Air in Fuel
This procedure checks for air in the fuel. This procedure also assists in finding the source of the air.
- Examine the fuel system for leaks. Ensure that the fuel line fittings are properly tightened. Check the fuel level in the fuel tank. Air can enter the fuel system on the suction side between the fuel transfer pump and the fuel tank.
- Install a 2P-8278 Fuel Flow Tube (Sight Gauge) in the fuel return line. When possible, install the sight gauge in a straight section of the fuel line that is at least 304.8 mm (12 inches) long. Do not install the sight gauge near the following devices that create turbulence:
- Elbows
- Pressure relief valves
- Check valves
Observe the fuel flow during engine cranking. Look for air bubbles in the fuel. If the engine starts, check for air in the fuel at varying engine speeds. When possible, operate the engine under a load and look for air in the fuel.
- Elbows
- If excessive air is seen in the sight tube in the fuel return line, install a second sight tube at the inlet to the fuel transfer pump. If a second sight tube is not available, move the sight tube from the fuel return line and install the sight tube at the inlet to the fuel transfer pump. Observe the fuel flow during engine cranking. Look for air bubbles in the fuel. If the engine starts, check for air in the fuel at varying engine speeds. When possible, operate the engine under a load and look for air in the fuel.
If excessive air is not seen at the inlet to the fuel transfer pump, the air is entering the system after the fuel transfer pump.
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| Illustration 1 | g00578151 |
2P-8278 Fuel Flow Tube (Sight Gauge) (1) A steady stream of small bubbles with a diameter of approximately 0.1588 cm (0.0625 inch) is an acceptable amount of air in the fuel. (2) Bubbles with a diameter of approximately 0.635 cm (0.25 inch) are also acceptable if there is two seconds to three seconds intervals between bubbles. (3) Excessive air bubbles in the fuel are not acceptable. | |
- Pressurize the fuel tank to 35 kPa (5 psi). Do not use more than 55 kPa (8 psi) in order to avoid damage to the fuel tank. Check for leaks in the fuel lines between the fuel tank and the fuel transfer pump. Repair any leaks that are found. Check the fuel pressure in order to ensure that the fuel transfer pump is operating properly. For information about checking the fuel pressure, see Testing and Adjusting, "Fuel System Pressure - Test".
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To avoid personal injury, always wear eye and face protection when using pressurized air. |
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| NOTICE |
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To avoid damage, do not use more than 55 kPa (8 psi) to pressurize the fuel tank. |
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