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Pressure (p.s.i.) in the Fuel Return Line of Series II 3800?
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Author:  StraTact [ Thu Jan 11, 2018 11:00 pm ]
Post subject:  Pressure (p.s.i.) in the Fuel Return Line of Series II 3800?
Does anyone know what the expected pressure (p.s.i.) should be for the fuel return line that goes back to the fuel tank? I don't want to have a burst hose if I choose a 40 p.s.i. rubber fuel hose instead of a more expensive 100 p.s.i. fuel-injection rubber fuel hose.

Here's why: While replacing my fuel tank (and straps), fuel pump, and sending unit, I had to cut all three fuel lines (i.e. fuel supply line, fuel return line and fuel vapor return line) about midway underneath my right rear door, because they were badly corroded. Because of the cold/snowy/slushy NH weather we're having now, I'm planning to temporarily replace these lines with about 3 feet of rubber hoses connected at the fuel tank with quick-connect adapters and hose clamps, and the metal fuel lines at other end with just hose clamps. I think this would be easier to perform in this lousy weather than installing nylon tubing instead of rubber hose. When winter is over and the weather is nice, I plan to replace my entire fuel lines again, from the tank all the way to the engine, with nylon tubing.

So, temporarily, I'm planning to use 250 p.s.i. 3/8" I.D. Buna-N fuel hose for the fuel supply line because my Spectra Premium pump is rated between 72.5 -101.5 p.s.i. pressure. I'm also planning on using 40 p.s.i. 5/16" I.D. fuel hose for the vapor return line because I don't think there's much pressure there from fuel vapors.

What I'm not sure about is whether I need to use expensive high-pressure 100 p.s.i. fuel-injection hose for the 5/16" I.D. return line, because I don't know what to expect for pressure (p.s.i.) in the fuel return line.

Does anyone know?
Author:  96 SSEi [ Fri Jan 12, 2018 4:05 am ]
Post subject:  Re: Pressure (p.s.i.) in the Fuel Return Line of Series II 3
you should be fine - its just return line - its under 40psi
Author:  StraTact [ Sat Jan 13, 2018 2:03 am ]
Post subject:  Re: Pressure (p.s.i.) in the Fuel Return Line of Series II 3
Are you saying that the Fuel Pressure Regulator should keep the return line under 40psi, regardless of the pressure from the supply line of the fuel pump?
Author:  RJolly87 [ Sat Jan 13, 2018 4:01 am ]
Post subject:  Re: Pressure (p.s.i.) in the Fuel Return Line of Series II 3
I am not aware of anything that would restrict the flow and cause pressure. I believe it just drains straight back in to the tank.

The fuel return can be envisioned like a water flowing from a water faucet (fuel pressure regulator). There is no real pressure until you try and restrict the flow.
Author:  96 SSEi [ Sat Jan 13, 2018 11:37 am ]
Post subject:  Re: Pressure (p.s.i.) in the Fuel Return Line of Series II 3
StraTact wrote:
Are you saying that the Fuel Pressure Regulator should keep the return line under 40psi, regardless of the pressure from the supply line of the fuel pump?


I had a leak and it was a slow drip at pressure/running - if it were at 40psi, it would at least 'fan' at the leak.

ours prob work similar to this ......http://www.nukeperformance.com/wp-conte ... age021.jpg
Author:  StraTact [ Sat Apr 07, 2018 11:55 am ]
Post subject:  Re: Pressure (p.s.i.) in the Fuel Return Line of Series II 3
All my starting, stalling and hesitation problems finally went away after I replaced my fuel tank, fuel pump, sending unit, and my fuel filter.

I also replaced all 3 fuel lines with Dorman nylon tubing and Dorman barbed fittings (compression and quick-disconnect), from the fuel pump to about a couple of feet in front of the fuel filter. No leaks! 3/8" and 5/16" Nylon tubing was very inexpensive compared to high-pressure rubber fuel-injection hose, and easy to press onto the barbed fittings, once I figured out how to do it.

My car runs great now!

So, my new fuel pump's 100 psi pressure made the difference.

Thanks for all your suggestions!
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