R33 Fuel Pump Wiring , Better Feed Retaining Fpcm ?

[GTSBoy]

correct, hence the negative triggered relay for the full voltage..will have beefy earth wiring.

on idle, the current is very low as the fuel pressure is only at 3bar, theoretically only max of 15AMP (which the stock wiring will handle)..

so how it will work

fuel pump

+ ve: 40AMP relay & 25AMP fuse with 12ga wiring

- ve: 2x negative feeds, 1x stock low voltage for idle & 1x 40AMP relay & 25AMP fuse with 12ga wiring for full noise, triggered by the FPCM.

Fair. I was just working on the last part of your previous post that said you'd be "using" the original negative side wiring. I realised you were putting relays in that side, but didn't know if that meant all new wiring or re-using the original skinny stuff and hooking it up to the relay. I know it sounds retarded to suspect you of being retarded, but I couldn't help myself.

Edited January 6, 2014 by GTSBoy

[Dose Pipe Sutututu]

^ hahahah we are all retards, just half retard OR full retard...

I might be overcomplicating this shit, because slow or fast or whatever the fuel will heat up regardless from the rail

[Adriano]

But how much of the heat comes fromthe pump itself, if it is drawing 20A at full noise, thats 240watts, introducing o lot of heat

[Dose Pipe Sutututu]

Hopefully I'll get this one sorted by next week.. waiting for Ricky to pass on the factory resistor pack & some factory connectors so I can start.

I want to leave the original wiring there intact just in the event something in my setup fails I can plug up the old wiring and drive home.

This is how I have the setup mapped in my head.

Relay 1:

Battery -> Fuse -> Relay -> +ve fuel pump

Trigger sourced from the original trigger (pre factory relay, so even if the factory relay dies it will still fire)

Relay 2:

Ground -> Relay -> -ve fuel pump

Trigger sourced from FPCM (it's a negative switch so I will bridge the other pin to an +ve source)

Factory Resistor Pack:

Ground -> Resistor Pack -> -ve fuel pump

The idea behind this setup, is that the fuel pump will always go through the resistor pack. However when the FPCM clicks over, the fuel pump will be grounded to get the full 13.8V

By doing this, I am pretty much mimicking the factory setup however with 2x 40AMP relays 12ga wiring and a nice 30AMP fuse instead of telephone wiring and 15AMP fuse.

[Ben C34]

Looks like a plan. I like it.

[Dose Pipe Sutututu]

Shit got real, all working as planned. Just one small hiccup, had to cut the output wire from the fpcm as it was bridged to the ground which kept firing off the 2nd relay.

All sorted, just need a bracket to tidy things up. One thing I noticed, the resistor pack gets so damn hot due to the current draw. I might make my own or use one from a fan blower controller.

[Dose Pipe Sutututu]

Alright, so the stock resistor gets stupid hot because of the current draw in my setup.. I've worked out I want the pump to drop to 12V, which means I would need to drop the voltage by 3.8V

At 3 bar pressure, the pump requires 13.52 amps of current

Using R = V/I to work out the resistor I would need, R = 3.8 / 13.52 = 0.28 ohms

Using P = VI to work out the wattage I need to dissipate, P = 3.8 * 13.52 = 51.4 watts

So ideally the resistor would be close, the closest I found was 0.3 ohm resistor that dissipates 50 watts.. comes in a funky heat sink too!

If you guys are using large pumps with the factory resistor pack, I suggest you ground off your pumps now before you set your car on fire!

[discopotato03]

Really what this all comes back to is the current draw of the pump and the cars wiring is made to live with the standard pump .

Aftermarket pumps draw high current because I don't think they use very efficient pump motors . One of the easiest solutions is to use the GTR Nismo pump because it draws less current for its capacity than many aftermarket ones , and it's obviously intended to cope with a standard GTRs wiring .

