Scout wrote:
Why would the return line cause it to lose fuel when you open the throttle?
If the purpose of the return line is to return unused fuel to the tank,
theoretically there is less fuel passing through it as you open the throttle
up.

Not necessarily. With a Detroit, yes, but other types of injector
systems do it differently. With our diesel (Ford Lehman) for example
there is almost no return at idle, the return flow seems to be
proportional to throttle setting (although it jumps when the load changes).

A blocked return line could cause the engine to die but it would be more
likely to surge or be unresponsive to throttle first (disclaimer- I am
not an expert diesel mechanic and never played one on TV)

Your advice about checking the filter again even though its new is right
on. Say Bart do you have a vacuum gage on the filter outlet?

Fresh Breezes- Doug King