- Disconnect the inlet line (coming from the filter) at the pump. Connect
a vacuum gauge to the pump nipple. Remove the coil-to-distributor high tension
cable at the coil.
- Have an assistant crank the engine with the key as you watch the gauge.
A vacuum should be produced in a regular cycle as the pump turns over. There
should be no blowback of pressure (abrupt drop in vacuum or even positive
pressure for a short time). If there is blowback of pressure, the inlet valve
on the pump is leaking and the unit must be replaced.
- The vacuum shown with each pump stroke should be strong and constant. If
the vacuum is low (or none at all), the diaphragm is leaking and the pump
must be replaced.
- Inspect the small breather hole or tube (above the diaphragm) which vents
the pump's upper chamber. Leakage of fuel or oil here confirms that the diaphragm
or oil seal is leaking.
- Inspect the end of the pushrod and the contact surface on the pump operating
lever. Replace the pushrod or pump if there is obvious wear. If the camshaft
end of the pushrod is badly worn, remove the valve cover and inspect the camshaft
eccentric (which operates the fuel pump) for excessive wear.
- If the pump has a lever arm, check the contact pad (face) of the lever for
wear or scoring. Inspect the camshaft if heavy scoring is present. Check the
motion of the arm and the tension of the spring.
