fuel drain-back cure ?

[jethro]

my motor runs like buttery silk so far. (that's good!)
I am currently coming out of the f-350 center tank (which has NO lift pump- only a float and sender)
up to the frame to a 150 micron screw-off strainer (quart sized can) then forward to 2-nd gen dodge-cummins piston
pump running off crankshaft. I have NO lift pump.
It primes easy enough by just operating the plunger on the mechanical pump. When it sits overnight though it takes about 3 attempts to get a start. It is about 10 feet from the engine to the tank.
One solution would be to put in a fairly big check valve on the suction line just above the tank. would want the valve to open
at as low a pressure as possible. My suction line is 3/8 copper(with 1/4 return).
Another way would be to use some kind of small centrifugal pump which has some internal clearance- but that it would make just enough positive pressure to gently push the fuel forward- but at the same time have enough clearance to bypass some
so it wouldn't be angry if it wasn't passing much fuel. Also if this pump failed it wouldn't represent much fluid resistance
to the mechanical pump sucking through it.


I suppose I could also do some kind of 12 volt electric solenoid valve which would close as soon as the key is shut off.
Could be wired in parallel with the engine's electric fuel shut off valve.
But if that fails- engine stops.

Note: I have not done a real leak check on the lines and strainer. I can take the line off at the tank and engine pump-
add a little air and do a soapy water test ????? I guess I SHOULD do that first before I decide there is a real problem.


do I need some kind of expensive lift pump ?

Tim

[fatty]

That's how all Dodge 12 valves are from the factory. You must have a fuel leak some where that allows the fuel to drain back.

[jethro]

I will rig the air and soapy water bubble test tomorrow !
Sounds like I may get away without a pump. I like that !!!!!!
Thanks for the reply ! Im new at Cumminses (to quote elmer fudd)

tim

[DMan1198]

One thing to note is that piston pump is considered a lift pump. it is supplying positive pressure to the injection pump (usually 12-18psi)

[CumminsPower59]

I will rig the air and soapy water bubble test tomorrow !
Sounds like I may get away without a pump. I like that !!!!!!
Thanks for the reply ! Im new at Cumminses (to quote elmer fudd)

tim

I am not tracking how the soapy water will work.

If there is a drain back issue, inspect all of your fuel lines and connections. An easy way to find a leak is to pressurize the system starting at the tank, if there is a place before the lift pump that could be sucking air, then fuel/air will be coming out. 2-5 psi is a good start

[Gots_a_sol]

I will rig the air and soapy water bubble test tomorrow !
Sounds like I may get away without a pump. I like that !!!!!!
Thanks for the reply ! Im new at Cumminses (to quote elmer fudd)

tim

I am not tracking how the soapy water will work.

If there is a drain back issue, inspect all of your fuel lines and connections. An easy way to find a leak is to pressurize the system starting at the tank, if there is a place before the lift pump that could be sucking air, then fuel/air will be coming out. 2-5 psi is a good start

Sounds like he is going to pressurize it then spray soapy water on the lines/connections and look for the bubbles.

I've heard that leaks can be small enough to not leak fuel out, but to let air pass, so can't always count on looking for the wet spot

[PToombs]

If you pressurize the tank and have a line leaking air the fuel will leak out at that spot, no need for soapy water.
Is that a p-pump engine? If so, check the fuel heater where the wire plugs in, on my 2nd gen I had awful hard starts and found that was the leak. I had an electric fuel pump at the tank and had the return pinched off, I had 30psi on it and no leaks. When I unplugged the heater it made a shhhhhhhh noise and the fuel sprayed out like a SOB.

I heard copper is not good with diesel fuel. Had a buddy working on a chipper with a fuel issue, turns out the pickup in the tank was copper, and it was coated with a black crust. He ran a wire up the tube to clean it and it ran better.

[CumminsPower59]

I second ditching the copper. Get some marine grade, bio-diesel compatible rubber hose or plastic line. Too easy.

[jethro]

The only pump is on the side of the engine.
I was going to remove the rubber line which goes on top of the tank and remove the line which goes on the engine pump-----
pressurize that with air (after blowing out the fuel) and bubble check that part.

Now that I think about it- I suspect the leak might be at the pipe thread fitting in the body of the piston pump.
Pipe threads can get a little bur somewhere and be hard to make airtight. I suspect that before the other junctions.
I have 2 of those (pipe nipples hose barbs) on the side of the aftermarket strainer too.

I will research coppers compatability with diesel. easy to change if I need to !

Tim

[CumminsPower59]

Did you use any sealant on the pipe threads when you installed the fittings? I am probably wrong to do so, but I always use either thread tape or pipe "dope".

[jethro]

yes- I used the Teflon based paste and careful not to get it on the inside. I am a little afraid to use tape in a fuel system.
I have discovered tape pieces before in fuel systems when taken apart.