I have a 1990 superduty with a 7.3 that after I replaced the fuel pump and filter the truck after a week has become very hard to start if it's warm or cold. You have to spray diesel fuel in the air cleaner to start after it sits.
i have found no fuel leaks, return lines are clean without leaks, no injectors leaking. And no check engine light.
Any ideas to try?

 

I know a few trucks have been installed with a clear fuel line leading up to the filter. This is a good way to see if you have air intrusion from either the fuel line from the tanks/pump or the return lines.

 

So far I haven't found a extra fuel filter in the lines anywhere.

 

If the fuel system wasn't loosing it's prime before you replaced the lift pump and filter,then those are subject.Inspect the filter is screwed on tightly with a clean rubber ring and the lift pump lines have good hose clamps.You may have forgotten to tighten one or it's still not snug enough.

If you meant to say "because" the truck was hard to start,that was the reason for replacing the lift pump and fuel filter.Then that changes things of course and the entire fuel system is still suspect.

 

You'll never get a check engine light for a running problem; it's a completely mechanically-controlled engine.

Air intrusion is indeed your prime suspect. As said, if it was NOT hard to start before the work, the areas of work would be the place to focus.

How old are the return lines and return cap o-rings? The clear line trick mentioned above will help you find air intrusion. Start by replacing the return line going to the filter head with a piece of 1/4" clear tubing. Start and run it for a while; opening up the system will introduce air so it'll be even harder to start. But that air should eventually self-purge; if you continue to see bubbles in the clear line after running a while, you've got air intrusion in the return system. Do any of the return lines or return caps appear dark/stained? Any other sign of leaking fuel?

Does it behave the same way on both tanks? How much fuel is in the tank you're using?

 

Typical idi prime loss. As said above, need to know when the hard start began.

Rotary pumps have a light-medium service life. If, after diligent research, you deem the system to be leak free then you probably just need a new injection pump.