The white, step-shoulder filter tucked under the plumbing on the rear passenger side of the Duramax is probably the most important filter under the hood – and hardest to get to.
The water separation/fuel filter is a pain to change, but vital to saving you thousands in injector repairs because it’s the only item keeping water from reaching the injectors.
“The fuel filter should be replaced every other oil change (or if there’s a water-in-fuel warning on the dash display),” says Rod Halsten, a master GM diesel technician.
“When the Water-In-Fuel (WIF) sensor, located at the bottom of the fuel filter, sends a signal to the computer warning there’s water in the fuel, turn the engine off immediately. Don’t drive it another 50 miles thinking the warning isn’t that serious. It is.”
Servcie tip: Handle the plastic WIF sensor with extreme care – both unscrewing it from the OEM filter and replacing it on the new filter.
Over-tightening and rough handling of the GM WIF sensor will lead to major issues. Handle it with care when replacing the filter.
“Owners and fleet mechanics have a tendency to over-tighten the sensor, which leads to it cracking. When that happens, air gets in the system and the truck will start and die or crank and not start at all. Finger-tight and a 1/4-turn more is all you need.”
Another tip: Stretch the larger of the two o-rings that comes with the GM filter a couple times before placing it on the filter and it will seat in the filter’s retaining groove perfectly every time.
Service tip: Don’t use cheap aftermarket water/fuel filters because they don’t have the extra water-trapping space afforded by the GM factory filter’s step-shoulder design.
“That little bit of extra space can mean the difference between saving the injectors or not. So being cheap here can cost you thousands of dollars down the road.”
Over-tightening and rough handling of the GM WIF sensor will lead to major issues. Handle it with care when replacing the filter.
