If you are running more than 12psi of boost, you should really upgrade your fuel pump. The standard fuel pump will start struggling to deliver enough fuel above this and that means your could start running lean at higher revs. Running lean means Det and bye-bye engine. Even if you simply need to replace the fuel pump, replace it with an uprated pump, as it will undoubtably be cheaper than the Nissan replacement.
The popular choice is a Walbro GS-341 (also known as a 255 due to it being capably of pumping 255 litres of fuel per hour). This guide shows how to fit one of these.
You will need a blunt flathead and crosshead screwdriver, a mallet, pliers, a pair of wire crimps and a couple of old cloths. It is advisable to have a few pairs of rubber gloves too, unless you enjoy the smell of petrol on your hands for a day or so.
It is best to do this job when you have less than a quarter of a tank left.
Firstly: open all doors and the boot to get as much ventilation as possible. Next, start the engine and pull the fuel pump fuse. Its the third down on the right in the footwell fusebox (15 amp). The engine will stop fairly quickly. The reason for this is to clear the fuel line and release pressure. If you don't, petrol will piss everywhere when you disconnect the hoses.
DISCONNECT THE BATTERY. Next, disconnect the battery if you just ignored that! One stray spark from a live electrical connection and you won't be around to worry about not doing it.
Drop the rear seat back. You will see a gray cover over the bulkhead. Remove the two black lugs holding it in place and fold it back into the boot. You will now clearly see the plate covering the fuel tank (Figure 1).
Use a crosshead screwdriver to undo the four retaining bolts. They are quite easy to undo. Lifting the plate, you will see that the cables feeding through it are connected (Figure 2). Unclip these connectors and swivel the plate back out of the way. The connectors are two and three pin, so they will only re-connect correctly.
I marked up all three fuel hoses to identify them easily when reconnecting later. Undo the screws on the two left hose grips and move them back along the hoses. Use pliers to pinch the right grip back.
Appended for S15
Figure 3a shows the fuel pipe connections for the S15. As can be seen, they are considerably simpler to remove and replace. Be warned, however. Fuel is much more likely to piss out everywhere when you remove them. Ensure you have a great deal of cloth ready to catch it.
Carefully remove the hoses from their connections. Make sure you have a cloth under each one, as there will still be some excess petrol in the hoses, especially the left ones. Move the hoses back out of the way to allow unrestricted access to the fuel tank lid.
There is a screwable black cap holding the white centre lid in place (see Figure 3). This cap will be very tight and will probably need removing (and replacing) by tapping a blunt flathead screwdriver on the ridges. Don't tap too hard or the ridges will be damaged.
Put on your rubber gloves now. The white lid will pull out from the tank. You will see two fuel pump connections attached to the cap (Figure 5). Disconnect them and place the cap somewhere were it won't get dirty. Disconnect the fuel hose from the cap.
It is quite difficult to explain how the pump holder is mounted in the tank. I was unwilling to risk being blown sky high by taking a flash photo near/in the tank but, helpfully, SXOC Board member 'Bob's S14' wasn't! You can see in Figure 6 that the holder slides over a clip attached the diagonal front edge of the fuel tank (behind the rear seats). Figure 7 below may help you a bit more.
Have another cloth ready here. From the boot side of the tank lid, put your hand into the tank, grip the holder and carefully lift it up and towards you. As you remove the holder and pump from the tank, you will see the filter attached to the bottom of the pump. Place the cloth under the filter to avoid dripping petrol everywhere.
Lie the pump in a relatively clean work area and take a look at it (Figure 8). The pump itself isn't actually fixed on by anything except the small length of hose on the left. Using pliers, release the pinch grips on the hose. The pump should pull out of the hose. It can then be twisted out of it mount on the right.
The fuel filter that comes with the Walbro is pathetic to say the least. I would recommend that you either transfer your existing filter or get a 300ZX item. If transferring, Turn the pump with the filter pointing up (Figure 9). Be prepared for petrol to come out! Carefully remove the tiny circlip holding the plastic adapter on and take it off.
Turn the pump over. You will see the electrical connectors (Figure 10). The connectors are not required for the Walbro so cut both wires, leaving about 15cm of wire on the old unit. This is in case you need to refit or sell it.
Appended for S15
Figure 10a shows a comparison of the S15 fuel pump with the Walbro. As can be seen, they are VERY similar, right down to the electrical connector. There is no need to alter the existing wiring at all. The existing connector will simply plug into the Walbro (as shown). They are so similar that I even suspect they are the same model.
Unpack your Walbro! Attach your filter onto the bottom and secure with the old circlip. Make a note of how the new rubber washer seats (Figure 11).
Cut the piece of hose supplied with the fitting kit down by about 3cm. Attach the new hose to the holder and pump and seat the pump and washer in the holder end. The hose needs to only be sufficiently long enough to ensure that the pump and rubber washer sit snugly and firmly in the end of the holder.
Using wire crimps, splice the new connector wires to the old using the two crimps supplied. If you are in any doubt, its red to red and white to black. It is not sufficient to twist the wires together and stick some insulating tape on. The petrol vapour of the tank will make the tape come off in no time, the wires will spark and you'll suddenly have a terminal amount of boost. The wires should not be exposed at all. The safest solution is to solder and shrink wrap them. Once done, plug the new connector into the Walbro.
Appended for S15
Due to the fuel pump holder being made to hold a pump the same size as a Walbro, you would expect the Walbro to just fit straight on. In reality, I found it quite fiddly. You may have to adjust the pipe length, you may not. Try the fitting before altering anything. One other important thing to note is that the rubber washer supplied with my Walbro did not fit the pump holder. I had to use the original.
As an added precaution, I zip tied a length of rubber hose around the lower half of the pump and holder. I did this to ensure that the holder didn't rattle against the side of the tank when refitted. This isn't essential, but I'd have been well pissed off if it rattled after I'd put it all back together!
The pump and holder can now be carefully slid back into the fuel tank and back onto its bracket. ensure that it is held firmly.
Reattach the pump's electrical connectors and fuel hose to the white lid. Tuck the wires back into the upper end of the tank and replace the lid in the same way it came off (see Figure 4).
Screw the black cap back into place.
Slide the top plate back into position and screw the bolts back. Secure the cloth cover into place and put the rear seat back up.
Put the fuel pump fuse back in.
Reconnect the battery.
Start the engine and let it tick over for a while to ensure everything is back to normal, then go and enjoy your new fuelling!