I thought i'd take a few photos since i've assisted in the changing of fuel pumps about 4 times this week... start with the back seats out if its a sedan or coupe
Tools required:
No.2 philips screwdriver
6mm blade screwdriver
long nosed pliers
8mm socket, 1/4" is best
side cutters, butt crimp terminals, crimping tool
cable ties
Step 1.
Locate factory fuel pump location, usually in the boot drivers side. Remove the cover by taking out the 4 philips No.2 screws
Step 2.
Use the long nose pliers to remove the clips holding the hoses on and push them aside, the fuel feed line is usually a clip-lock fitting; use pliers to hold clip and wedge with flat screwdriver. Use the screwdriver to wedge the plug clip and unplug also
Step 3.
Remove the 8mm bolts being careful not to drop them. Lift the pump out adn tilt it slightly to the side so the level float does not get caught
Step 4.
Take complete assembly and work outside. It is a good idea to use the metal cover over the tank to stop dust getting in. Use pliers and move clips aside and slide off stock pump - the aftermarket ones fit on in the same manner. For the Ver 3/4 WRX and earlier models with the fatter style pump you need to cut the wires and crimp them to the aftermarket pump. Ver 5/6 WRX and above the factory plug fits straight into a Walbro pump (not sure if other pumps are the same, but Walbro seem a popular aftermarket choice). Use cable ties to hold the wiring in place and stop it rubbing against the sharp edges of the mounting bracket. I used a large cable tie at the base as wel to hold in place as the stock rubber bung was too big.
Here is a picture of size comparison between the stock V3/4 pump and the aftermarket one:
Step 5.
Drop the pump back in. Put the 8mm bolts in first and then the hoses and clips, the feed line should lock in place with a click - give it a few pulls to ensure a tight fit (the earlier models V1/2 use a scew type hose clip for this - and the feed line is the middle one). Make sure it's plugged in and put the cover back on... and seats back in