Walbro Fuel Pump for 2008 -11 STi/WRX/LGT Install:
11.) Grab the plastic stopper from the stock fuel pump and retrieve the O-Ring from the pump assembly and place them like shown below.
12.) Remove any paper towels from the housing and shove the pump into the shaved housing until it bottoms out, if it doesn’t seem to go in all the way you haven’t shaved the housing down completely. Touch it up and try again.
13.) Place the big snake hosing assembly back over the fuel pump making certain that all original o-rings are back in their appropriate holes. It should look something like this since the filter has not been installed yet. You do not want to put the filter on until the snake hosing assembly is installed since it’s a difficult to get to the compression washer.
14.) Grab the stock filter and compression washer and re-install to the Walbro. This can be tricky, I use 2 small flatheads to push and hold.
15.) Plug in all connections to the fuel pump and housings. Take the upper portion of the housing and mate it with the bottom (it’ll take some force). Toss it in the car in the reverse order it came out and plug in the harness. Before you start the car, turn the key on for a few seconds to let it prime the lines, then key off and start it up. It’ll make some noise and might be rough for a second or two while the air is relieved.
Fuel pump used:
Walbro GSS342-400-791 With Install Kit Fuel Pumps
Another fuel pump: (Might not need the amount of modification as the Walbro fuel pump needs)
DeatschWerks 265 LPH Compact In-Tank Fuel Pump w/ 08-12 WRX/STi / 05-09 LGT / 04-06 GTO Set Up Kit