FD3S Fuel Voltage Low, Resistor

[Sharingan 19]

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.

[TitaniumTT]

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.

Originally Posted by Sharingan 19

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.

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.

Originally Posted by Sharingan 19

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.

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

[Sharingan 19]

Originally Posted by TitaniumTT

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.

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 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.

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

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.

[TitaniumTT]

Originally Posted by Sharingan 19

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 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.

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.

Originally Posted by Sharingan 19

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.

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

[Sharingan 19]

Originally Posted by TitaniumTT

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.

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.

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.

"You" don't think its needed. "You" would also work 48 straight hours for the privilege of driving another 14.... "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.

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

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

[TitaniumTT]

Originally Posted by Sharingan 19

"You" don't think its needed. "You" would also work 48 straight hours for the privilege of driving another 14.... "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.

[Rotary Evolution]

Originally Posted by Sharingan 19

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.

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.