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Engine surfaces and fluids can be hot. A running engine will have moving belts exposed at the front of the engine (rear of bus). These hazards can result in personal injury or death. stop the engine while connecting test equipment and work carefully around a running engine. Do not allow tools or test equipment to protrude or vibrate into the path of rotating belts. |
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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 (if equipped)
- Sticking or worn fuel pressure regulating valve in the fuel transfer pump
- Severe wear on return fuel pressure regulating valve at the rear of the cylinder head
- 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
Checking Fuel Pressure
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| Illustration 1 | g00293196 |
1U-5470 Engine Pressure Group | |
Refer to Special Instruction, SEHS8907, "Using The 1U-5470 Engine Pressure Group".
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Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. Clean up fuel spills immediately. |
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| NOTICE |
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Keep all parts clean from contaminants. Contaminants may cause rapid wear and shortened component life. |
| NOTICE |
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Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
Use the following procedure to measure the fuel pressure after the secondary filter:
Note: Fuel pressure readings near the fuel supply manifold have pressure spikes. The pressure spikes are caused by excess fuel that is returning to the fuel system from the injectors. Excessive needle movement at the gauge may be present. Connect the gauge with a section of suitable hose. The air in the hose absorbs the spikes. This gives an average reading and a steady needle. Keep the gauge above the measuring point.
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| Illustration 2 | g00945275 |
(1) Plug | |
Install the 1U-5470 Engine Pressure Group into port (1) .
During both normal operating conditions and load conditions, the fuel pressure should register the following range:
- 455 to 579 kPa (66 to 84 psi)
At low idle, the fuel pressure at the fuel filter's inlet should be at the following amount:
- 400 to 434 kPa (58 to 63 psi)
The fuel pressure to the fuel gallery should be the same amount, if you subtract the change in pressure (delta P) across the filter.
With a new filter, the pressure drop across the fuel filter typically registers the following amount:
- 35 kPa (5 psi)
As deposits collect on a fuel filter, the pressure differential will increase. Engine misfire may occur if the fuel pressure in the fuel gallery decreases to approximately 69 kPa (10 psi).
The fuel pressure regulator valve is mounted at the fuel return port at the rear of the fuel gallery in the cylinder head. The fuel pressure regulating valve maintains fuel pressure at low engine rpm. The regulating valve also contains a spring loaded check valve. The spring loaded check valve prevents the fuel from draining from the fuel gallery back to the fuel tank after engine shutdown.
Unit Injector Hydraulic Pump (Test)
Injection Actuation Pressure (Test)
The test for injection actuation pressure is used in order to check for the following conditions:
- The unit injector hydraulic pump is producing maximum pressure.
- The pump pressure regulator is working properly.
- The unit injector hydraulic pump is worn.
- System leaks
The Caterpillar Electronic Technician (Cat ET) is used to perform this test.
Dead Head Test for the Unit Injector Hydraulic Pump
The unit injector hydraulic pump dead head test is used to verify that the following conditions exist:
- The injection actuation pressure circuit is working.
- The unit injector hydraulic pump is working properly.
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| Illustration 3 | g00749695 |
High pressure line | |
| Required Tools | ||
|---|---|---|
| Part Number | Part Name | Quantity |
| 125-2580 | Tool Group For HEUI | 1 |
To check the pressure for the unit injector hydraulic pump, remove the pump outlet line (1) from the pump. Install the appropriate gauge from the 125-2580 Tool Group For HEUI . The gauge to use should have a range that would include 34 MPa (5000 psi).
Note: Be sure to install a cap or plug the fitting that goes into the high pressure oil gallery.
Crank the engine for approximately 3 seconds in order to get the maximum pressure.
If the recorded pressure is less than 26.5 MPa (3850 psi), the pump should be replaced.
If the recorded pressure is equal to or greater than 26.5 MPa (3850 psi) the pump is operating properly.