Fuel system by pass filtering?

[Yachtcare]

I'm getting ready to install a FASS fpr 1001 pressure regulator, between the stock FFM and the DB2 IP I have recently installed, to get the pressure from the Cummins lift pump back down to a sustainable 9psi. Don't know what it pushes now, but is rated at around 14-17psi IIRC.

The FASS includes a bypass for excess fuel to be returned "to the tank", and the instructions specifically mention that plumbing it back to the vehicles stock return line is not recommended. Said return line is a 1/2" NPT opening at the bottom. So I plan to put a 3/8" barbed fitting in there. Then the question remains where to plumb the return fuel too.

I'm assuming that this fuel would need to be returned in a manner as the stock setup is, in a closed loop, so air cannot be introduced to the system.

I have a 10 micron Racor fuel/water separator mounted on the frame between tank and lift pump. I have installed shut off valves on both sides of the Racor housing to make element changes simpler, without much bleeding necessary. My thought is to take the return fuel from the FASS, and plumb it to a tee on the intake side of the Racor. This should draw the return fuel through the Racor, and just send it harmlessly back through the filters again. At least that's what I think.

Anyone see any flaws in my logic?

For overkill, I've toyed with the idea of a 2 micron element on another Racor mounted in the FASS return line.

 

[Will L.]

Possible drafting off the return line faster demand than the supply, as the return "loop" would have less resistance than from the main supply. If that occurs then you would aerate the fuel.

Also fuel running through the ip gets heated from pressurizing and the heat / reheat cycle could have negative affects: The lubricity of ulsd sucks already and gets worse with heat.

To return to the tank just a thru bushing into the top of the tank that is threaded both sides, or if cheaper threaded 1 side and you tap the other. a down pipe inside the tank a half inch off the bottom. Have you already tossed the fuel sock that's in the tank? If not now is the time to do it.

my 2 cents, which at current dollar value is only worth about 1/2 farthing.

 

[guybb3]

Or tap into the fuel filler neck.

 

[Will L.]

Or tap into the fuel filler neck.

The problem with that is when he truck is shut off if the truck is parked uphill, like in a steep driveway or off road. If the fuel from the return line side can drain, it can let air get back to the outlet of the ip causing havoc.

That's why the factory return line always goes down toward the bottom of the tank with the pick up tube. That's why he can't just "dump" into the tank, it needs to go down under the fuel level.

 

[Burning oil]

Can you route the return fuel to the inlet side of the pump? I did that on a WVO system I had. Not sure if you can with FASS??

 

[Yachtcare]

The problem with that is when he truck is shut off if the truck is parked uphill, like in a steep driveway or off road. If the fuel from the return line side can drain, it can let air get back to the outlet of the ip causing havoc.

That's why the factory return line always goes down toward the bottom of the tank with the pick up tube. That's why he can't just "dump" into the tank, it needs to go down under the fuel level.

That's what I recall. Return goes below fuel level so theres no air lock.

Figured keeping in a closed loop by returning to the fuel line behind the filter would keep the system air tight. So I wouldn't think aerating the fuel would be a concern, but maybe creating a vacuum that might collapse the rubber portions of fuel line could be a possibility? Or the fact that you cant compress liquids negates any concern of vacuum? A 2 micron filter in the return line might(?) restrict the return enough to stifle the vacuum effect (if any?) as well as serves to "polish" the fuel a bit more.

 

[Yachtcare]

Can you route the return fuel to the inlet side of the pump? I did that on a WVO system I had. Not sure if you can with FASS??

Wouldn't that defeat the purpose of the pressure regulator? Fuel enters reg, pressure is reduced and sent toward the IP, excess fuel that has been "regulated" out of the lift process goes out the bottom of the reg to be "returned".

Remember, I'm only using a FASS regulator, not the entire FASS system. Running a Cummins hfp 953 lift. FTB mod with 3/8" line from FFM to back of DB2 IP.

 

[Burning oil]

Maybe I missunderstand? You want a place for all of the return fuel thats not used by IP/injectors to go right? If yes thats after the need for regulated PSI to the IP, so returning fuel anywhere on suction side of pump will be good. Weather it go's to the tank or pump inlet I don't think the fuel cares, but would cause less airation if kept in a closed loop by returning to pump inlet.

 

[Yachtcare]

Maybe I missunderstand? You want a place for all of the return fuel thats not used by IP/injectors to go right? If yes thats after the need for regulated PSI to the IP, so returning fuel anywhere on suction side of pump will be good. Weather it go's to the tank or pump inlet I don't think the fuel cares, but would cause less airation if kept in a closed loop by returning to pump inlet.

We want a place for all the fuel not used by the regulating process of the FASS to go. The vehicles system remains untouched.

I may be misunderstanding as well. By "pump inlet" we are talking about where the regulated pressure from the FASS regulator is going to at the back of the DB2 IP(?) or the back(somewhere behind) of the lift pump(?). If we are returning the pressure that has been regulated out back to the IP inlet, assumably via a tee right before the inlet, haven't we simply added that pressure right back to the place we were trying to limit it at, in the first place?

Returning the bypass fuel from the FASS to the vehicles return line, is a no no, according to the FASS install instructions.

 

[Will L.]

On aerated fuel from the "t" system is a guess. creating low pressure or even vacuum on return of ip takes someone with WAY more knowledge than me.

I know from years of working with and for fuel production companies most #2 diesel starts to loose lubricity at 220 f. By 450 its lost as much as it can loose without molecular alteration (in the presence of oxygen). If you are adding any lubes to it then I wouldn't sweat it.

