I removed a leaking rear fuel tank on my '93 F-250 7.3L. I'll be running off the front tank alone, but engine is now running rough and smoking. I've plugged the supply and return lines going to/from the rear tank and have tried running out any air in the system. No luck. Is there a step or trick I've missed? I haven't has issues using the front tank before, so a bit perplexed.

 

Check the vent for the front tank. Make sure it is open.

 

I pulled the vent hose cap (per suggestion), but changed nothing. I've bypassed the tank selector valve since posting earlier. Thought I may have moved some sediment and plugged it, so I'm running direct from tank to pump, and return to tank. Its as if I'm getting too much fuel now, or starving it for air.
Can't imagine unplugging the rear sending unit has anything to do with anything....?

 

What is the color of the smoke you're getting?

 

It's white. Definitely fuel.

 

Have you run through whatever fuel was in the tank and tried some fresh?