FD3S Fuel Voltage Low, Resistor
 

I have low voltage to the fuel pump. 6V at idle and 9v at rpm.

would it be best just to rewire it for 12V all the time or to replace the voltage regulator?

at 12V all the time It would put more wear on the pump at idle but has anyone had a fuel pump go out due to this?

Thanks,

Kevin

I did the rewire mod to mine and it's great now. Before when I had only 6v to my pump the power would plateau at around 300whp on a freakin 500R, now I'm getting a lot more. I'm even using a Kenne Bell BAP and it still wasn't giving me any extra voltage before the rewire. I'll see if I can find the pic of the wiring diagram I used. It's really easy though. Wire it straight off the battery to a relay and put it in line with the wiring that's already there so it shouldn't put any more stress on the pump than what was meant to be there in the first place. Although if you don't have a relocated battery this may be more labor intensive than some other rewiring methods.

OK found it.

And here is the description...

I just did this on my FC, WOW what a difference. I used to get 8v cruising, and sometimes it would drop to 7v in boost, with a max of 10v.

I chose to keep the voltage regulator and relocate it to the rear near the pump running new wires directly from the battery to a new relay, to the regulator to the pump. I did this because I am still on the stock turbo so its not that crucial to have 12v all the time. This is also my daily so having some fuel economy would be nice as well.

Now I see 10v cruising and 13.5 wot!!!

To answer one of the original questions; I believe David Haynes (20b fd) has burnt up a pump running 12v constant, and it didn't even take that long. He was running dual pumps though, ,so I'm not sure if the additional amps played a significant role.

As far as I know, the way I wired mine won't give it 12v constant because it still goes through the stock wiring, so it still has the two speed function. I think it just makes sure that it has 12v available when it's needed, but I suck at electrical and wiring so it's hard telling if that's true haha.

10ga is too much unless you're running it from the battery. 10ga is good for about 40A, A bosch draws ~13A, a Denso takes about 16A iirc. Mind you, running it from the battery and more importantly BACK to the battery is the best way to go about it.

If you've got a standalone and can tune it, or don't mind running a little rich under cruise, ditch the voltage reg and wire it strait. One less thing to fail.

You're thinking about it backwards. The more voltage you give the pump, the less A's it needs at the same pressure. So, you won't burn the thing up running it constantly. My pumpS see running voltage minus about .2V and I've run them for 21 hours pretty much strait. If he burned out a pump while running dual intanks, my first guess would be insuffiecent wiring, both in size and voltage. The smaller wiring will create resistance, the two pumps pulling more A's than it should causing heat. Heat causes more resistance, and it just becomes a downward spiral untli the V goes too low, the A's go to high, and then they burn up

I have an rtek 2.1, which is based on the stock map (which accounts for bi-voltage operation). It does have fuel adjustment which I could use to lean it out but....why? I'll let Mazda figure out the fuel economy (this is a daily) and I'll spend my time refining the boost portion. As far as failure, I've found one case of either the resistor or relay failing....I like my odds :icon_tup: But when the time comes for me to sell a kidney and get a Motec, I'll rip out everything stock I don't need and rely on the ecu.

Ahhhhh! I've never liked electronics, at least the planning/understanding part. Guess I'll have to bust out those old physics books....I make some damn sturdy connections though,lol. I don't remember the details of his setup, simply that a pump was burned up.

The FPR will take care of most of the difference as far as tuning goes.
Mazda doesn't always do the best job of economy. I have a friend of mine, we went out and street tuned his Rtek one night and he got something like 28mpg on the way up to canada. Now, granted this was an n/a but I never got close to that when I had a ecu.
Bottomline is, using the stock Rtek map is a weak excuse for wanting to keep a voltage reg. Lower voltage means higher amps, I'm not sure why Mazda did it that way, but I don't think it's needed, therefore it goes away.


First time I've heard of a pump burning out for no reason, there must be a reason...... could be low voltage caused by a bad voltage reg :D

Well, before all these fuel related problems and subsequent upgrades I got 17/25 like clockwork. I'm just trying to get back there, I'll tune the rtek when I get a chance and hopefully I can shoot for that 28mpg mark. At least now I don't have to get 13mpg while I wait.

"You" don't think its needed. "You" would also work 48 straight hours for the privilege of driving another 14....:suspect: "You" would also spend the time/$ to fine-tune the drivability portion of your map to near perfection. "I" don't possess the resources in $, skills, or patience to commit to doing that at this time. what "I" know is that of all the FC people (not running a stand alone.....and most who are) who have re-wired their fuel pump for constant 12v do not get acceptable fuel mileage for a daily driver. Lol.


:lmao: could be, I don't know anything about the FD voltage regulator....apples to oranges.

46 hours straight.... gonna try to break the 2 day mark this time around.

A voltage regulator is only slightly related to fuel mileage, the FPR compensates for most of it.

Think of it this way.... constant 13v+ is going to draw less amps and create less load/heat on the pump. That alone is reason enough for me. Tuning for fuel economy is pretty damn easy, just takes two people and a few hours cruising around.... or datalogging.

I have been reading on fd3s.net about this:

Low speed is active at idle and under 3K rpms through the fuel pump resistor fed through the main relay. High speed runs through the fuel pump relay which the ecu controls; the fuel pump relay supplies battery voltage to the pump when it is closed. The ecu toggles this relay so the ecu actually controls the fuel pump speeds.

Does the PowerFC have a setting that can control this?
What other fuel pump relay are they referring to ? is it the relay Mounted on Left Inner Fender in the wide Relay Box

Look in the FSM and you will see the circuit opening relay which supplies the 12V to the pump(located in the left fender box) and the speed relay(located in the front box).The PFC handle them as the stock ecu does.

I rewired mine to run exactly like stock buy installing a chassis ground near the pump, and some parallel wires. This increased the votage to the pump from 11.8 to 13.8.

Re wire it mate,

I have a Sard 280lt DENSO pump with rewire and BOOST A PUMP in mine and its perfect.

upgraded fuel pumps pull additional amperage, single stock fuel pumps running stock battery voltage levels may never see the connector on top of the fuel pump burn up but i do suggest doing the bulkhead connector modification when upgrading the fuel pump and/or rewiring it for higher voltage.

the FC S5's had the small 4 pin junction connector on top of the fuel tank as well as the FD and both have issues with that connector melting down when pushing too much juice through it. i have yet to see an issue with the S4 fuel pump housings. i have also had one customer who had his housing connector melt down with his walbro255 in his firebird superchicken WS6, had a similar connector to the S5/S6 tank connector styles.

bulkhead, bulkhead, bulkhead. do it in conjunction with upgrading your fuel pumps.

on the upside, the connector melting down usually won't take a motor with it but it will leave you stranded on the side of the road with a car that won't start.

anyone with a standalone should do both the rewire and bulkhead connector modification. if running the stock ECU still on an FD you can rewire the fuel pump to push better voltage through the relay by wiring the factory relay directly to the battery.