Fuel Supply and Return Reversed? Options

[s13u74cr4]

I believe the PO of my 914 reversed the supply and return on the fuel lines when he swapped in SS lines. From reading other posts and diagrams the larger should be the supply I think. Believe this is backwards?
Zip tie is me trying to figure out what’s happening and get a decent photo and failing.

[rjames]

What's with the plastic T?

[Literati914]

What's with the plastic T?

If you're talking about the "Y" (IMG:style_emoticons/default/biggrin.gif) , that's the return splitter that sends fuel back to the pump and tank - everything attached to it should be the smaller hose/pipe.. which from these pics looks like it's mistakenly going back to the larger tunnel pipe. So that would be incorrectly routed if I'm not mistaken.

To original poster: I think the holes/grommets at that rear firewall are sized specifically for the large vs small tunnel pipes. I also believe the pipes are mixed up, iirc.

[r_towle]

Supply comes from the largest fitting on the bottom of the tank.
That fitting has a screen inside to prevent large rust and dirt from getting sucked into the engine fuel supply

From underneath, you can see it is the larger diameter tube.
From there it should go to a fuel filter…up from in a 75/76 car, or in the rear for earlier cars.

Filter is before the fuel pump to protect the pump.

[s13u74cr4]

The larger SS line goes into that “Y”. For sure that plastic piece needs to be replaced.
I have not traced to the tank yet so no idea if that is correct. Any easy way to tell without taking too much apart?
The small line does go to the fuel filter then the top port on the fuel pump which is correct. Cramped and hard to see here.

[windforfun]

Can you get a "Y" piece that isn't plastic?

[Literati914]

The larger SS line goes into that “Y”. For sure that plastic piece needs to be replaced.
I have not traced to the tank yet so no idea if that is correct. Any easy way to tell without taking too much apart?
The small line does go to the fuel filter then the top port on the fuel pump which is correct.

Like I was saying - that part is wrong!
Your Y has a large SS line attached - that is INCORRECT. All connections of the Y should be small diameter line. The Y is for returning fuel to the tank from both the fuel pump and the engine (via the small diameter SS line).

BTW, the small SS line (return) exits the tunnel at the front and attaches to the pipe fitting that is closest to the center seam of the fuel tank. You're able to see that thru the round port if you jack up the front and crawl under it with a strong light. The fitting furthest from the fuel tank's seam is the larger supply pipe and contains a mesh filtering sleeve inside the tank. [except for '75-'76 cars .. I think the nipples off the fuel tank are both 8mm in their case]

If you find the above to be the case, then good - all's well at the front end. If you find the opposite to be the case, it could be that a PO left the mesh filtering sleeve off and crossed up the fittings (if that's even possible), but the mesh filter sleeve will only fit into the larger fitting hole furthest from the seam.

Fuel Filter: Sorry but I believe your fuel filter set up is also wrong. Looks like you have a Mahle KL11 which is 8mm on both sides iirc. It will work but should come from the larger SS pipe and connect via a reducing hose. What the stock had was a square filter that had 8mm inlet/outlet but utilzed a "reducing hose" (pn#914 356 525 00).. which would only work if the larger SS pipe is the feed line, as it should be. Large SS line exits the rear firewall, reduces with that short hose into the filter, and then on to the 'S' port of the pump (suction).
The D port of the pump is 'direct' pressure to the engine, R port is the 'return'.
HTH.

[s13u74cr4]

The larger SS line goes into that “Y”. For sure that plastic piece needs to be replaced.
I have not traced to the tank yet so no idea if that is correct. Any easy way to tell without taking too much apart?
The small line does go to the fuel filter then the top port on the fuel pump which is correct.

Like I was saying - that part is wrong!
Your Y has a large SS line attached - that is INCORRECT. All connections of the Y should be small diameter line. The Y is for returning fuel to both the fuel pump and the tank (via the small diameter SS line).

Ah, sorry, meant after the incorrect small SS line exit, it flows to the filter then the top port of the fuel pump which I think is correct.

Dang, wrong filter too, good grief.

Can you get a "Y" piece that isn't plastic?

I hope I can find something non plastic there. Seems a shame to have replaced it all then left a weak link in.

Appreciate the tips.

[Literati914]

Dang, wrong filter too, good grief.

I could be wrong about the filter.. I mean, you have it hooked up an aren't reporting that it leaks.
EDIT: the reason that the Mahle KL11 is working in your case is because you are mistakenly using the small SS pipe as a feed, 8mm pipe and hose work with the KL11 filter.

Can you get a "Y" piece that isn't plastic?

I hope I can find something non plastic there. Seems a shame to have replaced it all then left a weak link in.

Appreciate the tips.

Lots of options when goggling - ".. 5/16" Y fitting.."