I'd done a search and found a bunch of FASS topics but nothing that seems similar to what I'm having, If I'd missed it sorry but I'm going to ask.

I have a 2005 F350 6.0 that I just put a FASS system on (maybe) a month ago with it I'd installed an electric pressure transducer from amazon and it didn't work worth crap (through my Edge Insight) I'd gotten a new sensor and got it installed the other day and it seems to be working the way it should, Now I have info to go with my issue.

I'd got the Fass system to, mainly, remedy the low fuel issue from the stock pickup in my titan tank (with the added benefit of the advertised "saves the injectors, cleans the fuel, etc") but I'd noticed that on occasion the truck sputters, with this working pressure transducer I see that I am having "normal" pressures in the 60's (usually 64-68/69psi) which I know is "in range" but today, for instance, I had to brake quick and with that my fuel pressure (at the FASS pump) went down to ~10psi, I think it was, and kept falling to around 1psi kind of like it'd sucked in air then after a bit (a block or three) it re-primed itself and the pressures went back to the 60's, also when parked facing down hill it'd do it too. is there some kind of fix for this issue or is this a "New issue"?

I'd noticed after I'd installed the pump that the truck didn't seem to have the same "umph" that it did with the stock pump connected to it. Does anyone have experience with these things to chime in oh how good or bad they actually are? So far I'm REALLY not impressed....
I'm also curious how hot the pump/motor is supposed to run, I haven't put a thermometer to it yet but I've had my hand on it and it's HOT but not hot enough to make you have to remove your hand to keep from getting burned or anything.

I don't know if there's a FASS rep person here or not like I've seen on a Dodge forum I'd found from Google but hopefully if so they can chime in too.

I'd hate to have wasted the $600.00+ (Black Friday deal) on the pump (and extras I'd got) to just have to go back to the stock pump/pickup, If I do I'll have to get a new pickup (another $300.-400.00) anyway, the black pickup funnel thing seems to be missing from mine.

One way or another I'd like to have this figured out and fixed before I put my bed back on since working on it would be SO MUCH EASIER with it off.

 

You could be experiencing the pick up tube lose issue or dropped off. Does it only happen at less than half a tank or even when filled right up? You may need to drop the tank to confirm but this is a known issue. There is a Matt you can buy that sits on the bottom of the tank that always pulls even if not submerged. But this may be more costly than just fixing the pickup tube or atleast checking it.

 

Have not had good luck with FASS on several trucks. I now run a 6.7 pump on my 6.0 and a Beans Diesel sump. All my fuel problems are gone and if I do have a pump go out I can get one from any Ford Dealer or most aftermarket parts stores.

 

Last time I had the tank down (2 weeks ago maybe) to check the tube length it seemed nice and tight. I'm thinking, like i think you suggested, fuel slosh in the XXL titan tank, rush to the front starving the straw letting it suck air but I still have 1/2 if not more of a tank since the factory pickup/float is less than 1/2 way down the tank.
What really gets me is I don't recall it doing it with the stock pump even though the pickup is missing the black plastic funnel thing from the bottom of it (discovered that when I dropped the tank last time).

I have to get my fuel bowl pressure sensor on so I can measure the stock pump.... if/when I un-bypass it.

 

that little plastic thing on the bottom is the fuel pick-up and I believe it a one way valve.Enough searching should show that when that thing is missing, guys with 1/4 tank full of fuel with stock tanks have issues.

 

Well, I got the fuel filter pressure sensor on and when the FASS would loose prime/pressure (down to the 1's or lower) the engine pressure was 0. Just as a side not there was a slight pressure drop/difference between the FASS pump and the motor sensor, I don't recall the numbers but I think it was like 2 PSI or something, Just for information's sake. So I undid the FASS which is now just along for the ride. I wish I knew how to get it to work right so I don't end up wasting all that money I could have used elsewhere, How have the people that have these successfully set up have them? anyone with one working right reading this?
The only thing I can think of is to get 2-3 sumps and link them together but then I got the exposed lines under the (titan)tank which, IMO, already sits low enough which is why I didn't want to do sumps in the first place. CC-LB with LITTLE off-road use but have been out.
Well, I un-bypassed the FASS and I'm back on the stock pump (Minus the pick-up pre-screen thing) and the pressures from the stock pump are 66-69psi at idle and drop to somewhere below 50 at ROMP (I don't know the number but my insight is hollerin' at me since I have the alert set to 50). so Now I have to find some time to drain the tank of 1/2 (around 30gal) of fuel to put that pickup thing on. and while i'm there i can triple (quadruple, sep-tuple... whatever number it'll be) the FASS tube which I'm sure is fine and I'm convinced it's slosh but should still be submerged in fuel since I have (at least) 1/2 a tank still.