NoPistons -Mazda Rx7 & Rx8 Rotary Forum

Quote:

Originally Posted by roadkill669' date='Sep 18 2003, 02:15 AM

Great post so far. It has answered many of my questions. I am in need of a new fuel pump since the factory likes to lean me out before 15 psi https://www.nopistons.com/forums/pub...O_DIR#>/11.gif .

So Camel, are you saying that if you bypass the ECU's ground to the pump and instead ground the pump to the chasiss, you can trick the pump in to pumping more fuel or just full pumping all the time??

I've seen those little fuel pump rewire kits, do they just replace the ground wire then or what??

This is a common trick in Japan, but I would not reccemend doing this unless you have a fuel pressure regualtor. Essentially the pumps rating is at a specific output, lets say 255 liters per hour @ 45 psi 13.7v DC . Now the average charging system is normally 13.7 v DC when output is not being eaten by fans, headlights etc.

Most manufactuers know you will not need to have all that pressure on a stock motor @ idle. So a variable ground system is incorporated into the ECU and output of the fuel pump is changed according to load. This is fine for a stock motor and fuel system, but when you add larger injectors you run the risk of a lean condition in the few seconds it takes the pump to go from a low output to a full output. Think of it this way, the popular upgrade to a TII or FD is to put 1000cc or 1600cc in the secondaries. If you go full throttle and the fuel pump is in low output, how fast are the injectors going to dump fuel in comparison to the pump trying to get to full output? I will try to get everything in order on wiring schematics and voltages so I have a more educated answer on doing a full output in comparison to the stock ECU output to the fuel pump soon. But I have seen the proof in a few of the cars here. One being a Nissan Skyline R31 w/ RB26 swap T-88 Turbo, 280 cams, 2.7 bore up and many other performance mods. The car had 720cc injectors installed and was litterally going lean on the top end because the ECU could not get the pumps up to full output fast enough. The car had twin GT-R fuel pumps feeding a single line. The owner of the car used the ECU's pump 12v + feed wire output from the ECU to turn a Bosch relay on to power the pumps and grounded the pumps to the chassis of the car and has not had a problem since. I am still trying to decide which fuel pump(s) I will run, I am looking at 2 options, one is twin Walbro in tank pumps similar to the Skyline listed above and the Blue FC here in Okinawa, the other is to remove the stock fuel tank and have a deep sump welded to the bottom of the stock tank and run a single Aeromotive A1000 under the car w/ new fuel lines to the engine bay in either case. Since this will be a weekend drag racer, and a daily driver through the week I am trying to keep as much hatch space as possible by keeping the stock fuel tank and not going to a fuel cell