Engine/Transmission (1998.5 - 2002) Parallel Stock/FASS Install-- a long post

[MKizziah]

Getting preped to install FASS. I've been told by many that you can't or it's not possable to install a FASS in parallel with the stock elect. LP. Never been one to accept those answers, here's what I came up with.



I would appreiciate any feedback or thoughs on this!!



Theory of Operations:



Plumbing:

Simply by using 4 inline check valves and 2 tees you can isolate fuel flow from the non-operating LP automatcally.

How:

Tee the tank suction output, place a check valve on each side of the tee. One side feeds the FASS other side feeds the line to the stock LP. Then place a tee on the input side of the stock filter. ON the Filter Tee place a check valve on each feed from the pumps.

Note: The check vavle flow direction is from tank to stock filter on all check valves.



How it works:

The suction from the operating pump closes the check valve that feeds the the non-operating pump at the tank tee. Conversely the fuel pressure feeding the filter closes the check valve on the tee to non-operating pump at the filter. Thus the fuel pressure from the operating fuel system closes and isolates the non-operating system.



Electrical:

Disconnect the wire that feeds relay control signal from PCM to stock pump.

Connect the PCM side wire to a SPDT switch (common connector). Run a wire to stock pump connector from the switch. ( A pole of switch). Run a wire to FASS pump relay connector from the switch. ( B pole of switch). Switch in the A posistion runs stock pump, B posistion runs FASS pump.



Guess if you use a Single-Pole Triple Throw switch, you could have C pole not connected to anything. . That would keep the wife or anyone else for that matter from starting your truck . . lol



Pros:

Allows you to utilize the stock filter (more is better), WIO sensor, in the stock system while running the FASS.

No more fuel system LP failures and or FORD incidents.

Switch between fuel systems "in cab".

Cheap Anti-Theft system.



Cons:

Bleeding the fuel system may be an adventure.

May delay starting by the fuel pressure having to build up to close check valves. I'm thinking minimal at best.



I will get some diagrams up on the post very soon. (soon as I figure out how)



I welcome all discussion or ideas pro or con.



TIA

Cheers,

MAtt

 

[MKizziah]

Added Diagrams

Here's the diagrams. Plumbing and Electrical

 

[snowracer69]

Looks good, but why run a switch to decide which pump to use? I didn't take the time, but I'd bet you could find a pressure opperated hobbs switch that would make the LP come on automatically if/when FP drops below a set point, much like my RASP is configured. Also, you will always be losing pressure from the pumps as they have to push through the check valves to get to where the fuel needs to be going.

 

[MKizziah]

Thanks for comments

hi snowracer,

I probably mislabeled the post. I wasn't really thinking of running both pumps at the same time. More of an "online backup" for the FASS if it fails. Thus the "in cab" switch.



I'm thinking, Oversizing the check valves should counter any flow loss due to friction loss of the check valves. http://www.microchek.com/html/products.html



Do you know of any source . . other than dodge. . for electrical and quick disconnect connectors??



Thanks for your comments

Cheers,

Matt

 

[JFinke]

You should only need to run one check valve on each pump and the one after the pump before the tee at the stock filter would be the best one to use. Jake

 

[Todd T]

why dont you just install a stock LP upstream of the FASS system. you can pull fuel through the stock LP if its not running. that way you would have one set of plumbing and less chance of a part failure out of those checks valves and such.



better yet just get some quick disconnects for hydraulic lines and make it so you can easily uncouple the pickup and couple in the stocker and be on your way. just extend the power on a plug back there for when its needed.



point being. . you CAN pull through the stock LP's