Changed the fuel filter today and noticed some strange pressure readings. I went though the normal procedure I always do and when I got it started the pressure was about 1-2 pounds lower than normal. Took it for a short drive and then it shot up to normal pressure at idle. Got home and the pressure dropped down another pound at idle. Weird. Tried stabing the throttle and then tried releasing the filter drain while it was running to possibly push out any trapped air. Got the pressure to about 1/2 lb below normal. Now I know that 1/2 lb isnt a big deal but after running this EXACT pressure reading for 6 months I dont see why simply changing the filter would cause any drop in pressure. Unless there is air possibly trapped in the housing. Well if no one has had this happen, I will just drive it for a while and see if there is any fluctuation.

 

Double check for any leaks in the filter housing or lines toward the VP.

 

No leaks.

 

is it pre filter or post??

if it is pre then yes pressure will drop a pound or 2.....this is becuase there is less restriction in the line now!!! same idea as your exhaust...take out the muffler and egts will drop because there is less restriction!!

 

KATOOM,

Silly question, still the same make/media fuel filter??

 

Yes it is the same filter. Same as I always use, too.

I never thought about the drop in pressure being do to less restriction, though. I was informed that by tapping post filter I could tell if the filter was getting dirty by the DROP in pressure, not increase. By adding a new filter the resistance should be lower and in reality that should raise my pressure just by design of the LP and the bypass system. But this theory doesnt apply to other flow measures.

Anyway, it seems to be back up to normal now. I think it was just some trapped air in the filter housing/lines causing an incorrect reading.

 

cool beans, I run an in-cab pre filter and an underhood pre and post just to keep an eye on things...