Test Procedure
NOTE:
Numbers in parenthesis in the following steps correspond to components in referenced figures.
- Turn Fuel Composition Tester (J 44175) on.
- Verify the fuel composition tester is operational by measuring the AC frequency output using a DVOM. A frequency without a fuel sample in the test cell indicates that the tester is working correctly.
- Install Fuel Pressure Gauge (J 34730-A), or equivalent.
- Close the bleed valve on the fuel pressure gauge.
- Place the bleed hose (1) of the fuel pressure gauge into the 100 ml beaker (2). See Fig 1.
- Using a scan tool, command the fuel pump ON.
- Slowly open the bleed valve on the fuel pressure gauge, until an adequate fuel sample is obtained.
- If water appears in the fuel sample, replace the fuel in the vehicle. See FUEL SYSTEM CLEANING .
- Pour the fuel sample from the beaker (1) into the Fuel Composition Tester until the level of the fuel is at the top of each fuel test port (2). See Fig 2.
- Observe the diagnostic LEDs on the fuel composition tester. If the Red fuel diagnostic LED is illuminated, a fuel contamination condition exists. See FUEL SYSTEM CLEANING .
- Measure the output frequency of the fuel composition tester.
- Subtract 50 from the reading on the DVOM to obtain the percentage of alcohol in the fuel sample. See examples in FUEL COMPOSITION TEST EXAMPLES table.
- If the fuel sample contains more than 10 percent ethanol, replace the fuel in the vehicle.
NOTE:
Bleed the fuel pressure gauge a few times to obtain an accurate fuel sample.
FUEL COMPOSITION TEST EXAMPLES
| Example | Frequency - Hz | Subtract 50 | Ethanol Percent |
| A | 50 | -50 | 0 |
| B | 65 | -50 | 15 |
| C | 129 | -50 | 79 |