Can I install a inline fuel pump on my 03 ford expedition?

I can't afford a OEM fuel pump

No. Because the one in the tank is a "pusher". A inline pump that you want to install is a "puller". But it will not be able to pull fuel from the tank with the pusher still in the way, blocking the line. You would have to remove the pump in the tank first. Then you are back to square one.

Well, like the other responder said you can, but you'd have to get rid of the old one inside the tank. The part that holds the fuel pump & drops down into the tank is called the 'hat'. They make 'hats' with no pump so you can use an external pump, but I doubt that it would be cheaper that a replacement pump. The guys who put external pumps are the drag racers, & they do it because the internal pump can't move enough gas fast enough for their high-powered engine. So a set-up for them is well over a grand & will pump your tank dry on 3 to 5 minutes…

Nope the inline pump is not strong enough, won't hold the correct pressure The fuel pump in your vehicle is capable of pressures around 100 or more PSI.Newer direct injected motors have fuel pressures in the 1000 PSI range Its regulated down just before it enters the engine to be burned. The inline pump will most likely far less than your factory pump Your also risking a fire by tampering with your fuel lines I know its expensive to replace But you can't safely or reliably by-pass your intake pump for some inline unit that was not designed for want you want to do with it You need to buy the OEM replacement