This is a brief fitting guide to fit an unrated fuel pump into a GTI-R. Of course most cars are similar and with some common sense this guide will be helpful on all makes and models. The fuel pump in this guide is the Walbro model GSS341. The 315 and 341 flow flow similar amounts of fuel up to about 55 psi line pressure. A change in the relief valve design of the 341 permits better flow than the 315 at higher pressures. The reason for this is that relief valves often allow some amount of fuel to pass below the cracking pressure. The 341 model uses a relief valve that seeps less fuel at pressures above 60 psi than the 315 model's relief valve. At the supplied 12 volts it will flow 255ltrs an hour.
Before you start it is a good idea to have as little fuel in the car as possible. This not only makes it easier as you will be placing you hand inside the fuel tank into the fuel, but makes it a lot safer!
First off depressurise the fuel system. To do this find the fuel pump relay/fuse on the left hand side of the engine bay. It is clearly labelled fuel pump! Pull this out and now start the car it should run for a few seconds then die. Keep cranking it over for a few seconds to get rid of an excess fuel in the system. For safety it is best to disconnect the battery at this point.
Now locate the fuel pump cover under the far side boot carpet. Undo the 5 bolts holding the cover down to reveal the top of the fuel pump.
Now the cover has been removed you will have to disconnect three connectors to be able to move the cover completely away. To do this just push the locking button in on the side of the connector and pull them apart.
Once you have removed all three connectors you can slide them out of the hole of the metal cover, to do this you will have to pull the rubber grommet from out of the cover. This has now made the top of the pump visible.
You will now have to remove the large pipe going over the top of the fuel pump by releasing the clamp at the end and pulling the pipe off. There shouldn’t be much/any fuel in this pipeas it's a breather, but have a towel ready just in case.
Once the fuel filler pipe is removed you will have to remove the three fuel pipes from the top of the pump. The one that is likely to spill the most fuel is the right hand side pipe with the screw clamp. This is the pressurised fuel pipe going to the fuel rail, without depressurising the car first a lot of fuel may come out of this pipe when you pull it off.
The other two pipes are the fuel return pipe and to the charcoal canister, so not much/any fuel will come out of these. To undo the pipes just use a pair of pliers to grip the clamp together and slide it off. These pipes may extremely tight still try wrapping a cloth around the pipe and use a pair of pliers to twist the pipe side to side whilst pulling it off.
It may be a good idea to block the fuel pipe that was on the right hand side as fuel will be leaking out of this. To do this just get something the same bore as the pipe like a bolt or screw driver and wedge it down the pipe. Then tighten the clamp.
Now the pipes are removed you will see a black ring around the top of the white casing. This black ring turns turns anti-clockwise to undo. To turn this you may need to put a screw driver on the edge of one of the teeth and lightly hit it until it turns. Undo this all the way until the black ring comes completely off.
Once the black ring has been removed you’re just left with the top of the casing. To remove this you just have to pull on it, being careful not to pull too hard as there are connectors on the underside of this.
Once this is taken out, the inside of the fuel tank is now visible and you’re ready to disconnect it from the pump. To do this, disconnect the fuel pipe and the two connectors that are on the bottom of this housing. Unfortunately you will get covered in fuel from this point onwards and will be regretting doing it if you have a full tank.
Now the pipes are removed you can move the white housing out of the way and get on with removing the pump.
The pump slides on this track so removing and installing it couldn’t be easier. Simply grab the fuel pump and pull it toward the back of the car, it should slide out fairly easily.
It is now time to assemble the new pump kit. Of course kits may vary but the main goal is the same, to fit the pump in the plastic carrier. In this kit there is a foam sleaving, this is because the fuel pump is actually smaller than the original. So slide the fuel pump into the foam sleaving.
Now the pump is in the sleaving we need to use some parts from the old pump. You will have to remove the pump from the plastic casing which just slides apart. Then remove the two rubber pieces on each end of the pump. You will have to fit these over the foam on your new pump. It may be easier to slide the rubber pieces over the foam before you slide the pump into the foam. Make sure you have the correct rubber piece on the right end!
Place the new fuel pump in the carrier and align it so that the hole where the pickup clips onto is in the correct position. This is vital otherwise the pickup may not be in the best position and can cause problems when running on a low tank. Some people have reported surging problems with these pumps fitted. After testing we had no problems when running on a low tank whilst accelerating, this is due to correct positioning of the pickup. If you still experience problems, see the hot to make a surge tank guide as the use of a surge tank may further reduce fuel surging under hard acceleration/cornering.
Just slide the top of the casing back onto the fuel pump and make sure it is secure. Again check the position of the fuel pickup.
Cut the connector off of the fuel pump as near to the fuel pump as possible, as we need to use this connector.
Get the connector you have just cut off and the connector that came in the kit and crimp them together. You may want to trim the length down as the length only needs to be about 30cm. Check the polarity is correct; the GTI-R in this case had a red line on the wire of the connector that was cut off. If you want to be extra sure it is crimped correctly, you can always use a test metre to test the continuity.
Connect the fuel pipe from the old fuel pump to the new one and connect the new connector you have just made on the fuel pump. You will also have to connect the pickup at this point.
You have now finished assembling the new pump, make sure everything is connected properly and the pickup is at the correct angle. Place the fuel pump back in the tank and just follow the instructions in reverse to assemble your tank. Double check all pipes are tight and then place the fuse back and your ready to roll.
Below is a Walbro fuel pump test. As you can see from the red line, showing the GSS341 the pump performs significantly better at 13.5 volts compared to the standard 12v. Changing the supply voltage to the pump increases the flow to 265ltrs an hour and improves fuel flow at high pressure.