FASS 2001-2010 Duramax 6.6L Titanium Signature Series - 165GPHFASS 2001 2010 Duramax 6. 6L Titanium Signature Series 165GPH A FASS Fuel Systems can be a beneficial upgrade for your GM Duramax 6. 6L diesel engine, this is because your Duramax doesnt come with a factory System like other diesels. This requires your CP3 injection System to pull your fuel under a vacuum, adding additional stress to your CP3 System and risk introduce additional air into your fuel. This is where a Titanium FASS Fuel System comes in to