Alcohol-in-fuel can be detrimental to fuel system components and may cause driveability problems such as hesitation, lack of power, stall, no start, etc. The problems may be due to fuel system corrosion and subsequent fuel filter plugging, deterioration of rubber components, and/or air-fuel mixture leaning. Commercial fuel uses various types and concentrations of alcohol. Some types of alcohol are more detrimental to fuel system components than others. If you suspect an excessive amount of alcohol in the fuel as the cause of a driveability condition, use the Alcohol-in-Fuel Testing Procedure to detect the presence of alcohol in the fuel.

Draw the fuel sample from the bottom of the tank in order to detect any water present in the tank. The sample should be bright and clear. If the sample appears cloudy or contaminated with water as indicated by a water layer at the bottom of the sample, do not use this procedure. Refer to Fuel System Cleaning.

1. Fill a 100-mL cylinder with fuel to the 90-mL mark.
2. Add 10 mL of water in order to bring the total fluid volume to 100 mL. Install a stopper on the cylinder.
3. Shake the cylinder vigorously for 10 to 15 seconds.
4. Carefully loosen the stopper to release the pressure.
5. Close the stopper and shake the cylinder vigorously again for 10 to 15 seconds.
6. Put the graduated cylinder on a level surface for approximately 5 minutes in order to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer, which would now contain both alcohol and water, will be more than 10 mL. For example, if the volume of the lower layer increases to 15 mL, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.