Water contamination in the fuel system can cause driveability conditions such as hesitation, stalling, no start, and sporadic misfires. Water contamination in the fuel system can also cause a misfire at a single cylinder from water pooling near a single injector, usually at the lowest point in the fuel rail in some fuel systems. Once enough water collects in this area, the injector may receive a shot of water, causing an intermittent misfire in that cylinder.

Alcohol concentrations of more than 10 percent in fuel can be detrimental to the fuel system components and may cause driveability problems such as hesitation, lack of power, stalls, or no start. The problems may be due to fuel system corrosion and subsequent fuel filter plugging, deterioration of rubber components, and air-fuel mixture leaning.

Various types and concentrations of alcohol are used in commercial fuel. Some alcohol is 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 following procedure in order to detect the presence of alcohol in the fuel.

Draw the fuel sample from the bottom in order to detect any water that is in the tank. The sample should be bright and clear. If the sample appears cloudy, or if the sample appears to be contaminated with water, indicated by a water layer at the bottom of the sample do not use this procedure. Clean the fuel system.

1. Using a 100-mL specified cylinder with 1-mL graduation marks, fill the 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, and install a stopper.
3. Vigorously shake the cylinder for 10 to 15 seconds.
4. Carefully loosen the stopper in order to release the pressure.
5. Re-install the stopper, and shake the cylinder vigorously again for 10 to 15 seconds.
6. Place the 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 will now contain both alcohol and water, will be more than 10 mL. For example, if the volume of the lower layer is increased to 15 mL, there is at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat greater because this procedure does not extract all of the alcohol from the fuel.

Draw the fuel sample from the bottom of the tank so that you can detect any water that is in the tank. The sample should be bright and clear. If the sample appears cloudy or if the sample appears to be contaminated with water, as indicated by a water layer at the bottom of the sample, use the following procedure in order to diagnose the fuel.

1. Using an approved fuel container, draw approximately 0.5 liter of fuel.
2. Place the cylinder on a level surface for approximately 5 minutes in order to allow the particulate contamination to settle.
3. Observe the fuel sample. If any physical contaminants or water are present, then clean the fuel system. Refer to Fuel System Cleaning .

Particulate contamination will appear in various shapes and colors. Sand will typically be identified by white or light brown crystals. Rubber particles are typically black and irregular. Rust may appears as brown, cloudy fuel, or as brown particles. Any particles, regardless of color or shape, are unacceptable. Thoroughly clean the entire fuel system.