mad_7tist

of course increasing the pump volume ,via increased voltage, may require a retune of a car that was tuned for a lower voltage.

12v = 40psi(a volume limited figure) = %50 duty cycle( to run "correctly") = x amount of fuel

14.2v = 48psi(what the regulator was shooting for) = same duty cycle as before = to much fuel

your car is going to need x-amount of fuel to run period. if the pressure is lower it will need larger injector on time if it is higher it will need less time, but the amount of fuel will be the same.
(disregarding any benefits that arise from the higher pressure/atomiztion patters)

the speed system keeps the pump quieter when at idle etc and should prolong it's life, it is not for fuel economy per say.

GoodfellaFD3S

iTrader: (213)

My esteemed colleague Dr. Huk was nice enough to perform this mod on my FD recently to prep my R1 for an impending dyno day. The pump now sees 13.5 to 14.0 volts at idle, it pretty much mirrors what my PFC is telling me for battery voltage.

I don't have enough seat time, but I can tell ya the Apexi BNR fuel pump BUZZES pretty damn loudly at idle---you can even hear it over the 4 inch open exhaust. Just one step closer to sounding like a race car I guess

As an aside, I have run as high as 20 psi on the street with the stock fuel pump wiring. Fuel pressure never really seemed to mirror what it should, ie base fuel px 40 psi, peak of only 58ish psi.

Julian

iTrader: (14)

Most of the gain in voltage drop comes from bypassing the ignition switch and extra grounding at pump; smaller gains (i.e. diminishing returns and greater tradeoffs) come from running new wire from front to back; and from bypassing resistor relay. To me the resistor bypass is not worth it and the wire rerun front to back is marginal (at most, I would just parallel a new wire from convenient junction at footwell back to pump connector above tank., definitely no need to carry new wiring down into tank. Electrical resistance is like water flow resistance is the sum of all restrictions, a few don’t hurt much a lot do, removing the first big obstacle gets you to most bang, the last restriction remove may not even be noticed. That is the OEM wiring is NOT undersized for the amperage. Has anybody done the Ign switch bypass and then measured voltage with and without resistor relay bypass.

TitaniumCranium

iTrader: (3)

I assume then that if you are running a non-tunable ecu that this mod should not be done, or am I wrong. I am currently using a pettit unlimited ecu so I am not sure if I would just end up running way too rich, then what would be the point. On the other hand maybe the maps are based on 13.5 volts to the pump above idle. I dont have a wideband so I have no way of monitoring a/f. What to do...

David Hayes

iTrader: (6)

Okay, I am confused so help me out here. My car is modded (I think) just like the wiring diagram in this thread. The problem with doing this is the fuel pumps (I have two) get full power all the time, even at idle. This means the pumps are churning away at 22 amps, even at idle. I'm assuming the gas has to be circulated somehow back into the tank, even though little fuel is required at idle. So, in solving one problem (fuel starvation) we have no created another (excessive pump use) haven't we?

What am I missing here? Does an elegant solution exist for ensuring proper voltage to the pumps while not overworking the pumps at idle or what am I missing.

Stumbled on this thread because I am tracing down a voltage issue and just couldn't believe my pumps at idle needed about 22 amps. The reason is because they run full bore all the time!

Dudemaaanownsanrx7

iTrader: (23)

I suppose someone could leave the stock wiring completely alone, except for a heavier ground. Then run a second heavier wire relayed in with a boost activated switch. This way the resistor is still retained, and idle and cruise is left alone. Under boost you have the extra voltage when you really need it. I'm not sure if a diode would need to be installed on the stock circuit to protect the resistor pack, i wouldn't think so but thats an option if necessary. I'm not sure how much extra life a pump gets at 9 volts compared to 14, i doubt its a significant difference though.

David Hayes

iTrader: (6)

anyone else care to comment?

Rexy225

Good info. I just installed a new pump in mine and I still have a crank no start problem in my rhd fd. I have built this car from scratch and am still trying to get it running. The rubbber piece on the bottom of my old pump was like completely melted and was a tar like consistency. I am still having to go back to the drawing boards...

