When the car getting old, the wiring in the engine are being oxidize and the voltage will drop from time to time. Another factor that will cause this drop of voltage is the heat. This is quite obvious for the turbocharge engine because it produce a lot of heat in the engine bay.
Before i decide to pull a direct power from battery to my fuel pump, i did some checking on the voltage that supply to my fuel pump. The BPT/GTX is equiped with a 2 stages relay+resistor for the fuel pump. It will suppply low voltage when the ignition key at ON and ~12v after the engine start. On the stock setup, my fuel pump was getting ~11v after engine is start. This is somehow a bit low from the manual. The worst case is when i pull out the wire on the stock relay+resistor, the fuel pump is still working, by right it should be no more power to it. This mean that during the conversion, the mech was not using the power from the stock relay+resistor and simply get from other source.
Parts that needed for this work:
1. wires 5-6meter depending to ur wire route
2. automotive relay (i get bosch 0332-019-150) any 30A relay is working fine
3. 30A fius
4. sumitube
5. crimb
The idea on this is let the fuel pump get a direct power from the battery, meaning it will get ~13v all the time. And for safely purpose, the fuel pump should stop and the key turn to off. For this to work, this is why we need a relay. The trigger for the relay to allow the power from the battery to fuel pump will be the existing powersource to the fuel pump. The wire diagram i get from Jeff Lucius at
http://www.stealth316.com/2-fuelpump-rewire.htm Anyone own a Stealth 316 should refer this site. It provide a lot of information.
First is to do the terminal connect to the battery and also the crimb to that hold the fuse. I use sumitube to cover the join to avoid it to expose dust, water...etc
I pull this wire under the carpet and go to the rear seat. This wire is connecting to the battery +terminal and 30A fius. It later going to connect to the pin 87 on the relay.
Next is to identify the wire that power the fuel pump. Normally there are few wires there for the fuel pump and fuel level gauge. Please refer to ur car wiring manual to identify it. Another way to do this if u do not have the wiring diagram is take out the fuel pump and identify which wires it connect to the pump :) But be careful when removing the fuel hose.
After identify it, cut the wire and connect a crimb on it. Make sure it long enough to the relay else wire extention will be needed like my case.
The wire that being cut into 2 will be then connect to the relay as well. For the one go into the fuel pump, it will connect to pin 30 and the other one will be connect to pin 86. For the ground, it can connect to body of the car and pin 85.
Once all connections is plug in, is time to check the relay is working fine. If u have a voltmeter, u can check the voltage on the cable that connect on the pin87, you will always get the same reading on the battery ~11v before car start and ~13 after car start. Other pin should be always 0v before u tun the key to ON.
To make sure the relay is wokring, turn ur key to ON and you should hear the fuel pump is running. Turn the key to OFF and the fuel pump should stop as well :) Now start your car and you can measure the voltage, u will get constantly ~12-13v to the fuel pump. Next is to use the black tape to cover the connection on the pin. This is to avoid the wires being accidentaly pull off. Now u can take ur car out for few run, then check the wires and also the relay. It should not run too hot.
Pros:
1. Fuel pump getting higher voltage thus provide higher flow.
2. Cheaper solotion compare to replace the stock relay+resistor. Sometime this spare might not even exist in the local spare part shop due to the car is not sold locally or lower demand or end of sales.
Cons:
The lifespan of the fuel pump might reduce due to it work hard all the time. But this is very subjective topic because some newer car model also does not come with 2 stages fuelpump relay.
