GMC 2003 C4C042 Owner's Manual page 266

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5. Open the fuel filter vent
valve by turning the
screw counterclockwise
several full turns.
6. Repeatedly press down
on the fuel filter primer
pump with the palm
of your hand. Let the
pump return upward
between presses.
7. Operate the priming pump until a small amount of
fuel seeps from the vent valve. When you see the
fuel, the filter is now full of fuel and the system
should be primed.
8. Close the vent valve.
9. Clean any fuel which accumulated on the fuel filter.
10. Start the engine and let it idle for a few minutes.
11. Check the filter for leaks.