I think there has to be better ways than trying to use the factory system with higher current draw pumps than the std or Nismo ones . If you go the traditional way with high capacity wiring and no current stepping you get the fuel heating issues because everything goes through the hot bay/rail .

I still have to wonder what happens if you run a second bypass , literally another std or equiv regulator , upstream of the rail and plumb it back into the existing return line .

Yes the high capacity pump runs flat out with low resistance wiring all the time but the fuel loop so to speak can bleed something like half the volume back to the tank with half the fuel flow resistance . I can't see a problem with having two std capacity regs and the advantage is that one feeds back into the return line BEFORE the hot rail end of the fuel loop .

People may think yeh but what if that other reg fails open , well that's about as likely as the std one doing this and the results is the same . Rail or similar mounted regs live in a hot vibrating environment and most people reckon both ultimately don't do them any favours .

I think pump motors add sfa heat to the fuel compared to the rail and engine because they don't have a real lot of thermal mass to start with .

Anyway I reckon the "pre rail 2nd reg" , PR2R , deserves some thought . The only reason that return line EFI systems regulate from the rails return is to give boiled fuel vapours in the rail an escape path so you can start the bastard hot ie after a bit of heat soak .

IMO it shouldn't matter if you have one reg two regs or ten regs , if they are referenced off manifold pressure they should do about the same thing and if any is a tad low pressure wise it achieves the same thing as if that was only reg in the system pressure wise .

I can't think of any other cheap simple way of solving the wiring and fuel flow/heat problems .

Thoughts ? Cheers A .

[Dose Pipe Sutututu]

Well think of it this way, at full song (at idle) that walbro 460L fuel pump is essentially a ~210watt fuel tank heater, when the voltage is dropped to 10V (guessing current draw would be ~12amps) you'll essentially only have a 120watt fuel tank heater

All my wiring, relays, fuse holder & resistor has set me back no more $40

And it works like the factory system, switching from 10V to 13.8V


So I don't know what you're going on about "I can't think of any other cheap simple way of solving the wiring and fuel flow/heat problems" I just solved it for you

[battery]

Im no expert when it comes to DC fuel pumps but i do know that many electric motors will run cooler at the full voltage they are rated for and usually when you under volt them the current increases to compensate.

http://www.motorsanddrives.com/cowern/motorterms12.html

Personally I'd prefer to run at the full voltage and try cooling the fuel by other methods.

[GTSBoy]

Once you get to the point of worrying about fuel heating, you really should just bite the bullet and put a cooler in the return line. Got to be the easiest way to short circuit all the other problems.

Having said that, any in tank pump that is drawing heaps of current is of course an in tank heater so taking care of the FPCM stuff is not a dumb idea. The reality is though that pretty much the only time it's not on full power is when it's idling at the lights, so it probably doesn't save a lot of heat in day to day stuff.

Adrian's 2nd fuel reg idea is a valid one. I've previous thought it would be a good way to achieve the goal. But again, there's a small problem. Because 2 regs will never be set at the same pressure, the one that is set lower will be the one that will be open and returning. If each of the regs are large enough to handle the full flow, then the lowest set one will be the only one flowing. Depending on your point of view, this would be either be fine or it would be a problem. If the upstream (bypass) reg is the low set one, then the minimum amount of return fuel heating will occur, but the rail will be working dead headed and so you might get hot restart problems (and just hot fuel in the rail in general in normal running). If the rail mounted reg is the low one, then the upstream one is doing nothing, so no benefit. Getting them both control to exactly the same pressure might be doable. If the pump capacity is large enough that you have too much flow for one reg, then you're probably golden. I know from personal experience with gas regulators (for natural gas on industrial installations or the Olympic flames jobs we do) where we have two reg sets in parallel, it is almost impossible to make both sides flow at the same time unless they are undersized compared to the duty and therefore not able to keep up on their own.

