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The website said

Removes AIR / Vapor from Your Fuel
Consistent Flow of Fuel
Reliable High Volume Pumps
Increase Horse Power
Increase Torque
Increase Fuel Economy
Reduces Carbon Monoxide & Carbon Dioxide
6 Year Warranty* on Most Applications
13,000 - 15,000 Hour Life Expectancy
That Equates to 500,000 Plus Miles
Up to 200 GPH
160 Maximum PSI
Motor Has Up to 406 OZ Inches of Stall Torque
Interchangeable Filters

How can it increase economy besides eliminating the vapor.

Is there instructions somewhere for these?

There are 2 benefits.

First, when you park your truck all night the fuel settles and all the air works out. As you start and drive the truck thru the day you aggitate the fuel in the tank it becomes more and more full of small air bubbles. Think about a fish tank that you see the little air bubbles in the water when you look. With a fuel system that works like the FASS or the AirDog you will have the same pure and perfect fuel at 5PM as you had at 5AM when you started the truck. Consistant pressure fuel supply, consistant fuel quality in terms of air entrapment, and consistant power and fuel economy with less chance of any damage to injectors from air/water in the fuel cause micro bursts in the nozzles.

The other issue that varies in importance based on the truck is pressure being fed to the injection pump. Some trucks are very delicate when it comes to low or lost lift pump pressure.

Side notes would be high capacity filters that do not need as frequent maintenance and yet filter as well or better than stock. The FF-1003 filter for the FASS 150 series systems are 3 micron filters. With the FASS or AirDog you would get rock solid fuel pressure and dependable service life with both having lifetime warranties now. Both would give you a much improved system over stock.