uprated fuel pump defo need constant 12v to perform at 350-400whp levels??

[jimBNR32]

plan to fit my NISMO fuel pump the weekend just in time for mapping.
i have this along with some cleaned and flow tested sard 700s and NISMO afms to match my 2860-7s for some resonable boost (1.2-1.4bar) with my powerFC.

given the size of the injectors and running these medium sized turbos, do i still need to worry about running this fuel pump at a constant 12v to get the fuel for 450-500 crank hp?? or will standard wiring hold up?
i imagine mpg with 700s isnt great, if i can help it, id rather not run them 12v all the time, lol.

if i do need to go constand 12v route, ive done a "search" and i cant for the life of me find out which wires i would need to splice/cut into specially for this fuel pump modification??

i have decent wires/4pin relay and fuse to hand, so believe i have the bits needed to make it work, but does this new wire need to connect direct to the pump (in the tank) or can i use a spade to plug into the + and - terminals on the fuel tank cap?

which wire do i need to splice into for the relay to trigger the pump to prime and work?


cheers

[GTRPower]

Just run a new trigger for the relay from ignition source (switched on by key, not accessory). Use a multimeter to find one. NISMO fuel pump should be plenty for your use, before you put it in make sure the sump is clean of debris which can be pumped in from gas station pumps. While you have the tank cover off check the fuel level sender's PCB for wear, if it looks like it's worn out or close to that, get a new one. Use the OE plug, solder the relay's powered wires onto it and use heat shrink to insulate it. Put the relay on a trunk wall, up high, away from any moisture source. Run the power from the battery, fuse it at the battery, cover the wire in a protective sheath from front to back, on the cold side (away from exhaust, you should know which side I am talking about). Use anti-chafe wrap around any bends and sheet metal edges. Ground locally, with a clean ground, no paint on surface. Do not use the OE pump power wire for relay switch- that varies in voltage based on what the pump controller sends to it (low voltage for NVH reduction on idle or below boost). That will burn out the relay prematurely.

Hope that helps.

[Skym]

Good advice in above post.

Also it's not just for reduction in NVH, but reducing heating of fuel, reducing fuel pressure at idle with stock FPR (both of them work together to reduce fuel pressure) where excess fuel is not needed.

It can start at 12V, but end up at 10V at higher rpm (not good) which result's in drop in fuel pressure, engine runs lean. Also most aftermarket fuelpumps are flow rated in lph at 13.5-14V which hardwiring fuelpump provides.

Also if you do hardwire fuelpump, you'll need to run engine richer to compensate. At least 11.4-11.5 A/F ratio to be safe or richer (into high 10's) to be 100% reliable. Why you do this, is even with hardwiring fuelpump it still drops in volts to fuelpump when aircon, lights, etc are on, ignition system sucking power, etc, so have to compensate for engine that might run lean.

[jimBNR32]

Thanks for the replies.

Many threads on the subject, well 95% of them have used the oem fuel pump wire to trigger the relay.
From what I've read it only requires a tiny amount of voltage to switch the relay, so it doesn't matter if it's in 9 or 12v mode, it'll still trigger the relay to use battery power. I read only requires 4v or so to switch, which that wire will always produce once the key is on.

If i use the oem plug for the new wires, what do I do with the plugs ground that's been cut? Simply tape it up or ground it out also??

My tuner generally tunes at 11.3-11.5 anyway, so I should be fine there.

[GTRPower]

Jim, I've given you the advice I think you sought. Since you've chosen to go your own path, good luck with your build, I have nothing else to say.

[jimBNR32]

i appreciate the reply, and i will be using the relay option exactly as you state, except im undecided on the trigger is all, hence my responce as it seems a ton of people and tuners do use that wire as a trigger wire with no reported ill effects=, just suprised to see it mentioned as a wire "not" to use.

[steveo1502]

I used the oem pump power to trigger the relay, I've heard some stories about wiring it to a switch/ignition,he got into an accident and the pump wouldn't shut off, just kept pissin out gas and started on fire, but I heard with the oem wire the ecu should shut it off in case of an accident, not really sure if this is true, I didn't really notice any difference after doing this mod.

