When trying to drain the fuel filter in my 94 GMC, K2500, 6.5TD, I open the fuel cap, start the engine and then open the T-handle. An ounce+ of fuel comes out and the engine stalls. Also, I get no fuel flow out of the filter air bleed and opening it also stalls the engine. The lift pump is working since it clacks when starting and when the ig. key is turned off. What goes?