OK, this has been a mind boggler for me. My truck is a 6.9 idi and it has 2, yes i said 2, as in T-W-O, inline fuel filters and the big glass filter like what you find on some older tractors has been by passed for some reason . i am the third owner so i have no idea when it was like this. would i benefit from hooking up the glass filter or leave it as is?

 

The glass one, is it mounted on the firewall? If so, that's the water separator, and most everyone bypasses it because it can cause air leaks and the your truck will not start. I would leave it bypassed. The later trucks didn't have it.

 

Ok thanks I didn't know it was the water separator like I said it looked like those glass fuel filters

 

My 7.3 has two inline filters. A Racor R60P 30 micron filter and water separator prepump and then a Cat 1R0749 2 micron post pump filter. Then again, I ditched the factory fuel system.

The better the fuel is filtered, the longer the pump and injectors should last.