Julian

iTrader: (14)

As to Mazda’s fuel pump supply design, I find it hard to fault them for what they did given that number one they needed to meet safety regulations and supply enough fuel with some margin to a stock engine. They did just that. A primary safety feature of a car is fuel shut off; they have roll over kills, and direct power kills, pulling direct through ignition will kill power whether the relay sticks or not. Our race cars are not much different, with both a fuel pump switch and overall electrical system kill switch accessible from outside cabin with car upside down.

Julian

iTrader: (14)

Bouncing this question off my motor design people at work (we design and manufacture AC, DC, AC-VFD, and SR motors from 15 to 3000 HP for our line of products), a factor of plus or minus 3 times the life; volts = heat, heat = insulation degradation, insulation degradation = death

Julian

iTrader: (14)

Of course Mazda had a solution with the offline resistor bank that was relayed into the circuit under idle to cut voltage, but many people wired around this in the process of setting up a direct power supply. There are some solutions keeping at least that part of the circuit intact, see some of my prior posts, bypass ign switch, back into fuel harness and then in footwell conector to rear harness double up wire .. keep orginal but link in a parallel wire and run it back to connector outside of tank (it was not bad, only the ignition pass through was the big voltage drop bottle neck) or install alternative fuel pump power supplies such as from MSD or Aeromotive:

Aeromotive Billet Fuel Pump Controller
Model: AER-16302
List: 164.56GBP

Aeromotive Billet Fuel Pump Controller

For any pump, on any type of vehicle, this voltage stepper is like an automatic transmission for your electric fuel pump.

Whether you’re just cruising or running at Wide Open Throttle (WOT), Aeromotives Billet Fuel Pump Controller senses engine RPMs, then automatically delivers the correct voltage to the Fuel Pump. An adjustable controller lets you calibrate the desired RPM level for your specific application.

Controller features:

-LED indicator confirms correct ignition signal hookup, verifies energization of the manual override circuit, and indicates that the circuit is providing full voltage to the pump.
-A solid-state transistor circuit replaces the relays recommended in most fuel pump electrical circuits.
-Cool operation mount it virtually anywhere.
-Housing crafted from billet 6061-T651 aircraft aluminum alloy, protected with a beautiful bright dip red anodized finish.
-Complete installation kit �wire, override toggle switch, installation hardware, and instructions included.


Edit Warning: After going to Aermotive web site (sorry I am in London today and my Google sent me to weird sites (not quote above in Pounds), this unit seems to be discontinued and replaced by Aeromotive 16306, carful the have a digital unit 16303 but its for returnless fuel system only, another programable unit is made by MSD and may be more appropriate for our application. I have not purchased or installed any fuel controller and am not endoring any make or model they just seem like a cool solution.

Julian

iTrader: (14)

Example of wiring connection for 16306

Speed of light

iTrader: (8)

Actually it's probably going to be quite significant. The power input to the pump is going to vary as the square of delta Volts (the change in voltage) in most instances. So lets say the pump draws 15 amps at 14 volts, the power input will be 210 watts, some of which produces useful mechanical work and the balance is lost to heat. If we reduce that same pumps voltage to 9 volts, its current draw will be reduced to about 9.6 amps with a resulting power input of ~87 watts. That's a big difference....

You dual pump guys should consider doing it the way it's done in many aircraft: Run on one pump and configure the second as a booster pump. This would entail using a check valve in the line of the second pump and wiring the second pump from a boost relay or similar control so that you have full capacity at high load. There's no point in running a second pump all the time, as you're just heating the fuel, among other things.

Dudemaaanownsanrx7

iTrader: (23)

I'm running stock pumps which i've never actually heard of a failure on, not that it never happens but it's rare. It seems most pump failures are for no particular reason. I think a larger effect on pump life is how empty your tank stays. Without fuel over the pump the pump runs much hotter. Personally i rather have the increased fuel delivery from better wiring. Plus better wiring is a must with 2 pumps. If running twin pumps in steps the main pump will still run constantly so you're only extending the life of one, which could fail first just out of bad luck. The adjustable voltage thing would work well but i would prefer it boost based rather then rpm.

