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Walbro 255lph Fuel Pump Install

Although the stock Evolution fuel pump will suffice for most "bolt on" mods, at some point in your modification path, you will want to upgrade the fuel pump to make sure that you never run out of fuel to supply to the cylinders. Note that fuel supply is NOT fuel delivered to the cylinders, but fuel available to be delivered to the cylinders. If your setup requires more fuel for a knock-free tune than your pump can supply, no amount of fuel tuning is going to help you and unless you turn down the boost, you could be on your way to a big problem. As always the best practice, we recommend upgrading fuel pumps before you "need" it. The Walbro 255lph fuel pump is the choice of many and we've used them for years. They are quiet (even more so in Evos), supply enough volume of fuel for nearly 500 wheel HP with the correct injectors/tuning, but are reliable enough for daily drivers. For a little over $100 and 30 minutes of your time, it is quick and cheap insurance against catastrophic lean conditions. At what point should you replace your stock pump? Like we said, it's always best to err on the side of rich and make sure fuel volume available for use is more than you need. The stock pump is fine for bolt-on mods (air filter, exhaust, etc.) and increased boost, but when you begin really opening up the air flow with cams, even higher boost, or are closing in on the 325+ wheel HP mark and are looking for more, we really think that warrants the upgrade. A few tidbits about the Evo fuel pump/tank: * There are TWO fuel level senders, one for each side of the saddle-type fuel tank. * The fuel pump gets fuel itself directly from its side of the tank, as well as the opposite chamber via a "suction hose". * The fuel pump is relay powered directly from the battery. Modded DSM owners probably know why this is important and is not a mod that needs to be done on the Evo (yeah!) If you have no idea of the implication of how indirect power supply and the resulting voltage drop effect fuel pump output, you should do a web search, but here's a hint: 15%-20% flow change between 12V and 14V! * The fuel pump operates in 2 modes: high and low. Depending on engine state and fuel consumption requirements (all determined by the ECU), the pump either gets full voltage (13.5-14.4V obviously) for added flow, or lower voltage to reduce flow, reduce pump noise, and reduce fuel vapor discharge. The high/low power path to the fuel pump either goes through the mysterious "Fuel Pump Relay 3" (full voltage) or through the "Fuel Pump Resistor" (low voltage). * Tank capacity: 14 gallons The combination of the low voltage at off-load engine states and the fuel pump being fully surrounded by the assembly makes the Walbro DEAD SILENT in the Evo! All things that make the stock fuel pump decent, make the Walbro even more amazing than it already is.

