For those who have a vacuum gauge to monitor VO & #2 fuel filter restriction, how much difference of a vacuum reading do you see at idle and at 55 mph? You know the filter is clogged when the high vacuum reading is at idle or at 55 mph? How many inches of vacuum indicate to you to change the filter?
I realize the Super Duty fuel systems run on pressure, but the OBS is a vacuum system. I just installed a vac gauge in the cab to monitor fuel restriction. On VO there is 2" of vacuum at idle and 2" at 55 mph. On #2 I see about 2" at idle and about 7-8" at 55 mph with brand new filters so I think there may be a restriction in the #2 fuel supply line. The VO lines are 3/8" ID hose throughout. The diesel supply has 3/8" hose too but also the smaller steel line that runs under the truck. Normally there should be more vacuum on VO but that's not the case.
I used compressed air and blew the diesel steel line clean but after a test drive the vacuum reading at 55 mph was still 7-8".
So if I were to get 3/8" hose throughout the diesel side will the vac reading at 55 mph be like the VO reading of 2" at 55 mph since all filters are new, the VO is hot, and both have the same 3/8" ID supply lines?
So if it's normal for the vacuum to rise as you go faster why is my VO reading so much lower than my #2 reading?