____Car is a 1990 Civic Si. All stock____

After I fill up my tank it acts as though it runs out of fuel at ~ 210 miles on the odometer (approx. 7 gallons of fuel consumed).
It does it at the exact same time every time. I have dropped the tank, and it is visibly clear and does have the remaining 3 or so gallons in it. The fuel pump is in place and the sock is on correctly. I would not think that it is the fuel pump since it is new and it happens at the exact same fuel level every time. I've had the tank out 3 times now and everything is correct. Again- new fuel pump and new fuel filter. Car runs perfectly when tank is above ~ 3.5 gallons.

Basically, my car acts like it's out of gas when there is roughly 3 gallons left in the tank. What's the problem?

 

is your new fuel pump a factory unit, or aftermarket?

i have seen in one case (non honda though) that the sump had a hole in it and it acted this way. think of it as having a soda that you are drinking with a straw, only the straw has a hole in it 2/3 the way down, it will suck fine until you get to that point, then it sucks a mix of air and gas (because of the gas sloshing around). making it seem like its running out of gas.

i'm not saying that is your case, but its possible.

 

It is a new Carter (aftermarket) unit. They make good pumps, I've never had a problem with them.

We actually put this Carter in because the original setup was having this same problem and we just assumed the pump was going out. Now the new pump does the same thing!

Your idea makes sense but I'm not quite sure I understand what you mean by "sump"

The pump just drops down into the tank, and sits a few inches above a baffle of some sort. I'm not sure which part of the "straw" could have a hole or problem in/with.

This makes the most sense so far - nothing else adds up.