this thing is a puzzle. the engine has been starting harder last 3-4 months until it would hardly start. yesterday we changed the fuel filter, bleed the lines ( twice ), checked and cleaned the glow plugs, installed different glow plugs, held the glow plugs for 2-3 minutes, and it wouldn't fire. seemed to be turning over fast enough, but no go. only after 30 minutes of trying different throttle positions, and using the decompression lever, did it finally fire. once running, it runs great, always has.this morning, it would hardly turn over. didn't start even using the decompression lever. the batteries charged during the night. i use both deep cycle batteries to start. they are 15 months old. i pulled the batteries and took them to AUTOZONE and the tested " good". they had about 1 1/2 hours to recharge on automatic 10 amp charger.i have absolutely no idea what to do next. the engine should have spun faster this morning i think...your advise will be greatly appreciatedtom