So, I'm well aware that there is an arrow on the fuel filter that designates which way it is supposed to flow. However, when I got under my truck to change it the other day, there was a larger line, and a smaller line running side by side. The fuel filter is in the smaller line, as I'm sure everyones is. Isn't the small line the return to tank? And if so, I thought the fuel filter on these was in the feed line, so it could be filtered before getting to the injectors. Will the truck still run if the filter is instaled backwatd? I would think so, just not very well.

So if the fuel filter is in the return line, then obviously the arrow should point to the rear of the truck when installed, correct?

Doug

 

The arrow points to the front of the truck. Also, the inlet is larger than the outlet.

 

Well see that's what I thought too, but the one I took off had the arrow pointing toward the back of the truck, so that's how I installed the new one. The truck seems to run ok, but maybe it's not running as good as it should. If the small one is a supply, then what is the larger line next to it for?

 

Been too long. I don't remember what that line is. Seems like it was a vent line or something. I don't see how the smaller outlet side of the filter is sealing off, going into the larger clip and vice versa. How is the larger inlet side of the filter going into the clip on the engine side. Weird.

 

My engine knowledge is from 4.6 mustangs, but I am sure the 5.4 is the same.

These engines no longer have a return line. The computer only calls for precise amount of gas the engine needs, instead of just providing a steady fuel pressure. This keeps the gas from having to recirculate which heats it up, and I am sure hurts performance and emissions.

I did my fuel filter recently, dont recall an additional line down there but I may have missed it.

 

Yes, there is a larger line behind the fuel filter line.

 

Look at the pics, especially in post 5. You can see the larger line behind the filter line.

https://www.f150online.com/forums/ar...-pictures.html

 

It appeared to me that both sides of the uninstalled fuel filter were the same OD. Mine was, and is now installed in reverse of the picture on the other thread, and the truck seems to be running ok. I'll change it and see if it makes any difference in performance and gas mileage.

Also, now that you mention it, I have known for a long time that most new cars use a variable output fuel pump system. I was just kind of perplexed by the whole arrangement since the filter appeared to be in backwards

Doug

 

The smaller line with the fuel filter is a high pressure fuel supply line and the filter arrow is direction of flow, to the front.

That larger line also has the connectors on it but it is NOT a high pressure fuel supply line. It is part of the vapor containment system.

Squirrels ate a 4 inch section out the top of mine, but they just nicked the fuel supply line.

Fuel flow is marked so that maximum use of the element is possible. Look at a fuel filter element sometime, it's round and usually pleated material. The pleats open up on the outerside, and are closed up on the inside. Dirt brought in comes with the supply side so they mark the filter to expose the outer side of the element to the fuel with dirt, thus exposing more surface area with open pleats. Should be clean fuel coming into inner side of element and being pushed on to the engine.

Even the non pleated style elements made up of material with many many holes and passageways like foams have greater surface area on the outside when bent into a circle.

 

you installed your fuel filter backwards.

do not reverse it though... you will be putting the dirty side on the engine-side of the system and wash all the dirt into the engine.

Buy a new one and put it in the right way. You will probably be OK to run it backward for awhile since the element works either way. The filter might not be quite as efficient backwards though.

 

Yeah, that's what I ended up doing. I stopped and got a new one on the way home from work because I was scared that might happen. Funny thing is though, I changed it out with the correct orientation on the new one, and didn't notice much difference, if any, on the butt dyno. It ran ok for the most part even those it was backwards for who knows how long. Oh well, maybe by some longshot my MPG will improve a little.

 

I wonder if it has to do with the strength of the filter media... I know on furnace filters there is a wire mesh on the back side of the filter... putting that in backward could pull the filter off the mesh and rip it.

Perhaps a fuel filter is the same kind of setup - the filter media is stronger in one direction.

If so, it will work either way till it rips or tears. Hopefully you got lucky and it never ripped.

Either way, if they take the time to mark the flow direction then it must matter. I think you made the right call in changing it right away.

 

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The new fuel filter does more to make life easier for the fuel pump thus allowing it to live a long normal life than making better fuel mileage.