Certain driveability problems can be related to the fuel quality. The Fuel Related Driveability Diagnosis table lists some of those conditions and which fuel characteristic may be the cause. However, the fuel testing is limited. Therefore, you must perform all of the system checks on the following systems before diagnosing the fuel quality:

If these checks fail to solve the problem, gain information from the customer about when the condition occurs, when and where the fuel was purchased, and which octane level was used. Ask the customer to change the fuel brands. If the symptom persists, perform the Alcohol In Fuel test below. If this symptom is not conclusive, drain the tank. Then, refill the tank with a known good quality fuel.

Certain driveability complaints such as a hesitation, a lack of power, a stall, a no start, etc. may be caused by an excessive amount of alcohol in the fuel. These complaints may be due to the following conditions:

Various types and concentrations of alcohols are used in the commercial fuel. Some alcohols are more detrimental to the fuel system components than others. If an excessive amount of alcohol in the fuel is suspected as the cause of a driveability condition, the following procedure may be used in order to detect the presence of alcohol in the fuel. In this procedure, water is used in order to extract the alcohol from the fuel. However, the specific type of alcohol (methanol, ethanol or methyl tertiary-butyl ether - MTBE) will not be determined by this procedure.

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. 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), this procedure should not be used, and the fuel system should be cleaned. Refer to Fuel System Cleaning .

1. Fill with fuel to the 90 ml mark into a 100 ml cylinder with 1 ml graduation marks.
2. Add 10 ml of water to bring the total fluid volume to 100 ml.
3. Install a stopper.
4. Shake the cylinder vigorously for 10-15 seconds.
5. Carefully loosen the stopper in order to release the pressure.
6. Close the stopper.
7. Shake the cylinder vigorously again for 10-15 seconds.
8. Carefully loosen the stopper in order to release the pressure.
9. Place the graduated cylinder on a level surface for approximately 5 minutes in order to allow for an adequate liquid separation.

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