Anyone here re-wired their OEM fuel pump?

I am having my PowerFC tuned by a rotary shop in New Zealand and they are sending me a 1.2 bar map they have been using for years on their FD with a stock ifuel system running 98 octane.

I asked the guy how they managed this, and he told me about wiring the fuel pump directly from the battery. He says that Mazda's engineers in an attempt to keep noise down, wired the pump very strangely, and in turn it only receives maybe 2-4v on the line. By wiring it directly with a circuit breaker and relay, the pump will recieve the full 12-13.5v and will actually be a great pump?

Has anyone here tried this?

 

nope but i am very interested

 

It sounds like they bypassed the fuel pump resistor. This will only put stress on the pump, and you will just keep pumping gas from tank to engine bay to tank at high flow. The Ecu controls the Fuel pump relay that shorts the resistor at high demand, so you normally are in bypass at high load but a low load the fuel pump can relax a bit. It shouldn't make any difference to absolute flow rates from stock pump. IMHO

 

sounds similar to what the DSM guys have been doing for years.... rewiring to eliminate the current drop . they run a seporate relay and like 12 gauge wire wich is overkill
tests show in high load withe the current not falling they get like 15% more flow

 

Or you could just be safe and spend $250 @ the RX7store for the Denso Competition pump and be good up to 500hp (20 minute or less drop in replacement install).

http://66.216.67.51/product.asp?0=211&1=260&3=320

The pump is very quiet unlike many high performance pumps which have a very annoying whine, ie you CAN NOT hear the Denso running from in or outside the car.

After my install, I shorted the pump to verify it was running and coulnd't hear it unless I did the old screwdriver to the gas tank and side of head trick.

k

 

Bypassing the resistor is common practice for people with Haltech and PFC...it also eliminates the 3k hesitation. The normal fuel system has the resistor there to draw a lower current for slower speeds, then bypasses it for more current at higher speeds. The thing is, with the stock wiring, even when the resistor is bypassed for high current....there is a pretty good loss of current across the line.

So now the resistor would be bypassed, BUT the new wiring would allow the pump to receive the full 12-13.8v
and would give it more power to pump...
Yeah I'm sure it would wear the pump out eventually, but I only drive my car about once a week...

Does this make sense?

 

this is what you would call a fuel pump hot wire, the more voltage you give a fuel pump the more the fuel pump will flow.

 

Makes alot of sense... The more food you give a sumo wrestler the bigger he gets...lol....

 

All of my expirience comes from toyota turbo's. It is common for them to run a special "amplifier" to their fuel pumps to run them at like 18 volts. I had one on my toyota 22rte that was all done up, and it solved my lean condition (I had the injectors, but lacked flow). Has anyone done this with an FD?

 

on the fc's you almost have to rewire the pump. with the headlights on the voltage gets low at the pump. it is not a bad idea to rewire the pump. my friend did his without the resistor and the car runs fine. if it was my car (more stock) i would simply replace the factory wire and keep the resistor/wiring the same.

mike

 

alot of the 3s guys use the Kenne bell boost a pump!!!

 

I'm going to try this...it sounds like a good idea, at least until I come up with enough $$$ for a hi-flow pump...

Anyone have some ideas on how to make this work?

 

purepsi, That is the one! I could not remember the name for the life of me-thanks.

 

no problem

 

the fuel pump resistor can be bypassed

 

Ok another " TO DO " on my list...

Thanks..

Just make one HOT WIRE from the battery
to the FUEL PUMP ..

Sounds simple enough...

So you guys are sure their are no SIDE EFFECTS?
or Down sides??

How about a HOT WIRE from the battery spliced into the
factory Hotwire to the fuelpump???

 

1 side effect is that the fuel pump will not last as long due to the increase in voltage.

 

Do you know this for a fact?
Has ANYONE done a long term higher voltage test on our stock fuel pump?

Sure, there are certain things that have limits on the FDs, but certain things, like the tranny and rear end are able to support 500+hp

 

Another side effect is a Fire!

Running a hot unfused wire from the battery to the fuel pump is dangerous! If that line shorts near the tank or in the pump you have no protection by fuse.....could be bye bye 7.

 

Well I don't know why anyone would run a 'hot-wire' from the battery without using an inline fuse, it will be just like wiring up an amp for a car stereo.

As for the pump not lasting as long, I don't see why it wouldn't. It's not like we're talking about overpowering it, we're talking about giving it the true voltage from the battery...I mean that's what these things are tested on at the factory so I'm sure it will be fine.

 

the pump sees about 8-9?volts cruising around and then battery voltage after it sees 1 psi (i tested this).
you are shortening the life of the pump if you make it see 12v all the time, but when was the last time you saw one fail?? ive never seen a factory fc or fd fuel pump fail, it is something to think about but i wouldnt be worried.

mike

 

Ok, so if it sees battery voltage when we are boosting, there really isn't any sense in directly wiring it. I mean, it's getting the full amount of voltage when we need it. This could probably explain why my fuel pressure guage jumps about 10psi at boost.....

 

That's the thing...with the Mazda wiring even during full throttle when the pump is getting 'maximum' draw from the battery...the poor wiring only allows maybe 10v of the possible 13.8v to reach the pump, possible even less.

 

But j9fd3s said he tested it, and that he saw full battery voltage. You saying you tested it or these guys at that shop tested it and they only saw 10v?

****, maybe I should just test it myself when I get a chance . Hmmm...I wonder if the manual says anything about maximum voltage the pump sees.

 

Maybe it varies from car to car?...it's worth a try to test it out...you could pick up a little extra flow and not be so worried about buying an aftermarket pump...

I know this is something I'm going to look into though...