I was plowing snow and snowing blowing when the tractor just stopped. About 28F, just right for the snowblower to work. Engine stopped . Would crank but no firing. figured fuel issue, icing or at least water in the fuel. Have been adding diesel supp;lement all fall so I believe the fuel is OK. Changed both filters, used the transfer pump and cranking to be sure there was fuel thru the filter bleed screws. Opened each injector line and bled them one at a time. Still no fire. Bled lines again and still some air bubbles. Is there a way for the system to get an air lock? The only thing I did not bleed was the bleed valve on top of the pump. In a bad spot with the loader frame and it was stuck. Didn't want to break it off. Cranking plenty fast as I just hooked jumpers to the battery and kept it warm while I was working on it. Been in the mid 30's for a couple days but still no go. Only thing I haven't tried is pulling. It is headed up hill and even chained up I just spin out. does the injector pump make any unusual noise if it stops working??