Fuel Pump: Testing and Inspection

Fuel Transfer Pump Pressure Test

For operation of the fuel transfer pump primer button, refer to Fuel Pump/Description and Operation.

Fuel Heater And Temperature Sensor Location:

The fuel transfer pump is located on the left side of the engine and above the starter motor.

An improperly operating fuel transfer pump can cause low engine power and/or hard engine starting. Inspect the fuel supply line to the pump for restrictions, kinks or leaks.

Fuel leaking from the weep hole in the pump casing indicates a leaking pump. The transfer pump must then be replaced or rebuilt.

Do not operate the fuel system with a fuel line or component suction restriction of more than 100 MM Hg (4.0 inch Hg).

Low transfer pump output can be caused by a worn eccentric on the engine camshaft.

The maximum allowable fuel pressure drop across the fuel filter/water separator is 35 kPa (5 psi). As the filter removes contaminants in the fuel, the pressure drop across the fuel filter/water separator will increase. Frequent replacement of the filter may indicate a worn transfer pump. The filter/separator can be checked with a fuel pressure gauge. For test procedures, refer to Fuel/Water Separator/Testing and Inspection/Procedures.

Output Pressure Test

Fuel Line Fittings:

1. Remove the clamp bolt retaining the fuel drain manifold line to the cylinder head.
2. Remove the rear banjo fitting bolt at the inlet line.
3. Position the fuel drain manifold line to the rear.

Special Tool Installation:

4. Install and tighten special adapter tool 6829 into the top of the fuel inlet line.
5. Install a 0-60 or 0-100 psi fuel pressure gauge to adapter tool 6829.
6. Start engine and record fuel pressure. Minimum pressure should be 172 kPa (25 psi).
7. If fuel pressure falls below specifications, test for fuel line inlet restrictions before condemning the fuel transfer pump. Proceed to step a:

Rubber Fuel Hose, Pump To Heater:

a. Remove the rubber fuel hose and clamps located between the fuel heater and fuel transfer pump.

Installing Hose Adapter:

b. Install special hose adapter tool 6837 between the disconnected fittings on the heater and transfer pump. Install clamps to hose tool 6837.

Installing Vacuum Gauge:

c. Connect vacuum gauge 6828 to T-fitting as shown.
d. Start the engine and observe the vacuum gauge. The vacuum gauge will not indicate a vacuum until the transfer pump begins to operate at full capacity. Inlet restriction must not exceed 100 mm Hg (4 in. Hg). If the restriction is higher than the specifications, check for a kinked fuel line or a plugged fuel tank vent. A partially clogged in-tank fuel filter can also cause excess vacuum. Repair as necessary.

8. Remove vacuum gauge and adapter hose tool.
9. Install rubber fuel hose and clamps between heater and pump.

Fuel Volume Test

Fuel volume-versus-engine cranking RPM are used for the test.

Electronic Components:

WARNING: TO PREVENT THE ENGINE FROM STARTING, DISCONNECT THE PIGTAIL HARNESS AT THE FUEL SHUTDOWN SOLENOID. USE CAUTION AS RESIDUAL FUEL IN THE FUEL INJECTION PUMP MAY CAUSE THE ENGINE TO START AND RUN TEMPORARILY. CONTINUE TO RUN THE ENGINE UNTIL IT QUITS BEFORE PERFORMING THE FUEL VOLUME TEST.


1. Connect a hand held tachometer to the engine. Use Cummins part number 3377462 or an equivalent.

Fuel Line Fittings:

2. Remove the clamp bolt retaining the fuel drain manifold line to the cylinder head.
3. Remove the rear banjo fitting bolt at the inlet line.
4. Position the fuel drain manifold line to the rear.

Fuel Volume Test:

5. Install and tighten special adapter tool 6836 into the top of the fuel inlet line.
6. Connect a temporary rubber fuel hose to adapter 6836.
7. Place the other end of this temporary hose into a graduated container.
8. Crank the engine for 30 seconds. Measure the fuel volume in the container after 30 seconds of engine cranking time. Do not crank the engine for more than 30 seconds at a time. Starter motor damage may result.

Fuel Volume Specifications:

9. To determine the correct fuel volume, refer to Fuel Volume Specification. To use the chart, refer to the following procedure:

^ Draw a straight vertical line at the measured RPM.
^ Draw a straight horizontal line at the measured fuel volume.
^ If these two lines intersect below the flow line, this indicates a defective transfer pump or a line restriction.
^ If these two lines intersect above the flow line, this indicates acceptable fuel flow.