1. Do not do this on a full tank of gas. On Empty would be good...the less in the tank, the less chance of spills. Don't be foolish or lazy when you are working in close proximity to open gasoline...no open flames, sparks, etc...and a fire extinguisher within reach is always a good safety measure!
2. Remove the bottom of the rear seat by using these tabs on both sides to release it from the catches. There is one tab under each side of the seat where the seat bottom meets the foot well. Detach the seat bottom by pulling the tab towards the front of the car. Remove the seat and set it in a clean location.
3. Remove the fuel pump assembly cover from the driver's side of the rear seat by removing the (4) Phillips screws holding it in place. There is a similar cover on the passenger side with an assembly that houses other fuel related sensors.
4. OK, now before going any further, you will want to release the pressure on the fuel lines by removing the "Fuel Pump Module Connector", or in non-Mitsu terms, disconnect the harness (circled in the pic). After the harness is disconnected, start the car. It should either not start at all or start and then quickly die. When the car no longer runs, turn it off and remove the keys from the ignition just for added security.
5. Now a quick rundown of what each connection is you are looking at before you rip everything apart: - High Pressure Hose: basically the "out" of the fuel pump, ultimately connecting the tank to the fuel rail supply side. - Suction Hose: connects to the assembly on the opposite side of the tank (under the cover on the passenger side) to pick up fuel from there. - Return Hose: returns fuel that the fuel pressure regulator by-passes back to the tank. - Wire Harness: er, powers your fuel pump, among other things.
6. Your wire harness should already be disconnected from Step 4. The high pressure and suction hose both use quick disconnects. Remove them by simply squeezing the tabs and pulling them off. A spring clamp holds the return line in place, so grab your needle nose pliers, squeeze it together and push it back up the hose. TECH TIP: "breaking" the return line loose by spinning it before trying to pull it off the barb may make your life easier. Additionally, keep in mind that the pump module housing is plastic and can crack if you twist, bend, bang, push, or pull too hard.
7. The (6) 8mm retaining bolts need to be removed. Removing the rearward 8mm bolts is most easily accomplished with an extension on the ratchet or a nut driver, but you will need to get under the sheet metal to reach the front ones. You can try an open end wrench (best of luck to you!), but a nice short 8mm socket on a 1/4" drive is really what is required on them.
8. Once all the connections and (6) 8mm bolts have been removed, you will need to "finagle" the assembly out of the tank. There is little room to move and the retaining ring on top makes it even more difficult since it is physically wider than the opening in the sheet metal. The real kicker is that the suction and return hose barbs stick out way over the top of the ring making it a chore to try to get the ring off first and then pull the housing. We can't really offer any tips on getting it out, but you will need to lift up and angle the whole shebang to get the retaining ring out and then pull the pump assembly straight out once the ring is removed. Be careful not to manhandle the fuel pump assembly when moving it around to get the retaining ring off. As you will see in the pictures, the fuel level sending unit arm/float are connected to it (sticks out the high pressure hose side) and too much force may bend it, which can throw off your fuel gauge reading. Just make a note of it. Also be careful not to drop the gasket from the assembly into the open tank as/after you pull the entire assembly out.
9. When you remove the assembly, there is likely to be fuel in it since it has a reservoir of sorts. There may also still be some fuel in the pump as well, so when you remove the assembly and during the process of removing the pump from the assembly, make sure that you have something to absorb any spilled gas, like our kick ass shop towels seen in the picture! In all seriousness, paper towels may actually be of better use here since they will dry quicker than cloth rags and you won't want to leave rags with dried gasoline in them laying around....you can just toss out the paper towels after they dry. TECH TIP: when you lay the assembly down to work on it, make sure the fuel level sending unit is in the air. Do not lay the pump assembly with the float/arm down and be careful not to hit or bend it while you are working.
10. The fuel pump retainer simply snaps to the main assembly using (3) tabs. Removing the retainer is simple, either by hand or using a flat head screwdriver to pull the tabs away from the main assembly and sliding it down. Note to step 11
11. The bottom pic is the retainer removed from the assembly. You can see all three tabs on it and the rubber isolator.
12. With the retainer removed, simply pull the pump out of the housing. The wire harness plugged into the top of the pump only extends to the bottom of the assembly, so do not try to pull the pump all the way out. Pull it down and unplug the harness from the top.
13. With the pump removed, you can see the harness and the factory "o-ring" (grommet) still stuck in the outlet. The factory grommet is more like a hat than an o-ring in that it covers the top, as well as a good length of the outlet fitting (see insets). As soon as we saw how "manly" the factory grommet and spacer were, we decide that the o-ring and cap setup provided in the Walbro install kit just looked "dainty" by comparison, so we re-used the OEM outlet setup on the Walbro pump.
14. Digging in to the Walbro install kit, grab the new pump filter and the small retaining ring and install the filter onto the Walbro pump. Set the filter in place and push the retaining ring on as best as you can (just so the ring doesn't fall off). Place a 5.5mm or equivalent socket over the retaining ring and gently tap it on until it sits flat against the filter housing.
15. Install either the Walbro o-ring/cap or OEM grommet/spacer onto the pump outlet. Here, we have re-used the OEM setup. The factory harness plugs right into the Walbro 255lph and it's almost ready to be slid back into the assembly. Whether you re-use the OEM grommet/spacer or the Walbro o-ring/cap, the outside of the grommet or o-ring should be lubed with a light oil so it slides easily and seats properly in the housing. Note to step 16
16. OK, now slide the pump in. Be careful that wires don't bunch up anywhere "awkward" as you slide the pump in. When the pump outlet nears the top, look through the side of the assembly to line up the outlet with its home in the top of the assembly (bottom pic).
17. With the Walbro fully seated in the assembly (top/left), grab the rubber isolator included in the install kit and lay it on the bottom of the pump (top/right). Note to step 18
18. Snap the retaining cap onto the assembly over the isolator and you are all set to reinstall the pump back into the tank!
19. If you removed the gasket from around the top of the assembly, reinstall now as seen in the picture.
20. Do you remember how you got the pump assembly out of the tank?? Good, because now you need to get that sucker back in there! Spinning the assembly so that the suction hose fitting passes through the corner (bottom/left corner in our pic, front/left corner on the car) will offer a little more room to move, but it is still a tight fit. It may be easiest to get the retaining ring under the suction and return hose fittings before trying to get both back in/on the tank. Also note that the retaining ring is keyed to (3) tabs on the pump assembly, so it will only fit properly in one orientation. It's a good idea to get the ring in position before you try to reinstall. Er, make sure that the assembly itself is in the correct orientation too! The fuel level arm and float should be facing the passenger side of the car.
21. Once the pump assembly and retaining ring are properly seated, tighten the (6) 8mm nuts in a criss-cross pattern. Torque each nut to 23 in/lbs. Tighten the bolts before you reconnect the hoses and wire harness. This will keep the assembly from moving around while you push the hoses on. The suction and high pressure hoses simply snap back on their quick connect fittings, but the return hose will require some pushing to get back on. Don't forget about the spring clamp that you slid up the hose! TECH TIP: a little bit WD-40 or other light lubricant around the return hose barb fitting will let is slide back on easier.
22. After everything is properly connected, give the car a start to make sure it's getting fuel. Don't be scared if it takes a few cranks before it fires over. Remember, you ran all of the fuel out the line and it needs to fill back up and pressurize again. If the car starts and everything is wonderful, replace the steel cover over the pump assembly and then replace the seat...it simply tucks under the seat backs and then snaps back into the clips. Don't forget to pull your seat belts over the seat bottom! Now that wasn't so bad, was it?
23. Unless you were running lean before the install due to more demand than supply, you will likely want to retune your fuel adjustments down just a tad, but there is no problem without any fuel control at all...you'll just be a little rich. With the added flow of the high-volume fuel pump, base fuel pressure has a tendency to increase 5-10psi, which will run you a tad fatter across the board. This added rail pressure may be a "side effect" of the high-flow pump, but by allowing you to lower fuel settings across the board, it has also just increased your margin of "fun" before you hit fuel cut!

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