Fuel Pump: Testing and Inspection

Mechanical Fuel Pump Operation:

NOTE: Prior to performing fuel pump tests inspect all hoses and lines, for kinks and bends that may cause restrictions. Inspect the weep hole in the fuel pump housing for fuel leakage. If fuel is leaking out of the weep hole or the pump is determined to be defective, replace the pump as an assembly.

VACUUM TEST
1. Disconnect the low-pressure fuel inlet fitting at the mechanical fuel pump.
2. Install a T-fitting between the disconnected inlet fitting and the mechanical fuel pump inlet.
3. Connect a vacuum gauge to the T-fitting.
NOTE: The vacuum gauge will not indicate a vacuum until the mechanical fuel pump reaches full operating capacity.

4. START the engine and hold the engine speed at 1500 rpm for 30 seconds. Vacuum should not exceed 3.75 in. Hg (12.7 kPa)
5. If vacuum exceeds 3.75 in. Hg (12.7 kPa), check the fuel inlet tube for a restriction. A partially clogged in-tank fuel filter can also cause excessive vacuum.
6. Bleed the air from the fuel system.

VOLUME TEST
1. Disconnect the low pressure fuel inlet fitting at the injection pump.
2. Position the low pressure hose so fuel can be discharged into a graduated container.
3. CRANK the engine for 30 seconds and check how much fuel has discharged into the graduated container. The mechanical pump should have delivered .70 quart (.75 liter) of gasoline into the graduated container.
4. Bleed the air from the fuel system.