My 601 will start then it dies after about 15 seconds and the yellow warning exclaimation point is lit on control panel along with an icon indicating "low HST pump pressure". I changed the fuel filter and cleaned the water separator filter then bled the air from system using the lever on the fuel supply pump. Also changed engine ooil and filter. Also changed chain drive case oil both sides. Air filter not changed but looks ok. Initially after fuel filter change it would not start at all but now at least starts though it does not run well. Any ideas? Would low hydraulic oil pressure cause a shutoff. Thanks