GM Service Manual Online
For 1990-2009 cars only

Alcohol-In-Fuel

Notice: Do not use fuels containing methanol in order to prevent damage and corrosion to the fuel system.

Alcohol-in-fuel can be detrimental to the fuel system components. Alcohol-in-fuel can 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, or the 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 in order to detect the presence of alcohol in the fuel.

Testing Procedure

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 to bring the total fluid volume to 100 ml.
  3. Install a stopper.
  4. Shake vigorously for 10 to 15 seconds.
  5. Carefully loosen the stopper to release the pressure.
  6. Install the stopper.
  7. Shake vigorously again for 10 to 15 seconds.
  8. 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 measure more than 10 ml. For example, if the volume of the lower layer is increased to 15 ml, it will indicate at least 5 percent alcohol in fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.