F-250 6.7 Powerstroke low fuel pressure

So, switched fuel filters today on my '16 F250 6.7 powerstroke. Took it out for a drive and got low fuel pressure flashing and it threw a code. No need for anyone to try and figure this out. I fixed the problem. I didn't have the frame rail filter housing tight enough and apparently it was sucking air. However, here's my question. The fuel is pressurized in the tank by the pump. It is then sent to the frame rail filter then to the filter on top of the motor . Why, if the rail filter isn't tight enough, is the system sucking air and not spewing out fuel? Doesn't make any sense.

P.S. I HATE MODERN VEHICLES!

ttt

It's because it doesn't have a pump in the tank. The frame mounted filter is also the in line pump. That filter filters diesel from the tank feeding the pump and then the top filter filters the diesel from the pump to the injection pump. Least that's what they taught in Ford diesel class.

Pressure is from the injector pump on Diesels, isn’t it?

its a ford! they had a better idea!

The fuel filter assembly has a pump integrated into it. It's just a "lift pump" that sends fuel to the engine. The engine itself had a system to then pressurize the fuel to a much higher pressure for injection into the cylinder.

Modern Diesels tend to be complex.

It was used too much when it was new.

the lift pump in diesels runs at about 8# pressure, the pump was pulling fuel through the filter, so it was sucking a bit of air, but still moving fuel.
RR

Humph! That answers that question. Thanks. It sounded like it was coming from the tank but kind of hard to pinpoint when you are sitting in the cab turning the key and I just assumed it was in the tank since most gas powered cars have it that way.

I understand finster. The sound can be deceiving. I'm pretty sure they told us in school that a electric pump inside a diesel tank was just a bomb waiting for a place to go off but then I'm pretty sure dodge put thiers in the tank so I don't know. I know there is a reason why Ford doesn't put it in the tank like on gas vehicles because in tank is easier for assembly so there must be something to it.

Yea, I don't know why they ever started putting pumps in tanks to begin with. It was always a stupid idea as far as I'm concerned. I'm glad mine is on a frame rail. I used to replace fuel pumps on cars at my fathers garage back in the day. I was always a little nerve racking dropping a tank with fumes all over the place. Even if you could siphon most of the fuel out, you never got it all out. Naturally, 9 out of 10 times, the customer had 1/2 to a full tank of gas also. I know a guy who was burned horribly back in high school welding under a car when the tank went up. I saw him decades later and he was still getting skin graphs. He never did look the same obviously.

FASS all the way