FASS fuel system, is it worth it???

[aceduramax]

Just wondering if someone might have messed with the FASS fuel air seperator systems yet? Maybe kennedy??? Well ive put them on a few dodges and they seem to work pretty sweet, just wondering if they do the same for the dmaxes???

[Kennedy]

I believe that the FASS and Preporator play on the fear of air in relation to the "big truck" fuel systems of old where the transfer pump was on the engine/inj pump and "pulled" the fuel from the tank. These systems were fully mechanical, and relied on housing pressure and pop pressure to inject the fuel. Air messes with these pretty good, and can delay injection events (timing) severely. When Two Guys Garage did their quick "pitch" for the Fass they rocked the rank, but couldn't get the air to show (as air naturally separates to the surface) in their clear lines so they had to kink the supply line and causing severe cavitation/aeration to illustrate.


For the Dmax, most of you are familiar with my Mega filter and it's uncanny ability (not necessarily by design) to trap air. What we found was simply add a lift pump and the unaltered Mega will not catch any air. By design, it is about impossible for air to dip down from the underside of the head, pass thru the media, and get out the hole in the center of the deep draw post. Additionally for those not running a lift pump, we have a modification to the post that allows air to pass air like the OE system does without issue.


Now that I have that out of the way, the Dmax pulls it's fuel from a pickup in a cup type of sump. At levels over about 1/3 tank this cup fills from above. Below 1/3 it relies on return fuel to help fill the cup. The FASS is a simply a glorified pump/filter with a built in bypass regulator mounted at a high point so as to encourage the air to return to the tank. Drop psi below the bypass point and nothing returns. In operation it returns this fuel to a point generally in the filler neck. This does not allow fueling while running, lets the fuel spill into the tank making more air. This also puts a high demand on the fuel in the cup and drains it cup faster than it can fill causing massive amounts of air in the system.


Suffice to say, a pair of my lift pumps will do better as they do not need to bypass to regulate, and do not restrict in the event of stall. They also don't sound (very quiet) like a giant can opener. :eek: I will also have a filter/pump setup available soon for those who want an aft mounted filter.


I'll also add that the Dmax system doesn't really seem to mind air. I can drop the tank, install my pumps and pickup, then start the engine without the pumps operational and it will idle away fine with a possible surge or two as it processes the large slug of air that I have just introduced. Since my pumps will not prime, I don't cut them on until the engine has been running a few minutes to help pull the air through the system.

[aceduramax]

Alrighty then, sounds like i dont need to go out and blow 600 bucks on something thats not needed then... thanks for the advice!!!

[Claven]

I put a 150 gph FASS on my truck and noticed a huge gain however, a regular pump, as previously mentioned, would have probably worked aswell. My problem was fuel loss just after a shift so all I needed was a lift pump but I like the returning fuel setup rather than just a pump dead headed, I'm not saying anthing is wrong with kennedy pumps it's just my personal opinion. I did have to put a bigger pick-up tube in the tank, because it would suck air in through the top of the pick up, and IS a bypass built in so if the pump stalls your truck will still run, it happened to me, and I can fill my truck when its running, no spillage.

[ 10-13-2005, 08:42 AM: Message edited by: Claven ]

[Mark Heiken]

Claven, can you explain your huge gain? Was it milage, performance or both?

[Claven]

My truck would fall on its face just after a shift and would take a second to recover, also at the top end, around 80 - 120 mph, the truck would jerk and stumble. After researching this sight I came to the conclusion I was running out of fuel. Now it pulls hard all the way to the top with no falling or stumbling. I've also noticed alot less smoke. Dropped me from 13.8@98 to 13.3@108

[aceduramax]

Alright, so far from what ive heard, the fass system only really helps out heavily modded trucks... and doesnt really do much for stock trucks with just a juice... so maybe i will have to do some more playing with my truck before i do the fass... thanks guys...

[Kennedy]

Lift pumps are good idea for any Dmax. What is a bad idea is the bypass regulator returning excessive amounts of fuel to a point other than the cup. It's either that or shut it off below 1/4 tank :rolleyes:

[Claven]

You are right when I first the installed the pump I left the factory fuel pick-up connected and when I got down to 1/4 tank it would suck air, but the truck would run fine. I disconnected the pick-up and replaced it with 1/2" opened end hose, now it works perfect.