C9 Generator Set Engines Caterpillar

Low Fuel Pressure

Low fuel pressure can cause low power. Low fuel pressure can also cause cavitation of the fuel which can damage the fuel injectors. The following conditions can cause low fuel pressure:

• Plugged fuel filters

• Debris in the check valves for the fuel priming pump

• Debris in the pressure regulating valve

• Partially open check valve

• Sticking or worn fuel pressure regulating valve in the fuel transfer pump

• Severe wear on return fuel pressure regulating valve in the fuel filter base

• Worn gears in the fuel transfer pump

• Pinched fuel lines or undersized fuel lines

• Old fuel lines that have a reduced interior diameter that was caused by swelling

• Fuel lines with deteriorating interior surfaces

• Pinched fuel line fittings or undersized fuel line fittings

• Debris in the fuel tank, fuel lines, or fuel system components that create restrictions

High Fuel Pressure

Excessive fuel pressure can cause fuel filter gaskets to rupture. The following conditions can cause high fuel pressure:

• Plugged orifices in the fuel pressure regulating valve

• Stuck fuel pressure regulating valve in the fuel transfer pump

• Pinched fuel return line

Fuel Pressure Readings

The typical fuel pressure of the engine at operating temperature can vary. At low idle, the fuel pressure can be 538 kPa (78 psi). At high rpm, the fuel pressure can be 641 kPa (93 psi).

The performance of the unit injector deteriorates when the fuel pressure drops below 241 kPa (35 psi). Low power complaints and erratic operation can occur in this situation. Check for a plugged fuel filter or air in the fuel lines as possible causes for these complaints before replacing fuel system components.

Checking Fuel Pressure

Illustration 1	g00294866
1U-5470 Engine Pressure Group

Illustration 2	g01156167
Location of fuel pressure taps

To check the fuel pressure after the secondary filter, remove dial gauge (1) from the fuel filter base. Install the appropriate fittings and the test gauge from the 1U-5470 Engine Pressure Group and start the engine.

To check the fuel pressure between the fuel transfer pump and the secondary filter, remove plug (2) from the fuel filter base. Install the appropriate fittings and the test gauge from the 1U-5470 Engine Pressure Group and start the engine.

The 1U-5470 Engine Pressure Group includes Special Instruction, SEHS8907, "Using the 1U-5470 Engine Pressure Group". This instruction provides information about the usage of the group.