C9.3B 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

• Contamination in the check valves for the fuel priming pump

• Sticking or worn fuel metering 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

• Contamination 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 metering valve in the fuel transfer pump

• Pinched fuel return line

Checking Fuel Pressure

Illustration 1	g00293196
1U-5470 Engine Pressure Group

Refer to Special Instruction, SEHS8907, "Using The 1U-5470 Engine Pressure Group" for more information. Refer to Operating Manual, NEHS0818, "Using the 198-4240 Pressure Indicator Tool Group" for more information.

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Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. Clean up fuel spills immediately.

1. Use the following procedure in order to measure the fuel pressure that is 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, achieving an average reading and a steady needle. Keep the gauge above the measuring point.

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   Illustration 2	g03117257
   C9.3B fuel filter base (1) Input fuel (2) Output fuel (3) Fuel pressure sensor/ Test port

   1. Install the 1U-5470 Engine Pressure Group into port (3). This port is the proper test port.

   2. Adjust the engine speed to 1800 rpm with no load.

   3. The fuel pressure should be 586 kPa (85 psi) nominal. Record the pressure.

   4. If excessive pressure is found, check the conditions that are listed previously under the "High Fuel Pressure" heading.
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   Illustration 3	g06258438
   C9.3B fuel transfer pump mounted on the high-pressure fuel pump

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   Illustration 4	g06258445
   C9.3B fuel transfer pump (4) Low-pressure fuel inlet (5) Low-pressure fuel outlet (6) Pressure regulating valve

2. Use the following procedure to check the output of the fuel transfer pump:

   1. Remove the fuel line (4).

   2. Tee the 1U-5470 Engine Pressure Group into the port that contained the fitting for the fuel line (5) .

   3. Adjust the engine speed to 600 rpm with no load.

   4. The fuel pressure should be 690 kPa (100 psi) to 724 kPa (105 psi).

   5. If the fuel pressure is within the specified range, proceed to Step 3.

   6. If the pressure is less than 655 kPa (95 psi), the fuel transfer pump is weak. The fuel metering valve (6) in the pump may be stuck or worn. Remove the fuel metering valve, the spring, and the pin. Inspect the fuel metering valve. If contamination is not found, and the fuel metering valve is worn out, replace the fuel transfer pump. If dirt is found, clean the valve assembly and reinstall the valve assembly.

   7. Check the fuel pressure again. Replace the fuel transfer pump if the fuel pressure still measures less than 655 kPa (95 psi). The fuel transfer pump is operating properly if the fuel pressure measures at least 690 kPa (100 psi) to 724 kPa (105 psi).

   8. Once the fuel transfer pump has been confirmed as properly operating, check the fuel pressure again after the secondary fuel filter base. Refer to Step 1. If the fuel pressure is not at the nominal specification, continue to Step 3.
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   Illustration 5	g06258450
   C9.3 fuel manifold (7) Fuel pressure regulating manifold (8) Return line from the cylinder head (Input) (9) Return to tank (output) (10) Fuel rail pressure relief valve leak off

3. Use the following procedure to inspect the return pressure regulating manifold:

   1. Return fuel pressure regulating manifold (7) is located above the ECM.

   2. The return fuel pressure check valve may be stuck or worn. If contamination is not found, and the fuel pressure regulating manifold wears out, replace the fuel pressure regulating manifold.

   3. Check the fuel pressure again after the secondary fuel filter base. Refer to Step 1. If the fuel pressure is not up to 586 kPa (85 psi), then perform Step 4. If the primary filter is sized correctly and the fuel lines are sized correctly, replace the secondary fuel filter base.

4. Use the following procedure to measure the vacuum at the primary filter:

   1. Adjust the engine speed to 1800 rpm with no load.

   2. Measure the vacuum at the outlet of the primary filter.

   3. The vacuum should be 10.14 kPa (3 in Hg) to 13.52 kPa (4 in Hg). If the vacuum is more than 30.42 kPa (9 in Hg), measure the vacuum at the inlet of the primary filter. The differential across the primary filter should be less than 3.38 kPa (1 in Hg) with a new filter installed. If the differential is higher by more than 3.38 kPa (1 in Hg), the filter is undersized. The filter should be rated at 341 L (90 US gal) per hour. If the filter is sized correctly, ensure that the fittings and lines are correctly sized. The fuel lines should be 12.7 mm (0.5 inch). Also check for debris in the fuel tank that may be plugging the supply tube.