Last job is to reconnect the battery, turn the ignition on listening for the fuel pump to prime itself, and start the car up! Easy! You now have a pump delivering more fuel, at a higher pressure if need be, giving you less chance of the car running lean and potentially causing engine damage. When i had finished insulating the new soldered connection i bound all the three new wires together in a nylon wrap for even better mechanical potection and replaced the cover. Imagine my surprise when i found this simple connection gained me another 0.5 volt ! A well worth while modification in itself! As an experiment i thought i would also try uprating this connection using a thicker gauge wire here too, piggy backing it onto the oem negative cable and simply fastening it down to the chassis at the nearest point. One connection that no-one ever seem's to mention is the negative connection off the fuel pump. This method is relatively easy on the Evo 7/8/9, it is slightly harder on the Evo 4/5/6 given the limited access but the wiring method is the same.
A way to increase the voltage at the pump is to take a feed straight from the battery, via a relay, run in a thicker cable, and thus giving you less resistance = more voltage. Although you may not realise it, you lose around 2 volts between the battery and the pump, this is known as 'voltsdrop' and is caused by the resistance in the oem wiring. Hardwiring the fuel pump is a good method to ensure you get the maximum output from the standard 'intank' fuel pump, be it the oem mitsubishi one or the most commonly used aftermarket pump, the Walbro GS342.
#Evom fuel pump prime how to
If you do not know how to connect such an easy thing as a relay you should really consider asking yourself if you should be taking on any wiring modifications in the first place. So with the relay's supply in and out sorted with the thick orange wire, all that is needed is to connect the purple trigger wire, and then a short negative wire from the relay to the battery's negative terminal. In this photograph you can see that i have actually soldered another wire to it, this is for a second fuel pump (a Bosche 044), which i run in-line with the Walbro in tank pump. The wiring on the right is the new thick supply wire that runs to the fuel pump. This needs to be fused as you can see on the peice of wiring on the left of the photo. You need a small relay, i used a 40amp one, and to that you need to connect the main supply off the battery. In the engine bay things are relatively as easy. Modifying the cover is easy, simply place the edge where the wires run on top of something round, say a 10mm socket, and hit either side with a hammer so as just to give enough room so you dont squash the cables when the cover is put back into place. It has also been suggested that you can use insulated crimp connectors in place of soldered joints if you are not confident in soldering - this also means you'll have no nasty burns in your carpet should the unfortunate happen! As you can see i have also taped the two wires together, and added a few layers to the metal work were they run, to help protect them against chaffing.
Once you have soldered the wires in place, make sure you insulate the connections well using either heat shrink, or if you dont have any available, Electricians tape like i have done. The feed into the pump's top plug needs the new thick supply wire soldering to it, and the original feed needs the thinner relay wire soldering to it.
The thicker the supply wire the better, as you will lose less volts, however you need to offset this against how easy it is going to be to run the new wiring in place.Īfter you have ran in two new wires from the engine bay to the inspection hatch, the wire you need to cut is the main red oem feed to the pump. The wire i would recommend to use is 1mm for the relay tigger wire, and either 2.5mm or 4mm wire for the new supply. As always when working on the electrics, before you do anything, disconnect the battery!Īccess to the pump is via the inspection hatch under the rear seat.
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