The mech. lift pump could be weak? I know that when changing filters it takes alot of additional cranking to fill the new filter and lines back with diesel. My battery was charged, but ran weak after all the cranking. I have heard of people installing electric lift pumps is to aid the system, it seems like a good idea. I wanted to hear from anyone who did it, what their opinion is. I'm well aware of the 606 issues with air in the lines. After changing all lines and O-rings I still found air at the first clear line from the thermostat (heater) to the pre filter (strainer). I now changed the rubber hose which connects the thermostat to the metal fuel line entering the engine bay. I thought that the rubber hose might be the source of air entering the system before the fuel even gets to the motor. I plan on getting an additional fuel filter/strainer on that line which I can see into. Note: I eliminated the intank strainer when I pulled my tank out to clean.