SC300 12v Fuel Mod w/ Pictures - FAQ

LyFeWoRx · 06-30-07, 02:48 PM

Mod Location:
The Fuel Pump ECU is located under the driver side rear qtr window.

Reason:
This mod is very easy - I did the mod because I was having Warm Start problems with my SC300, the car would start up then die (This would happen 10+ times in a row) This mod fixed my problem - everything works perfect now. This will also help when I go NA-T , I will have a step by step thread on that as well.

Vehicle Used:
This car is a 1992 SC300, Auto

Total Mod Time:
45 Mins

From MKIV.com

The Problem:
When modifications are made to the car to increase boost pressure and engine breathing ability, some owners have experienced detonation around 4000 rpm, as the 2nd turbo builds boost and comes on line. Usually, this detonation disappears above 5000 rpm. The problem is, the fuel pump is still in "low speed" mode around 4000 rpm's, but the performance modifications have increased fuel demand to the point of "outrunning" the low speed operation. By 5000 rpm, the fuel pump ECU has caught up and switches to high speed operation and all detonation disappears.

The Solution:
There is an easy way around this. You can wire a 12 volt signal directly to the fuel pump, effectively bypassing the fuel pump ECU so that the fuel pump is always in high speed operation. The TT Supra is one of only a few cars that has this dual mode of fuel pump operation, whereas most cars always have 12 volts to the fuel pump. This mod is completely safe. You are basically just turning your complicated fuel system into a basic, Camry style fuel system. You may shorten the life of your fuel pump from say 20 years down to 18 years, but nothing to worry about in the short term. I've personally had mine hooked up this way for over 2 years now without any troubles.

I hope this helps anyone looking to do the 12v fuel mod or starting issues.

Start with the rear seats.

Pull up on the front of the rear seats to remove the bottoms.

Rear seats removed

Remove the 3 bolts holding the rear back panel down. (12mm)

Rear seats removed

Remove 2 push tabs from the panel under the driver side qtr window.

LyFeWoRx · 06-30-07, 02:48 PM

Remove a push screw behind the drivers seat belt

Now you can remove the panel

Unclip the fuel pump ecu

All the wires going to the ecu

Clip the Green and Black/Red wires

Strip the 2 wires

Solder the 2 wires together

Tape everything up and re-install the panel and seats.

HTQCummins · 06-30-07, 04:32 PM

I like that fix. Have to wonder, who took the time (and messed up ECU's) to figure that out. Thanks for the post

LyFeWoRx · 06-30-07, 05:40 PM

It's pretty easy it has a 12v wire going in from the box and a thick wire going to the fuel pump. Both thick wires hook together. It works out though =)

Blk97SC300 · 07-02-07, 06:38 PM

Thanks for the tip. I just did this "mod", and it only took me about 20 minutes

.. I guess it's cuz I've removed the rear seat before. Easy job, and it's a good idea for anyone force inducted (like myself).

vwynn · 07-02-07, 09:20 PM

JWwhat would happen if you did this mod in a stock Sc400?

revlis240 · 07-02-07, 09:26 PM

Quote:

Originally Posted by vwynn

JWwhat would happen if you did this mod in a stock Sc400?

nothing (no gain), FPR would return the extra fuel press in the line back to the return line...

LyFeWoRx · 07-02-07, 09:33 PM

Yea it doesn't take long to do. Hope the instructions helped a little, it's very easy though.

cherplex · 07-02-07, 09:35 PM

Nice write up.

ConSynX · 07-03-07, 02:43 PM

i had this done and undid it, but i might go back and do it again, as my idle drops to like 400rpm lately, and i'm guessing it might be because of the larger fuel line. . .

curious if this relay is ONLY for the high/low turn on/off.
aka, if i do this 12v mod, will i lose the safety feature where the pump shuts off automatically when the car is off, and after X seconds of priming.

sc250tt · 07-03-07, 02:54 PM

Quote:

Originally Posted by ConSynX

i had this done and undid it, but i might go back and do it again, as my idle drops to like 400rpm lately, and i'm guessing it might be because of the larger fuel line. . .

curious if this relay is ONLY for the high/low turn on/off.
aka, if i do this 12v mod, will i lose the safety feature where the pump shuts off automatically when the car is off, and after X seconds of priming.

yea you might loose it .my car fuel pump dont shut off anymore .funny because on my 92 1j sc400 i did the same mod and it use to shut off after priming

96sc3 · 07-03-07, 05:02 PM

hmm, so is this the right way to do it?

LyFeWoRx · 07-03-07, 05:20 PM

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

Sc dRifta · 07-04-07, 02:00 AM

just fyi the 12 volt mod is for supra TT's because they are one of the few cars that run a 2 stage fuel pump which means it sends 8 volts for low rpm cruising and changes to a full 12 volt for full fuel. well our sc's dont have that so this mod is useless

mitsuguy · 07-04-07, 07:48 AM

Quote:

Originally Posted by Sc dRifta

just fyi the 12 volt mod is for supra TT's because they are one of the few cars that run a 2 stage fuel pump which means it sends 8 volts for low rpm cruising and changes to a full 12 volt for full fuel. well our sc's dont have that so this mod is useless

yes they do...