C27 and C32 Engines Fuel System Pressure - Test Caterpillar


Fuel System Pressure - Test
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1.1. Low Fuel Pressure
2.1. High Fuel Pressure
3.1. Fuel Pressure Readings
4.2. Lower Fuel Pressure Configuration
5.2. Higher Fuel Pressure Configuration
6.1. Checking Fuel Pressure

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 fuel 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

Different configurations are used for the low-pressure side of the fuel system. The different configurations cause different fuel pressure readings.

Lower Fuel Pressure Configuration

The typical fuel pressure of the engine at operating temperature can vary. With new fuel filters, the fuel pressure at the secondary fuel filter base must be within the following ranges. At cranking speed (100-135 rpm), the fuel pressure can be 75 kPa (11 psi). At low idle (700 to 900 rpm), the fuel pressure can be 450 ± 50 kPa (65 ± 7 psi). At high idle (1800 to 2000 rpm), the fuel pressure can be 500 ± 50 kPa (73 ± 7 psi).

The performance of the unit injector deteriorates when the fuel pressure drops below 390 kPa (57 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.

Higher Fuel Pressure Configuration

The typical fuel pressure of the engine at operating temperature can vary. With new fuel filters, the fuel pressure at the secondary fuel filter base must be within the following ranges. At cranking speed (100-135 rpm), the fuel pressure can be 75 kPa (11 psi). At low idle (700 to 900 rpm), the fuel pressure can be 650 ± 50 kPa (94 ± 7 psi). At high idle (1800 to 2000 rpm), the fuel pressure can be 705 ± 50 kPa (102 ± 7 psi).

The performance of the unit injector deteriorates when the fuel pressure drops below 390 kPa (57 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.

There are two available pressure regulator valves and there are two sets of pressures:

  1. Equipped with 327-0376 Check Valve Gp. At cranking speed (100–135 rpm), The fuel pressure can be 500 kPa (72 psi). At low idle (700 to 900 rpm), the fuel pressure can be 500 to 700 kPa (72 to 101 psi). At high idle (1800 to 2000 rpm), the fuel pressure can be 600 to 900 kPa (87 to 131 psi).

  2. Equipped with 228-7381 Check Valve Gp. At cranking speed (100–135 rpm), The fuel pressure can be 350 kPa (51 psi). At low idle (700 to 900 rpm), the fuel pressure can be 450 to 650 kPa (65 to 94 psi). At high idle (1800 to 2000 rpm), the fuel pressure can be 600 to 800 kPa (87 to 116 psi).

Checking Fuel Pressure

Table 1
Required Tools 
Part Number  Part Name  Quantity 
1U-5470
or
198-4240 
Engine Pressure Group
or
Digital Pressure Indicator 


Illustration 1g00294866
1U-5470 Engine Pressure Group


Illustration 2g01124671
Location of fuel pressure tap
(1) Plug


Illustration 3g02124374
(2) Pressure tap

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

Check the fuel pressure of the engine with the 1U-5470 Engine Pressure Group. 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.

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