Supra Forums banner

1 - 20 of 21 Posts
L

·
Guest
Joined
·
0 Posts
Discussion Starter #1
I was reading about this as an upgrade....

What are the advantages of this?
Why did toyota not do this from the factory?
And how do you do this upggrade??>

THANKS
 

·
Be original, not a copy
Joined
·
861 Posts
Main advantage is that you loose the "stumble" that sometimes happens on the transition from ~8 to 12 volts, especially if you have upgraded ANYTHING. Plus, if you are running an aftermarket fuel pump (Walbro) then you really do need a constant 12 volts. They don't like to run less voltage, you can do it, but they don't like it. Toyota may have done it to prolong fuel pump life or simply because the higher volume is not needed in low demand situations so instead of bypassing the extra fuel just do not pump it.
If you do the mod then you really should remove the restriction in the return "J" pipe (on the side of the block). The easiest way to do it is to "jumper" the two wires at the fuel pump resistor. The other option (better for performance) is to run a dedicated 12 volt feed back to the fuel pump and use a dedicated relay that is switched by the stock feed wire.
 

·
Premium Member
Joined
·
5,894 Posts
DeanMarcum said:
Toyota may have done it to prolong fuel pump life or simply because the higher volume is not needed in low demand situations so instead of bypassing the extra fuel just do not pump it.
Thats exactly why the did it..... you are flowing about 20% more with the pump bumped to 12vdc. Also the stock injectors never need that much flow to operate on the stock fuel system. So its all good. You wont gain anything with this mod if you are completly stock. Only if you have Exaust/Intake ect. ect.



Trey
 

·
VIVA LA M.A.S.H. Midwest
Joined
·
1,451 Posts
DeanMarcum...
jumper wire?
Errr?
I was just told to unpulg the resistor on the pass side, under the hood next to the Abs system block.
Wala.
12v fuel pump.
 

·
Be original, not a copy
Joined
·
861 Posts
mdcmotorsports said:
DeanMarcum...
jumper wire?
Errr?
I was just told to unpulg the resistor on the pass side, under the hood next to the Abs system block.
Wala.
12v fuel pump.
If you just unplug the resistor you will have an "open" circuit. The car will start but then die. On startup the ECU bypasses the resistor and sends 12 volts to the pump but once the car is running the ECU "turns on" the resistor and if you just have it disconnected the fuel pump will shut off. You need to jumper the plug wires on the harness.
 

·
Premium Member
Joined
·
5,894 Posts
DeanMarcum said:
If you just unplug the resistor you will have an "open" circuit. The car will start but then die. On startup the ECU bypasses the resistor and sends 12 volts to the pump but once the car is running the ECU "turns on" the resistor and if you just have it disconnected the fuel pump will shut off. You need to jumper the plug wires on the harness.
No you dont. The resistor is only in line to cut current. If you remove the resistor the + volts pass thorough the relay. By putting a jumper on there all you are doing is bypassing the relay...... Not a good idea.

Trey
 

·
Registered
Joined
·
22 Posts
Hey guys

So would it be better if I unplug or jump the wires? Thanks for the help guys. Its weird I was reading on this also a couple of days ago and was wanting to do it but didnt have enough info.

Thanks again:D
 

·
Be original, not a copy
Joined
·
861 Posts
Just went down and verified: if you unplug the resistor (2 wire connector) the car will start and then shut off. It is an open circuit, confirmed on the wiring diagram as well. If you jumper the 2 wire resistor it does nothing to the relay it just passes zero, or minimal, resistance to the circuit during the ECU "low volt" mode.
 

·
Impeller Head
Joined
·
2,832 Posts
Dean is right. I tried this before. The relay is normally at 12 volts connection. As soon as the ECU sends the FP signal to the relay(ie: at idle) it switches to the low volt, if the resistor circuit is left open, there will be no power to the pump. If the resistor circuit is jumpered, the relay still switches to and from the two relay terminals but both will be 12 volts.
--Ron
 

·
Registered
Joined
·
1,437 Posts
I run my Aeromotive pump thru the factory relay and have the resistor gone and a jumper wire in where the resistor used to be. As Ron stated the ecu still switches it's just 12 volts on both sides.
 