[Dose Pipe Sutututu]

interesting, I'm dropping the voltage by 16%

I'll plug up an ammeter and see how much it's actually drawing

[Ben C34]

Im no expert when it comes to DC fuel pumps but i do know that many electric motors will run cooler at the full voltage they are rated for and usually when you under volt them the current increases to compensate.

http://www.motorsanddrives.com/cowern/motorterms12.html

Personally I'd prefer to run at the full voltage and try cooling the fuel by other methods.

I thought the same thing, but there is a chart that shows the pump consumes less current at a lower voltage, not sure how or why though.

[discopotato03]

Except that all the fuel is going through the fuel rail and I bet its putting more heat into the fuel than the pump is in 9v mode . Primary current mode is intended to work with what the standard pump moves with 9v . GTRs take it a step further with two resistors and two stage switching ie both or one or none . From memory their low load pump voltage is more like 6.5v and I'm pretty sure a 460L pump is moving more at 9v than a GTR one is at ~ 6-7v .

The OE system literally burns off the reduced voltage as heat because it's a cheap means of doing so not a good one . You're talking valves in ancient TV sets to reduce current so really pre historic . Bypassing the at times unwanted extra fuel capacity isn't exactly elegant but I thing simplicity on the electrical side would make for better overall reliability . How often do you hear of FPRs (OE ones) failing ? They are a simple dumb device with two fuel and one vacuum hoses so no relays resistors fuses etc to fail/burn out .

Don't need any fancy high volume obviously non standard regs to scream modified and mounting/hiding an OE type , someones OE type , reg down near the fuel damper in an R33 won't attract any undue attention . If you can source the pressure tap off the back of the plenum the Vac hose won't be terribly long .

I also reckon with little resistance to flow through two regs the pump won't draw a lot of current at light engine loads because the pump won't see much load .

Just food for thought .

[Dose Pipe Sutututu]

^ base fuel pressure is 3bar, at 3 bar & 13.8V these Walbro E85 pumps like to have ~15amps of current

even with your dual reg business, let's say now the rail pressure is at 1.5 bar (I doubt injectors would like it, but for argument sake), Mr Walbro e85 would still want 14 amps of current...

[battery]

Best way to sort this out would be to install a few temp sensors and find out where most of the heat is coming from. Intank, on fuel pump, rail and return line would do it.

[Ben C34]

I strongly considered this two or more speed pump thing, but haven't had an issue to prompt me to do it.

I am more likely to fit a fuel cooler on the return line for simplicity and actually cooling the fuel, not just heating it up a little less by dropping pump voltage.

[Ben C34]

Also on the two reg thing, couldnt you replace the reg on the rail with a small restrictor (preferable adjustable) then returning to the return line, and then use the reg mounted close to the pump to control the pressure. I think trying to get 2 regs to work would be tricky, this way some fuel will be returning from the rail no matter what.

[GTSBoy]

A fixed (even if adjustable) upstream orifice leak solves nothing. It just reduces the capacity of the pump by the amount that "leaks" back uncontrolled. It needs to be a reg to offer anything, subject to the problems I outlined above.

[discopotato03]

I look at it like this , a 460 Walbro is capable of probably double or more what a standard R33T pump is and the std reg is designed to cope with std pump return volumes .

If you double up on the regs then you have twice the regulator capacity to deal with very high flows at idle etc . If one of them returns fuel in a cooler environment then the heat issue won't be so great . People like scotty say the std regs have quite small bypass passages in them which is why they very likely don't cope too well in single form with a 460L/min pump .

Twice as much pump and twice as much reg capacity . They may regulate at slightly different pressures but with the volume you are talking about I think you would always get flow through both . I suppose you could place a slight restriction (drilled piece of 8mm bar inline) at the rail outlet one so the upstream one is doing most of the bypassing and could experiment with hole sizes . FPRs can always close up to maintain fuel pressure but once fully open they can't pass any more regardless of rising fuel pressure from big pumps .

All this assumes you need a Walbro 460 BTW because if you can't use most of its capacity the bigger pump side affects and electrical current draws are for shit .