SC300 12v Fuel Mod w/ Pictures - FAQ - Page 2

mitsuguy · 07-04-07, 07:59 AM

Quote:

Originally Posted by LyFeWoRx

Yes, or you can run a 12v wire from the battery to a relay then to the green wire on the fuel pump.

if you really want good voltage, this is the real way to do it... a very very common mod on the DSM's - the stock wiring wasn't enough for an aftermarket fuel pump to get the full voltage possible... run an 8 gauge wire from the battery terminal back to the fuel pump... install a relay using the green/red wire from the fuel pump ecu as the switch for the relay, and then use a short amount of the red/green wire coming from the fuel pump to go to the relay....

voltage drop over 20 feet of small gauge (whats it - 14?) wire drops voltage all the way back to the fuel pump...

ConSynX · 07-04-07, 09:16 AM

dont use the stock wiring for the fp if you are needing 8ga supply.
i was using 10ga supply, and then the stock green wire or w/e, and the wire melted. . .
my new plan is to run the second pump only off a new wire, and tap INTO the existing wiring of the fuel pump to trigger a relay. . .
i'm not having fuel problems really, the car goes lean for about 0.5seconds when i hit the gas, then the pump gets 12v

mitsuguy · 07-04-07, 09:20 AM

Quote:

Originally Posted by ConSynX

dont use the stock wiring for the fp if you are needing 8ga supply.
i was using 10ga supply, and then the stock green wire or w/e, and the wire melted. . .
my new plan is to run the second pump only off a new wire, and tap INTO the existing wiring of the fuel pump to trigger a relay. . .
i'm not having fuel problems really, the car goes lean for about 0.5seconds when i hit the gas, then the pump gets 12v

really- on the dsm's, we used the 4-5" worth of stock wiring with 8 gauge feed and no problems even on the walbro 255hp

ConSynX · 07-04-07, 10:17 AM

i was splicing in tank to run two walbros.
don't really need to change the wiring for a single walbro. . .

mitsuguy · 07-04-07, 10:29 AM

Quote:

Originally Posted by ConSynX

i was splicing in tank to run two walbros.
don't really need to change the wiring for a single walbro. . .

I disagree...

all fuel pumps flow significantly more at higher voltage... the stock wiring has a little more than 1 volt drop at 17 amps (the max current draw of a walbro 255 pump) stock charging system should be around 14 volts at the battery, by the time it gets to the pump, you are at or below 13 volts... at 12 volts, the 255Hp flows 58 gallons per hour at 40 psi, but at 13.5 volts, it flows 68 gallons per hour...

going to a 8 gauge wire decreases voltage drop to .15 volts, so, it's worth 6-8 gallons per hour increase in pump capacity on the Walbros... seems to be worth it to me...

without the wire upgrade, you are effectively running a 220 lph pump...

ConSynX · 07-04-07, 08:00 PM

touche salesman.

i was not considering the resistance of the wire itself...

ltbong · 07-15-07, 09:16 AM

So if my fuel pump ecu is bad I can do this to bypass it and get my car running again?

Will the fuel pump shut off when the car is off?

LyFeWoRx · 07-15-07, 11:42 AM

Mine shuts off just fine. Everything is still working fine. No hard starts anymore.

clevercat · 07-16-07, 01:13 PM

300ZX TT also uses the dual stage (low & high) pump controller computer located behind the driver seat so Supra TT is not only one.

The fuel mod is fine.
Just bypass the fuel controller and use the OEM wires.
This mod would slightly reduce life cycle of your fuel pump.
Not a big deal.

I agree with mitsuguy

By the way, why would you want to put walbros fuel pump in SC???

I rather install the reliable Supra TT fuel pump.
It would give you as much fuel as you need if you are not running less than 800+ HP. If you want more fuel, get another TT fuel pump and dual feed it.
You would run out of gas money before your engine runs out of fuel

By the way, it is highly recommended to get the fuel pressure gauge before doing any fuel system mod. At least, you would know what your system is putting out before blowing up your engine!

assasin123 · 07-16-07, 03:18 PM

i would agree a guy early, i don't know if this mod is beneficial to sc300. i hook up my voltage meter and voltage reading is 12v on ignition on, and remain 12v through out 1000rmp to 5000rpm. i am curious if any body has a dyno number to prove this theory once for all. so for now, my is stock with walpro, no idle issue at all , 1jz soarer.

mitsuguy · 07-16-07, 03:44 PM

Quote:

Originally Posted by assasin123

i would agree a guy early, i don't know if this mod is beneficial to sc300. i hook up my voltage meter and voltage reading is 12v on ignition on, and remain 12v through out 1000rmp to 5000rpm. i am curious if any body has a dyno number to prove this theory once for all. so for now, my is stock with walpro, no idle issue at all , 1jz soarer.

it's not about a dyno number... it's about running out of flow on the walbro's...where is that 12v measured? at what engine load - free revving?

the walbro's are only going to be stressed under high load, even at 5000 rpm, if there is no load on the car, then fuel requirements are barely above idle...

also, if you look at the flow sheet I posted above, you will see that at 12 volts,
the pumps supply far less than they do at 14 volts, which is what a proper vehicles charging system should be at...

mitsuguy · 07-16-07, 03:46 PM

Quote:

Originally Posted by clevercat

I agree with mitsuguy

By the way, why would you want to put walbros fuel pump in SC???

I rather install the reliable Supra TT fuel pump.

only reason to do the walbro is the really high flow rate, and cheapness...

also, I haven't ever heard of a walbro pump actually dieing ever...

but yes, the Supra pump would be ideal, nothing like OE reliability, they can be pricey however

clevercat · 07-16-07, 07:43 PM

OK, here is my Dyno chart.
Boys and girls, this is what we are talking about.....

As you can see, I have problem right before, during and right after the big turbo is on! It becomes stable as soon as both turbos are fully boosting.

Actually, my engine ran lean during transition!
Scary!

The Supra TT fuel pump is capable of supporting up to 800 HP.
I am going to dual feed TT fuel pumps (like my Z32TT) when I single it.
That's all the fuel I need.

I rather bet on TT fuel pump than Walbros.
Especially, when I am boosting requiring more fuel.
I rather spend little bit more money than blowing up my engine.

I am correcting this transition problem by installing the AFC and tuning it.

vntperform · 10-05-07, 12:48 AM

I noticed today on my 2jz-GTE equiped 97 sc300 that when I removed the panel in the rear quarter glass that the fuel pump ecu was disconnected. But the car runs perfectly fine, any idea on why this might have been done?

-v

mitsuguy · 10-05-07, 06:58 AM

Quote:

Originally Posted by vntperform

I noticed today on my 2jz-GTE equiped 97 sc300 that when I removed the panel in the rear quarter glass that the fuel pump ecu was disconnected. But the car runs perfectly fine, any idea on why this might have been done?

-v

ummm, sounds like someone has already hotwired it for ya...