Driveability Problems Table

Fuel System Diagnosis (Driveability Problem Table):

Engine Controls (Fuel Injectors):

Fuel System Diagnosis (Fuel Quality)

Certain driveability problems can be related to fuel quality. The Fuel Related Driveability Problems table lists some of those conditions and which fuel characteristic may be the cause. However, fuel testing is limited. Therefore, all other system checks 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 Fuel System Diagnosis test. 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 tertiary-butyl ether- MTBE) 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 go 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. Close the stopper and shake vigorously again for 10-15 seconds.

7. Carefully loosen the stopper to release pressure.

8. 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.

Always begin fuel and air control system diagnosis with, Fuel System Check. This table will identify other tables for specific checks, such as:

^ Fuel Pressure Check

^ Injector Flow/Voltage Drop Check

^ Power Balance Check

^ Idle Speed Control Check