IRPerformance

iTrader: (41)

On some cars I only gained half a volt or so after bypassing the fuel pump resistor with a jumper wire at the relay and adding an additional ground at the pump. There is also a power wire at the circuit relay that can be run to the battery but I have had the best results in just wiring a relay at the pump.

IRPerformance

iTrader: (41)

You might be better off reverting to the stock fuel pump resistor setup and upgrade all the wiring in that circuit. Just make sure the pumps can keep up under boost.

David Hayes

iTrader: (6)

The balance I am assessing here is the amps consumed (22 amps) at idle with the pumps wired in this fashion as well as the wear and tear on the pumps having them being run "full bore" all the time versus having less amps consumed by taking off this mod and less wear and tear.

My newly ordered alt will push the amps I need so this won't be an issue but wear and tear is. I've spoken to Jesus on this and he says he can wire the pumps so one would be on all the time with the second coming on under boost. Kind of a hybrid solution if we can use a mod of the current setup.

Julian

iTrader: (14)

David, perhaps more significant that the wear and tear on the pumps is the heating fuel by both the pumping action and the excess recirculating flow through the engine compartment.

Double_J

iTrader: (28)

Without being terribly abusive can someone explain what two points you attach to see your voltage? I have removed the cover and see the connector. Is that where I should expect to see 13.5 volts?

I would like to test the volts before and after.

Dudemaaanownsanrx7

iTrader: (23)

^^ The red/white wire and black ground wire in the rear behind the fuel pump cover. See the diagram above, it's the same wires you can splice into to rewire it.

FD3S2005

iTrader: (11)

so where do you guys keep the relay at?

RotaryBuddha

iTrader: (4)

I put mine in the hatch area. Just to the left of the fuel pump cover. Underneath the carpet on the shock tower. Their is plenty of room in their.

David Hayes

iTrader: (6)

So, I might be the first casualty of rewiring like this. Pettit did this mod for me about 4 years ago during my 3 rotor conversion. As you know, my car hasn't seen much driving time since then (maybe 5,000 miles) but it looks like one of my fuel pumps has gone out. I had two new Denso fuel pumps installed, giving me 40 PSI. Went out to the car a few days ago and it is now 20 PSI. Barely starts. Took the car yesterday to Jesus at Kilo Racing in Orlando and we're about 95% certain one of the pumps has gone out.

Remember my earlier questions about pump longevity? Looks like we might now know more about this thru my experience. Based on my experience, running the pumps at full voltage can possibly cause them to wear out more quickly. Maybe just bad luck in my case or maybe not.

Also, note that if you do this, the AMP usage on your car will go up a lot. At idle, the Denso pumps run about 7.5 amps total but when at full voltage like this mod will do, they're at 22 amps.

So we are thinking now about another setup, one that uses the Microtech to control the second fuel pump. We're thinking about running one fuel pump "as is" (full voltage) and then turning the second one on during boost or according to RPMs or something like this. I know this won't entirely fix the problem of running full voltage but it is a start. I am also going to look into the AEM product posted earlier here as a potential solution also.

As for where to mount the relay, I have mine installed all the way in the left back of the car, behind the plastics that also hoes the rear tail lights.

David Hayes

iTrader: (6)

So per julian's recommendations, I looked up the Aeromotive and the MSD fuel pump controllers.

The Aeromotive unit:
http://www.jegs.com/i/Aeromotive/027/16306/10002/-1

Works according to RPMs and increases voltage to the pumps accordingly.

The MSD unit:
http://www.jegs.com/i/MSD/121/2351/10002/-1?CT=999

Works according to boost and increases voltage accordingly.

Both will set you back about $350 so they are not inexpensive.

Curiously, these were the two options we discussed by using the Microtech ECU to control the fuel pumps so I don't think I need one of the solutions above although I might as I am not sure I can completely control the pumps like the boxes do (not sure you can "step" voltage thru the Microtech).

FD3S2005

iTrader: (11)

so you have a little buldge showing from the carpet then?