Alcohol/Contaminants-in-Fuel Diagnosis Without Special Tool

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

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 in order to bring the total fluid volume to 100 mL. Install a stopper on the cylinder.
3. Shake the cylinder vigorously for 10 to 15 seconds.
4. Carefully loosen the stopper to release the pressure.
5. Close the stopper and shake the cylinder vigorously again for 10 to 15 seconds.
6. 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 be more than 10 mL. For example, if the volume of the lower layer increases to 15 mL, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.

Alcohol/Contaminants-in-Fuel Diagnosis With Special Tool

J 44175 Fuel Composition Tester

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector, at the lowest point in the fuel rail, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust, or deterioration.

Alcohol concentrations of greater than 10 percent can be detrimental to fuel system components. Excessive alcohol may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Fuel with excessive alcohol may cause driveability conditions such as hesitation, lack of power, stalling, or no start. Some types of alcohol are more detrimental to fuel system components than others. This vehicle was not designed for fuel that contains methanol. If you suspect excessive alcohol in the fuel is the cause of a driveability condition, use the following procedure to test the fuel quality.

1. Turn ON the J 44175 fuel composition tester.

If the green LED does not illuminate, refer to the fuel composition tester user manual.

2. Verify the fuel composition tester is operational by measuring the AC frequency output with a DMM. Refer to Measuring Frequency in Wiring Systems.

A frequency of between 35 Hz and 48 Hz without a fuel sample in the test cell indicates that the tester is working correctly.

3. Install the fuel pressure gauge. Refer to Fuel Pressure Gage Installation and Removal .




Important: The fuel pressure gauge will need to be bled a few times in order to obtain an accurate fuel sample from the vehicle being tested.

4. Close the bleed valve on the fuel pressure gauge.
5. Place the bleed hose (1) of the fuel pressure gauge into the 100 ml beaker (2).
6. Use a scan tool in order to command the fuel pump ON.
7. Slowly open the bleed valve on the fuel pressure gauge, until an adequate fuel sample is obtained.
8. If water or sediment appears in the fuel sample, clean the fuel system and replace the fuel in the vehicle. Refer to Fuel System Cleaning .




Important: Do not allow any substances other than gasoline, ethanol/gasoline blends, air, or acetone into the test ports of the fuel composition tester. Contaminants in the fuel composition tester could result in misdiagnosis.

9. Pour the fuel sample from the beaker (1) into the J 44175 , until the level of the fuel is at the top of each fuel test port (2).
10. Observe the diagnostic LEDs on the fuel composition tester.

If the red fuel diagnostic LED is illuminated, a fuel contamination condition exists. Refer to Fuel System Cleaning .

11. Measure the output frequency of the fuel composition tester.
12. Subtract 50 from the reading on the DMM to obtain the percentage of alcohol in the fuel sample. Refer to the examples in the following table.
13. If the fuel sample contains more than 15 percent ethanol, add gasoline to the fuel tank or replace the fuel in the vehicle.