[jimBNR32]

/\
that is indeed true, it will also prime the system exactly like stock before starting to which is also a plus point.
tho ive no idea how different that is to getting it from another power wire. :-\

[Dragon Humper]

My twins are triggered by the factory pump feed, been that way for over 10 years, no issues. I think it's better that way for a whole host of reasons. Even if the off chance that it burns out a relay, no biggie, you should be packing around a spare $5 relay anyway, Murphy Rules no matter how you hook it up.



Jon.

[GTRPower]

I like the fact some people are encouraging sloppy engineering.

Just wire your pump to the OE harness, no extra relays, nothing more than that. Your power output doesn't require anything more.

[Dragon Humper]

Thanks for sharing.

You know, this is not a take it or leave it situation. On a forum, people ask questions, they get some opinions and they make up their own mind. I happen to think (with over 25 years experience) their are more benefits than negatives to wiring the relay trigger to the pump feed, some have already put forward why that is a good idea (I could add to that but feel there is no need). You have put forth nothing other than it makes you feel icky.

Getting pissy because someone takes your ideas under advisement but does their own thing based on others opinions and the obvious volumes of reading he had already done on the subject is not really helpfull. If you want to be welcomed back by the faithfull that have contributed on here for a very long time, lecturing people instead of guiding them is not a good start.



Jon.

[jimBNR32]

I have to agree with the above, it did come across as a little pissy, but everyone has there own opinion and I appreciated the reply.

Anyway, I carried out the pump swap and 12v hardwire today.
First the pump and a test drive, then added the 12v hardwire and test drive.

Didn't noticed any driving difference on the pump swap, but Nismo pump is a Nismo pump so should do me well. Hardwire, can certainly hear the pump at idle! I've no way to measure fuel pressure, but I noticed I was running about 0.3 afr richer than before, roughly.
Car drove fine :-).

FYI, I cut the pump plug, left it in place, wired separate + and - wires onto this with the relay included and used the harness end of the cut plug to switch the relay (as is what is usually done).

Only issues, had to ask on here about how to get a wire into the trunk from the interior! I have to say removing the rear seats, altho a headache certainly gives a more race car feel and sound, especially as I'm running a hks rear cage. Can really hear the exhaust more, great!
Sadly seats will be going back in when I get round to it.

Thanks for ideas and help.

[Skym]

Fuel pressure should rise into low 40's (thanks to small orifice inside stock FPR and increase in lph of fuelpump) from stock 35.5psi at idle and get richer at mid to high rpm (into 10's with stock ECU tune) where injectors are open more, fuel pressure is higher. ECU retune fixes those running rich problems. I would suggest upgrading FPR (Nismo or rebuildable SARD FPR), as stock FPR is old and could fail.

[Supraclean]

Just run a new trigger for the relay from ignition source (switched on by key, not accessory). Use a multimeter to find one. NISMO fuel pump should be plenty for your use, before you put it in make sure the sump is clean of debris which can be pumped in from gas station pumps. While you have the tank cover off check the fuel level sender's PCB for wear, if it looks like it's worn out or close to that, get a new one. Use the OE plug, solder the relay's powered wires onto it and use heat shrink to insulate it. Put the relay on a trunk wall, up high, away from any moisture source. Run the power from the battery, fuse it at the battery, cover the wire in a protective sheath from front to back, on the cold side (away from exhaust, you should know which side I am talking about). Use anti-chafe wrap around any bends and sheet metal edges. Ground locally, with a clean ground, no paint on surface. Do not use the OE pump power wire for relay switch- that varies in voltage based on what the pump controller sends to it (low voltage for NVH reduction on idle or below boost). That will burn out the relay prematurely.

Hope that helps.

Great info, this is exactly the info i was looking for.

My question is what size of wiring should a guy use for running for the relay?

Also the fuse used would be a 15 amp or higher if running constant voltage?

[mptjimmy]

the soarer and supra use a 10v idle, 12-13.5 at rpm to help idle gas consumption