STEP 2698023 - Caterpillar

Measuring Filtered Fuel Pressure
Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. Clean up fuel spills immediately.
A high pressure fuel line must be disconnected. To avoid personal injury or fire from fuel spray, the engine must be stopped before the fuel line is disconnected.
Refer to "Fuel System Identification" in order to identify the correct location for measuring the filtered fuel pressure. Install Tooling (A) into pressure test location (2) in order to measure the filtered fuel pressure.Note: A fuel sensor may be installed in one of the ports that are indicated in the illustrations. If a fuel sensor is installed in the port, install a tee fitting into the port. Install the sensor and Tooling (A) onto this tee prior to operating the engine. Ensure that the tee and all fuel fittings are securely tightened. Failure to tighten all fittings could result in serious fuel leaks.Clean any residual fuel from the engine components.
Start the engine.
Record the pressure reading that is on Tooling (A) for engine speeds of 600 rpm and 1800 rpm. The test should be performed with no load on the engine.Note: Excessive needle movement at the gauge may be present. Fuel pressure readings near the fuel supply manifold will be affected by pressure spikes. The pressure spikes are caused by excess fuel that is returning to the fuel system from the injectors. If the gauge is connected with a suitable length of hose, the air in the hose will absorb the spikes. This will give you an average reading and a steady needle. Ensure that the gauge is elevated above the pressure measuring port during the test.
Stop the engine and remove Tooling (A) from the fuel system.Fuel Filter Differential Pressure
Calculate the fuel filter's differential pressure by subtracting the filtered fuel pressure from the unfiltered fuel pressure. For best results, use the pressures that have been measured at an engine speed of 1800 rpm.Typically, the differential pressure for a new fuel filter will not exceed the 35 kPa (5.0 psi).As abrasive particles collect in the fuel filter, the pressure differential across the filter will increase. When a filter becomes plugged, the pressure differential may increase as much as 69 kPa (10.0 psi) before a significant power loss is detected by the operator. Low filtered fuel pressure will cause cavitation of the fuel and internal damage to the unit injectors. The pressure differential across the fuel filter should not exceed 69 kPa (10.0 psi).If a high differential pressure exists, replace the fuel filter. Refer to Testing and Adjusting, "Fuel System - Prime" for information on priming the fuel system after you replace the fuel filter.Fuel Pressure Relief Valve
Illustration 6 g00996532
Fuel transfer pumpTypical example (3) Fuel pressure relief valveThe fuel pressure relief valve (3) is an internal component that is located in the fuel transfer pump. The relief valve is used to regulate the maximum pressure for the fuel system. Refer to Illustration 6 in order to locate the pressure relief valve.The maximum unfiltered fuel