Donaldson, Parker/Racor, AcDelco all claim 4 micron although the Donaldson claims 99% efficiency at 4 microns, have to question that one based on the date of the PDF bottom right May 2009. I do not recall ever reading about a 2 micron OEM or replacement filter even in some of the old archived sites...
http://www.catching.com/wp-content/..._A_PFF50216_GM_Duramax_Diesel_Fuel-Filter.pdf
http://www.catching.com/wp-content/..._A_PFF50216_GM_Duramax_Diesel_Fuel-Filter.pdf
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