Low Fuel Pressure
Low fuel pressure can cause the engine to have low power. Low fuel pressure can also cause cavitation in the fuel system. Cavitation of the fuel 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
| Required Tools | ||
| Part Number | Part Description | Quantity |
| 1U-5470 | Engine Pressure Group | 1 |
| 3Y-2888 | Connector | 1 |
| 3J-1907 | O-Ring Seal | 1 |
 | |
| Illustration 1 | g00294866 |
1U-5470 Engine Pressure Group | |
 | |
| Illustration 2 | g01064133 |
Location of the fuel pressure tap | |
To check the fuel transfer pump pressure, remove the plug from the fuel filter base. Install the 3Y-2888 Connector with a 3J-1907 O-Ring Seal. Install a pressure gauge, and start the engine.
The 1U-5470 Engine Pressure Group can be used in order to check the fuel pressure of the engine. The engine pressure group includes Special Instruction, SEHS8907, "Using the 1U-5470 Engine Pressure Group ". This instruction provides information about the usage of the group.