This was a problem Detroit had when they introduced the isc (iirc)engines in generator applications in the 90s. Worked ok in cold areas but hot climates it showed up problems. I was involved in a testing for 76 fuels with Detroit trying to figure out why their shortened injector life was happening. Took about 5 minutes to figure that one out. Before you run and grab the ir laser temp gun to see where you are at, the thermal loss from fuel through the line is too much to read. A tc inside the line has to be used. You could build a temporary reservoir with a probe sealed in it and run the loop with the pump wired on and run it for a few hours to see how warm you get.

Here is another thought: I like oranges. Ok, here is a relative one: if you were to dump into the filler neck like guy33b said, a simple one way check valve could solve the problem. Just by a good one and put it a foot or so the output is faced down hill so no debris could settle against it blocking it open.

 

[Yachtcare]

I know from years of working with and for fuel production companies most #2 diesel starts to loose lubricity at 220 f. By 450 its lost as much as it can loose without molecular alteration (in the presence of oxygen). If you are adding any lubes to it then I wouldn't sweat it.

Here is another thought: I like oranges. Ok, here is a relative one: if you were to dump into the filler neck like guy33b said, a simple one way check valve could solve the problem. Just by a good one and put it a foot or so the output is faced down hill so no debris could settle against it blocking it open.

I ALWAYS add TCW-3 spec for lubricity. An occasional shot of Power Service as well.
I like the check valve idea. Will give it more thought.

 

[Burning oil]

I think I just clued in. Your Fass pump needs to dump excess fuel. Returning it to suction side of pump would not be ideal then.
Seems like your going to have to do a custom return to the tank.

 

[WarWagon]

This is Overkill to the point it may not work by introducing more problems than it is worth. A DB2 already bypasses and flows a lot of fuel back to the tank. If you go over 5-7 PSI on the DB2 inlet the timing gets messed up as it is referenced to transfer pump pressure. The transfer pump regulator is referenced to the inlet pressure so you can float the housing pressure up by raising the inlet pressure.

The return line in the tank is small. So adding anything to the factory return line would further risk blowing the return lines off the injectors from pressure in the return line due to a small hose in the tank.

By-pass filtering is worthless as the damaging particle only has to get by the filter once to do damage depending on what luck you have as to where it goes. So it better be filtered the first time.

You may just want to get a 'smaller' lift pump rather than go through the trouble of a custom tank pickup and return. Not only do you need a big return, but, you will need a bigger pickup line to avoid boiling the diesel from excessive restriction on the suction side in the tank. All this power wasted to move and heat fuel back to the tank...

The return line is submerged not only to prevent air from getting into the system from sitting while parked - it prevents air from being aerated into the fuel from falling from a height in the tank where it lands.

When the fuel level gets low moving this much fuel for S&G's could cause a whirlpool to appear over the suction line and introduce air - that slower/less fuel movement wouldn't cause.

 

[Yachtcare]

This is Overkill to the point it may not work by introducing more problems than it is worth.

You may just want to get a 'smaller' lift pump

Perhaps the best advice (or admonishment?) yet.

In my zeal to retain a bigger lift pump, I created problems downstream that could be solved by just going back to a stock airtex E3158.

So a fresh E3158 is on its way, the FASS regulator is on it's waay back, and a slightly used Cummins lift will be on the market soon.

I'll install the pressure gauge between the FFM and the IP and call it a day.

 

[turbovanman]

The problem with that is when he truck is shut off if the truck is parked uphill, like in a steep driveway or off road. If the fuel from the return line side can drain, it can let air get back to the outlet of the ip causing havoc.

That's why the factory return line always goes down toward the bottom of the tank with the pick up tube. That's why he can't just "dump" into the tank, it needs to go down under the fuel level.

That actually isn't true, some or most have the return stop right under the mounting cap with an orange, rubber check valve. I just had mine out and its like that, look at pics people post up of their sending units, same thing.

Perhaps the best advice (or admonishment?) yet.

In my zeal to retain a bigger lift pump, I created problems downstream that could be solved by just going back to a stock airtex E3158.

So a fresh E3158 is on its way, the FASS regulator is on it's waay back, and a slightly used Cummins lift will be on the market soon.

I'll install the pressure gauge between the FFM and the IP and call it a day.

Honestly, stock replacement turbo pumps are garbage. I just installed a new system on the van and simply tee'd into the tank vent line like so-

 

[Burning oil]

Perhaps the best advice (or admonishment?) yet.

In my zeal to retain a bigger lift pump, I created problems downstream that could be solved by just going back to a stock airtex E3158.

So a fresh E3158 is on its way, the FASS regulator is on it's waay back, and a slightly used Cummins lift will be on the market soon.

I'll install the pressure gauge between the FFM and the IP and call it a day.

Well slap me on the forehead :slap: I think sometimes we want to help someone with what they are wanting to do that the obvious is overlooked.

 

[Yachtcare]

Well, went to purge the system, and go for a start up today. Found the brand new airtex is dead on arrival.......Back to the drawing board.

Thinking of trying a cheap gas style regulator behind the Cummins lift.

Since it's return fuel from the regulator, and not the IP itself, I think the check valve at the tank vent, or variant thereof will work out. The fuel to the IP and return to tank is still a closed loop.

 

[Twisted Steel Performance]

I'll jump in here with my worthless info pertaining to this as my setup is just like what some say won't work...

My FRC-10 puts out 15psi, I use a cheap 70$ regulator and tee'd into the return line on the frame, it's been like this close to 1 1/2 years now, I haven't blown any lines, haven't had not a single problem as of yet..

I did pull the return line off afterwords to see how much flow or psi there is in the return system and there isn't as much as you would think... I'm no expert here but mine works like I wanted it to....

 

[Twisted Steel Performance]

This is the regulator I am using.... 12-803BP Holley Bypass Fuel Pressure Regulator Return

ebay item # 230903675937

 

[Yachtcare]

Thanks SC.......Will see if I can find one local, then head to the bay.