How to Drain the Fuel Water Separator on a Duramax
• Remove the fuel cap - this releases pressure from the fuel system and will allow the fuel water separator to drain completely.
• Locate the fuel filter housing. It is on the passenger side of the truck, inside the engine compartment. The water drain valve is located on the bottom of the fuel filter.
• Position a container beneath the water drain valve to collect the fuel/water.
• Open the drain valve a couple of turns (2-3) and allow all the fuel/water to drain. Once all the fuel/water has drained from the housing, completely close the valve, hand tight only.
• Reinstall the fuel cap and run the engine. If the engine runs rough or stalls, air may be trapped in the fuel system. If the engine continuously stalls, you may need to prime the fuel system.
How to Purge Air from the Fuel Lines on a Duramax
• To prime the fuel system, first gently loosen the bleed screw a few turns (do not remove it). Now press down on the primer (located on the top of the fuel filter housing) continuously until fuel comes out the bleed screw, then close the bleed screw.
• Cycle the key into the on position several times for up to a 60 second intervals. This will allow the fuel pump to cycle and purge the system.
• Start the engine and allow to run for several minutes or until it idles smoothly.