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New Fuel Pump, Used WRX

An easy job involving few explosions

Lots of folks fear swapping the fuel pump on injected cars. First thing they see when looking at the manual, or inspecting the setup, is that the pump is in the fuel tank—immersed. This is done because the gas in the tank helps cool and lubricate the pump's moving parts, and to compartmentalize the unit for easy assembly at the plant. There are likely a few other reasons too, but we haven't thought of those yet. No matter, the point to be made is that doing the fuel pump is easy. Just take a few precautions.

Address the Fuel Pump

The primary hitch is tank location. On some vehicles, you have to remove the fuel tank to access the fuel pump—5.0 Mustangs, for example. Not difficult, but not quick. On the Subaru Impreza WRX, the pump lives under the starboard service port in the trunk, hidden only by the trunk's liner. The Japanese always design smart stuff like that. The reach is a little hard on your back, but be grateful it's just that.

The WRX fuel pump is what you would call a weak link. With OEM designs come compromises, and the little pump that shouldn't was installed on every WRX through the 2005 models. At peak boost levels (even stock), the unhappy little thing is maxed out, and on a cold, fast day, they've been known to let the engine go lean. If you've made any engine modifications to your turbo'd Sube, you need a bigger fuel pump. Even if you've left your Subaru stock, it wouldn't hurt if you like to explore higher RPM zone. Don't think that a new pump will send you all rich and slow, either—that's what the fuel pressure regulator is for. It minds how much gas actually makes it to the motor. Ramping up pressure just means that more fuel is available when you require it.

Sink Your Teeth into the Tank

Official words of caution: Gas isn't easy on stupidity. The vapors are more flammable than the liquid fuel, so you usually don't need to be stupid up close, just nearby. No sparks, no tool-to-tool banging. If you're working in the garage, keep the big door WAY open to help vapors disperse. Cover the open tank while you work. If you don't have a fire extinguisher in the garage, this exercise is a good excuse to get one. Also, please disco the battery on the car and ground out the terminal to the chassis so there's no leftover juice stored up in the stereo or ignition.

With the nuts, bolts and the access cover removed, you wind up looking at a plug, a few hoses and the pump cap on the tank itself. It's sealed, but easily pries off. Mind the seal (you'll want to preserve that), and note the location of the locator ring that ties into the actual pump housing/cover plate. Unplug the pump. The fuel lines pop off readily after you've loosened the hose clamps, but don't be afraid to use a little leverage when you coax the hoses off. Prying the hoses off requires a bit of force, you understand. If you don't damage them, you won't have to replace them. It's best to have a rag shoved into the gap to catch errant fuel, because there will be drips. One of the hoses is connected with a fast clip, and all you need to get that off is a well-aimed set of needle-nose pliers (the greatest tool since the hammer), and no force. DO NOT damage this clip unless you planned to buy new fuel lines at your Subaru dealership anyway (it's incorporated into the line).

The fuel pump is a part of a larger assembly in the tank that also contains the fuel-level float, so be gentle, patient and cautious in removing it or you'll bend the float arm. It WILL all come out in one piece, so don't doubt initial difficulty. Fuel will drip from the assembly, so more rags aren't a bad idea to have around. This job has a high-rag percentage.

Minor Details of the Pump Swap

Avail yourself of a sensible space to work and get busy exorcising the old pump. It's only a matter of a few hose clamps and a snug fit. You'll probably have to trim the supplied new hose to match the old unit's length. Don't try to reuse parts if a replacement is supplied new with your upgraded pump kit, because the gas in a fuel tank is pretty hard on rubber parts. A rubber foot, which secures the pump into the assembly and also dampens vibration, will come out when the original pump is removed, and that's disposable (as long as your new pump has one in the kit like it's supposed to).

We mentioned the EFI 5.0 Mustang fuel pump earlier. Coincidentally, the pump we're installing on the WRX is the same Walbro unit as is used by lots of Mustang tuners on mildly modified injected 'Stangs (as well as dozens of other hi-po applications). The pump itself is only one component of the total fuel assembly, so it can be used/exchanged according to fuel needs as well as fitment.

Don't overcomplicate this thing: Swap the pump and close up the tank and you're done. Be sure to mind the danger of fuel fumes while you work, keeping doors and windows open to circulate all the air you can. Other than the weird maneuver of removing and replacing the entire fuel pump housing, this is a cake project.