Fuel System Inspection
A problem with the components that send fuel to the engine can cause low fuel pressure. This can decrease engine performance. To inspect the fuel system, follow this procedure:
- Check the fuel level in the fuel tank. Inspect the fuel tank cap. Make sure that the vent is not filled with dirt.
- Check the fuel lines for fuel leakage. Make sure that none of the fuel lines have a restriction or a damaged bend.
- Install a new fuel filter. Clean the primary fuel filter.
- Remove any air that may be in the fuel system.
If there is air in the fuel system, use the priming pump to open the drain valve on the fuel injection pump housing. Drain the fuel system until fuel without air flows from the drain line.
Follow these steps when you drain air from the fuel injection lines:
- Loosen the fuel line nuts on the fuel injection valve by 1/2 turn.
- Move the governor lever to the LOW IDLE position.
- Crank the engine with the starting motor until fuel without air flows from the fuel line connections.
- Tighten the fuel line nuts.
Note: The fuel priming pump will not provide enough pressure for pushing fuel through the reverse flow check valves in the fuel injection pumps.
Checking Engine Cylinders Separately
If any of the following conditions occur, check the individual engine cylinders:
- The engine runs rough.
- The engine misfires.
- The exhaust system blows out black smoke.
Use this procedure to check the engine cylinders separately:
- Run the engine at the roughest speed.
- Loosen the fuel line nut at a fuel injection pump. This will stop the flow of fuel to that engine cylinder.
After you shut off an engine cylinder's fuel flow, the engine should run rough.
| NOTICE |
|---|
The fuel injection nozzles can be permanently damaged by twisting if only one wrench is used to loosen or tighten the fuel line nuts. Use one wrench to hold the nozzle and another to loosen the nut. |
- Tighten the fuel line nut.
- Repeat Step 1 through Step 3 with each engine cylinder in sequence until you discover a loosened fuel line that does NOT affect the engine's performance.
- When you find the engine cylinder that does NOT affect the engine's performance, perform the following operations:
- Test the fuel injection pump for that cylinder.
- Test the fuel injection nozzle.
When an engine runs at low idle rpm, the temperature of an exhaust manifold can indicate the condition of a fuel injection nozzle. A low temperature indicates that no fuel is reaching the cylinder. This can possibly signify that the fuel injection nozzle has a defect.
When an engine runs at low idle rpm and the temperature of an exhaust manifold is at an extra high temperature, too much fuel is probably flowing into the engine cylinder. This can also signify that the fuel injection nozzle has a defect.
The most common defects on fuel injection nozzles include the following defects:
- Plugging or blocking by carbon on the tip of an fuel injection nozzle
- Orifice wear due to abrasive particles in the fuel
- Wear from a wire brush on the nozzle's tip
Refer to Special Instruction, SEHS8149 for the procedure for checking the temperatures in the exhaust manifold port.