Alcohol/Contaminants-In-Fuel Testing Procedure

Table 6C-1:

DESCRIPTION
Certain driveability problems can be related to fuel quality. Table 6C-1 lists some of those conditions and which fuel characteristic may be the cause. However, fuel testing is limited. Therefore, all other system cheeks must be performed (e.g. Powertrain System, Fuel System, Ignition System, Emission System) before fuel quality is diagnosed. 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 fuel brands. If the symptom persists, perform the "Alcohol In Fuel" test below. If this is not conclusive, drain the tank and refill with a known good quality fuel.

Certain driveability complaints such as hesitation, lack of power, stall, no start, etc. may be caused by an excessive amount of alcohol in fuel. These complaints may be due to fuel system corrosion and subsequent fuel filter plugging, deterioration of rubber components and/or air/fuel mixture leaning.

Various types and concentrations of alcohols are used in commercial fuel. Some alcohols are more detrimental to 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 to detect the presence of alcohol in the fuel. In this procedure, water is used to extract the alcohol from the fuel. However, the specific type of alcohol (methanol, ethanol or Methyl Tertiarybutyl Ether - MTE) will not be determined by this procedure.

TESTING 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.

1. Using a 100 ml cylinder with 1 ml graduation marks, fill with fuel to the 90 ml mark.

2. Add 10 ml of water to bring the total fluid volume to 100 ml and install a stopper.

3. Shake vigorously for 10-15 seconds.

4. Carefully loosen the stopper to release pressure.

5. Close the stopper and shake vigorously again for 10-15 seconds.

6. Carefully loosen the stopper to release pressure.

7. Place the graduated cylinder on a level surface for approximately 5 minutes 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 greater 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 greater because this procedure does not extract all of the alcohol from the fuel.

FUEL SYSTEM DEPOSITS
Fuel system deposits can cause various driveability problems. Deposits usually occur during hot soaks after key "OFF." Poor fuel quality or driving patterns such as short trips followed by long "cool down" periods can cause injector deposits. This occurs when the fuel remaining in the injector tip evaporates and leaves deposits. Leaking injectors can increase injector deposits. Deposits on fuel injectors affect their spray pattern, which in turn could cause reduced power, unstable idle, hard starts and poor fuel economy.

Intake valve deposits can also be related to fuel quality. While most fuels contain deposit inhibitors, some do not and the effectiveness of deposit inhibitors varies by manufacturer. If intake valve deposits occur, fuel may be suspected. These deposits can cause symptoms such as excessive exhaust emissions, power loss and poor fuel economy.