This article explains how to test your Caterpillar 325C excavator fuel system pressure

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The tools required to test the fuel system pressure are 1U-5470 engine pressure test assembly, 3Y-2888 

connector and 3J-1970 O-ring seal. NOTE: Both the 5P-2720 Detector Engagement Unit and the 

5P-2718 Pressure Detector can be used with these tools. These additional tools will be used later when 

installing the pressure probe. Fuel leaks or splashes on hot surfaces or electrical components can cause 

a fire. Spills should be removed immediately. Keep all parts clean and free of contamination.

  Contaminants can accelerate component wear and shorten their service life. Always be careful not to 

lose fluid when inspecting, maintaining, testing, adjusting, and repairing this equipment. Suitable 

containers should be prepared to collect the liquid before opening any box or disassembling any parts 

containing liquid. All liquids should be handled in compliance with local regulations. The 1U-5470 

engine pressure test assembly is shown in Figure 3-1-46. The 1U-5470 engine pressure test assembly 

can be used to check the engine’s fuel pressure. There is a gauge in the tool set that records the 

pressure 

in the fuel manifold.

The fuel return pipe is shown in Figure 3-1-47, and the fuel pressure test is shown in Figure 3-1-48.

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Whether under normal operating conditions or under loaded operating conditions, the fuel pressure 

should be within the range of 400~525kPa; during low idle speed operation, the fuel pressure at the 

fuel 

filter inlet should be within the range of 400~435kPa. If the pressure difference AP on both sides of the 

filter is ignored, the fuel pressure in fuel supply channel 1 should be equal. For a new fuel filter, the 

pressure differential loss on both sides of it is usually 35kPa. If worn particles accumulate in the fuel 

filter, the pressure difference across it will increase. If the filter becomes clogged, the fuel supply 

pressure may drop to 69kPa before the driver notices significant power loss. If the fuel pressure is 

lower 

than normal, it will cause cavitation and cause internal damage to the unit injector. The pressure 

difference on both sides of the fuel filter should not exceed 69kPa. The pressure regulator 3 is installed 

directly on the cylinder head. The pressure regulator is located at the fuel return port, which is toward 

the rear end of the fuel supply channel 1. The oil hole maintains the fuel pressure at low engine speeds.

  When checking the fuel pressure on the unfiltered side, follow these steps:

(1) Remove the plug from the fuel pressure gauge port 6. (2) Install the joints, seals and 1U-5470 

engine pressure test assembly to the fuel pressure gauge interface 6, so that the pressure of the fuel 

transfer pump can be measured. When checking the fuel pressure in fuel supply passage 1, follow the 

steps below.

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 1) Remove the plug from the fuel pressure gauge port 7. 

 2) Install the connector, seal and 1U-5470 engine pressure test assembly to fuel pressure gauge port 7.

  3) Run the engine. NOTE: Before checking fuel pressure, make sure the fuel filter is clean. A clogged 

fuel filter will cause the pressure at fuel pressure gauge port 7 to be lower than the pressure at fuel