nissan Sentra

Check the weather channel or your local weather readings, first, to see if there is a possibility that you have Vapor Lock or ice in your fuel tank. When the temperature is below 30 degrees, adding de-icing in the gas tank may help. In heat above 80 degrees, pour cool water on the fuel pump and the fuel lines.

Park your car on a level surface, add some gas to the tank, and try starting the vehicle again. When your car is at an angle, the fuel injector may be pulling in air instead of gas.

Test the spark plugs with a spark plug tester. These testers can be purchased at most car part stores. Once you connect a spark plug to the tester and turn the car on, you should see a spark in the gap. If no spark appears, you should replace every spark plug.

Take off the fuel line with a fuel line disconnect tool, place it in a clear container, and start the engine. You should see fuel coming out of the line when the engine is engaged. If you do not see any fuel, you need to have the fuel pump tested and possibly replaced. If you are unable to reach the fuel line, as it is located under the passenger's side of the vehicle on a Nissa Sentra, you may have to take it to a mechanic who can lift the vehicle into the air.

Examine your rubber fuel hoses. Remove them, squeeze them for soft or brittle spots, and replace the hoses if any of them have these problems.

Items you will need

  • Spark plug tester

  • Fuel line disconnect tool

 How to Troubleshoot the Fuel System on a Harley-Davidson

Open the gas cap and smell the gasoline. Shine a flashlight into the tank. If you see water or diesel oil floating on top of the gasoline, you must drain the fuel from the carbureted Harley.

Disconnect the hose clamp that secures the fuel line to the petcock with a flat-head screwdriver. Replace the fuel line at the petcock with a 2-foot length of 1/4-inch rubber hose.

Insert the open end of the hose in an empty, 5-gallon gas can. Open the petcock to "reserve" and drain the fuel.

Unscrew the petcock from the bottom of the fuel tank with an open-end wrench. Examine and, if necessary, clean the fuel filter.

Reinstall the petcock with an open-end wrench. Replace the fuel line on the petcock using a screwdriver and put 1 gallon of fresh gasoline in the fuel tank.

Open the petcock, open the choke, put the bike in neutral and attempt to start the motorcycle.

Open the throttle if the bike starts and fully close the choke. Run the motorcycle until the rocker box covers are warm to the touch and allow the throttle to return to normal idle. If the engine dies at a normal idling speed take the following steps.

Restart the motorcycle and idle the bike with the choke pulled halfway out. If the bike runs with the choke half out, but not pushed fully in, the fuel-air mixture in the carburetor has too much air and not enough gasoline.

Items you will need

  • Flashlight

  • Flat-head screwdriver

  • 2 feet of 1/4-inch rubber hose

  • 5-gallon gas can

  • Open-end wrenches

  • 1 gallon fresh gasoline

 How to Troubleshoot the Fuel System in a Saturn Ion

Refuel the Right Way

Identify your Saturn Ion's engine type--a 2.2L L4, 2.4L L4 or a 2.0L Supercharged--by looking at the eighth character of your car's VIN (vehicle identification number). If it's an "F," you have a 2.2L L4 engine; a "B" indicates a 2.4L L4 type; and a "P" identifies the 2.0L Supercharged.

Buy the correct octane level based on your Saturn Ion's classification. Cars with the 2.2L L4 engine can get by with regular unleaded gas with at least an 87 level. Ions with either the 2.4L L4 or 2.0L Supercharged need to use premium unleaded fuel with an octane of 91 or higher.

Keep an appropriate amount of gas in your tank at all times for optimal efficiency and operation. Fill-up immediately whenever the "LOW FUEL" light displays. This means you only have 1.5 gallons of gas left.

Use caution when you refuel. Don't smoke, run the engine, spill the gas or leave the pump unattended when filling up. Secure the Saturn Ion's cap tightly when you're done to prevent the "CHECK GAS CAP" or "CHECK ENGINE" lights from appearing.

Respond to Warning Signals

Stop the car whenever the "CHECK ENGINE" light comes on, which points to potential fuel, ignition and emission problems. If the light is steady, the gas cap may be the wrong type, loose or missing. Try tightening the cap and then restart the car. If the light doesn't disappear, it's a more serious problem.

Pay attention to any knocking sounds you hear. A light noise or "spark knock" means you're not using the right fuel type. It'll stop as soon as you switch to the correct one. If it's a heavier sound and you're already using at least an 87 octane fuel, your engine needs service.

Inspect the Saturn Ion's fuel for dirt or moisture whenever the engine sounds irregular or rough. Other possible causes are a clogged air filter or a problem with the fuel pump.

Troubleshoot the carburetor's choke or plate, if the engine is hot and won't start. You could also just be out of gas.

Perform Regular Fuel System Safety Checks

Check and change your oil regularly to prevent damage to your fuel system and engine. The owner's manual recommends checking it each time you refuel. If the oil dipstick is at or below the minimum mark, you need to add more. Whenever your "CHG OIL" light appears on the instrument panel, change the oil.

Monitor your Saturn Ion's fuel efficiency. If you get consistent low gas mileage, clean the carburetor and replace the air filter, if your car's fuel system includes these components. If the problem continues, check to see if the choke is defective.

Follow the Saturn Ion's fuel system maintenance schedule. Every 25,000 miles, inspect your fuel system for damage or leaks. Also change your engine fuel filter at the 100,000 mile marker.

Perform any repairs discovered in your periodic fuel system inspection. In addition to the fuel filter, these actions can also include replacing the fuel injector and pump in models with these components.

Items you will need

  • Owners manual