L

·
Guest
Joined
·
0 Posts
Discussion Starter #11
So just remove the resistor , and connect the wires back toghter??


OKay where is this resistor located??
 

·
Be original, not a copy
Joined
·
861 Posts
Exhaust side of engine bay, right by the fuel pump relay. Looks like a silver box with fins on it, 2 wire connector. The four wire connector goes to the fuel pump relay. You want to jumper the two wire connector, just leave the resistor sitting there (it is attached to the relay braket).
 
Y

·
Guest
Joined
·
0 Posts
Discussion Starter #14
thats way easier than what it takes on my friends rx-7...sweet
 

·
2/3 HP to the Paws
Joined
·
1,519 Posts
The variable pump power exists for two primary reasons: To extend the life of the pump somewhat (it's pretty marginal), and to keep the fuel from picking up extra heat from the pump.

That's all well and good in a stock situation, but with more boost, there are really no advantages and a lot of disadvantages to running variable power.

The ideal way to power the pump is to run some heavy gauge high quality audio power wire directly from the battery, then through a fuse and relay to power the pump. Then, switch that relay with the stock power source.

That way you'll get ~13.5 volts to the pump and get the most flow out of it.
 

·
This Is Why I'm Hot.....
Joined
·
1,984 Posts
Hello Guys,
With the Walbro, J-tube gone with -06AN ret line to firewall, & oem FPR on 550s, I could not run full time 12V. Even with VPC/GCC cranked back, it ran too rich at idle/low rpms. I would advise this mod only for those running an AFPR. Dial it in so idle FP is the same as it was, & minimize additional tuning.

Take care.
 

·
Registered
Joined
·
3,413 Posts
Good point Lar.

Also, the pumps can deliver more flow with higher voltages. Running a Walbro at 15V would be interesting. Would be interesting to see how long it'd live when pushed.

At a minimum, all aftermarket pumps would benefit from a quality fat power AND ground wires. If your stock wiring drops the pump to 11V back there, you WILL NOT get your moneys worth.
 

·
Moderator, l337 M0d3r4t0r
Joined
·
12,222 Posts
Lar, I have 50 base pressure 550 cc injectors, j restriction gone, 12 v and I've managed to get idle to normal!?!

I do however have the adjustable throttle body from the 87 I just adjusted my screw out... i'm sure you 89's must have it but it's capped like the Lexus AFM screw!
 

·
This Is Why I'm Hot.....
Joined
·
1,984 Posts
ZaZZn said:
Lar, I have 50 base pressure 550 cc injectors, j restriction gone, 12 v and I've managed to get idle to normal!?!

I do however have the adjustable throttle body from the 87 I just adjusted my screw out... i'm sure you 89's must have it but it's capped like the Lexus AFM screw!
Hello Eric,
A couple items.
One, the screw on the TB was never meant to adjust idle. If you are using it, it screws w/the TPS. It's my understanding it was originally meant to adjust for minute fluctuations to vacuum applied to the EGR vac-ports within the TB. Bottomline: Can it be used to alter idle? Yes, Should it be used? No.

Two, your car is not my car. At a reference pressure* of 43psi, losing almost 30% AFM signal by way of knobs still had TCCS whacked. Oh, I could get it to idle smoothly, but smoothly doesn't mean AFs & TCCS were happy.

I'm neither condemning your chosen method, nor condoning it. If anything, our collective experiences should illustrate to those who delve into fuel mods, that EVERY car is unique unto itself.

Take care.


*Reference pressure is measured w/o vacuum applied to the FPR.
 
1 - 20 of 21 Posts
Top