Can't keep fuel equal in tanks.

[Rawze]

(02-08-2023 )TerryB Wrote:  No, the Fass return was going to both tanks also. Went from pump to splitter to tanks. The splitter that was used looked just like the splitter used on return line. I'm gonna change all that and see what happens.

I thought I would point out, for people reading this thread.. that the fass fuel system has no actual benefit to the engine or truck whatsoever unless someone is trying to destroy their engine trying pre-load the engines fuel pump to make 800+ horsepower. -= I.E.> It does absolutely nothing but to make the fuel mileage slightly lower (by a few tenths) otherwise. The engines existing fuel system already has more than adequate ways to keep air out of the fuel already. This especially if it simply has a davco filter on it.

Unless something is damaged on the fuel system that would aerate the fuel, any real issue should simply be fixed instead of trying to cover it up with an after-garbage fuel pump device that is sold to the masses with false promises and exaggerated claims. I.E.> Things like cracked fuel lines or cracked pick-up tubes in the top of the fuel tanks, etc. should always be repaired properly instead.

Personally, unless someone is one of those power hungry freaks that likes to abuse and shorten the h#ell out of engine life with their $40,000 commercial engine, using big power to race up every hill like a fool, then that system and device does not even belong on the truck at all. Removing it would be the best thing to do, and not trying to make it work so that it can cost you about a thousand bucks in fuel mileage loss each year.

[TerryB]

I don't know the reasoning as to why it was installed in the first place, it was on the truck when I bought it. I do know the engine programming hasn't been messed with and everything is stock. I have considered replacing the Fass with OEM pump but I don't know if that has anything to do with my fuel leveling problem. About to find out thou.

[snailexpress]

I spent 2 days searching for Cummins document i had read 5-6 years ago about fuel system. Unfortunately didn't find it yet. The document says - fuel return lines should be below fuel level in fuel tank. So, stand pipes must be in both tanks. Once fuel system is primed and air purged the fuel will stay in system unless you have air intrusion in some place. Than fuel will drain back into tank and air get in the system. Submerged return lines works as equalizing device and to prevent fuel aeration. Return fuel will flow into tank with lower level. When engine is off return lines interconnection works as siphon to transfer fuel in lower tank.
Will continue to search for you.

[Nostalgic]

My Pete has a splitter on the return. The suction is just an open tee. Engine off, the suction is what siphon/equalizes the tanks. Of course if the truck is parked leaning, more will go to the lower tank.

A cracked return tube can cause one side to fill more than the other since there isn't any static pressure on that side.

[TerryB]

(02-09-2023 )snailexpress Wrote:  I spent 2 days searching for Cummins document i had read 5-6 years ago about fuel system. Unfortunately didn't find it yet. The document says - fuel return lines should be below fuel level in fuel tank. So, stand pipes must be in both tanks. Once fuel system is primed and air purged the fuel will stay in system unless you have air intrusion in some place. Than fuel will drain back into tank and air get in the system. Submerged return lines works as equalizing device and to prevent fuel aeration. Return fuel will flow into tank with lower level. When engine is off return lines interconnection works as siphon to transfer fuel in lower tank.
Will continue to search for you.

Thank you for this response! It's good to know that at least I was thinking correctly about how the system is supposed to function. I'm really hoping the open port on the pump return was the problem.

[TerryB]

Well, I'm about to throw in the towel on this deal. The last thing I tried was eliminating the return lines going from the electric pump to both tanks. I plumbed the pump return in with the return fuel coming from the engine. Did it right at the back of the engine, was really quite simple to do. So now all the return fuel goes through 1 splitter valve and to the tanks. I'm still over-filling the right hand tank. The fuel level sensor is in the right hand tank. When running down the road you can see the gauge slowly creeping up. Stop and check the tanks, yep the left tank is considerably lower than the right. Here's something that's different. Now, with the engine shutoff the tanks will equalize. It wouldn't do that before. I think that's because before the pump return fitting on the tanks did not have a stand pipe. I think this was preventing the siphoning effect to take place. But, they still won't stay level with engine running. Another strange thing, after replumbing everything, the engine runs much smoother at low idle....how can that be possible?? I don't know...the only thing I can think of is when the return fuel from the pump was splashing in the top of the tank before, that was causing air bubbles in the fuel?? I don't know, but it is noticeably smoother when setting and idling. So, I'm installing valves on the tanks and gonna try and control return fuel this way. I hate when something doesn't work as designed, but I've replaced everything on the return and supply sides. Hoses, splitter valves, fittings, vents. Hoses are exactly the same length, same height when installed. The only other thing I may still do is reinstall OEM pump. But I don't see how that's going to change my problem.

[tree98]

Why not tear that fass the hell off and put it all back to stock?

[TerryB]

(02-22-2023 )tree98 Wrote:  Why not tear that fass the hell off and put it all back to stock?

Probably will, but will that fix my problem? I've waisted enough money already trying to fix it, might as well include pump also.

[hhow55]

Could it be possible that the standpipe in the tank that has higher level of fuel be broken off, or have pinholes ?