12
VOLT FUEL PUMP MOD

Click Here for illustrated instructions

The Concept

The stock fuel pump on the twin turbo Supra has two modes of
operation.   There is a high speed mode for high engine demand, and a low speed mode
for cruising.  The fuel pump ECU(seperate from the main ECU) receives information
from the main ECU which determines which mode the fuel pump should be operating in.  
Various sensors come into play to determine when high and low speed operation should be
used.

Under idle conditions and cruising, the fuel pump ECU sends
a reduced voltage output to the fuel pump(9 volts), and the fuel pump operates in
“low speed”.  When engine sensors determine a high engine load, the fuel
pump ECU will send a full 12 volt signal to the fuel pump, kicking it into “high
speed” so that it will supply more fuel.

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.

The fuel pump ECU is located in the trunk
area(Fig 1).  Pop your hatch, and look for the trunk courtesy light on the driver
side plastic paneling by the rear shock tower.  The fuel pump ECU is bolted to the
body, under this panel.   To access, pull back the carpet.  You will expose a
black piece of styrofoam on the left side of the spare tire.  Remove the spare and
pull out this black styrofoam, it is only velcroed in place.  Once the styrofoam is
out, you can reach up under the plastic and feel around for the ECU.  It is about
4″ x 6″ x 4″.  There will be an electrical plug on the side of the ECU
closest to the tail light.  Unplug this plug.  There will be enough slack in the
wires to pull the plug below the plastic paneling for easy viewing.  There should be
a blue wire with an orange
stripe.   Note that for
1997
this wire is solid blue, on
1998
this wire is black with
a red stripe. – verify which wire applies to you before you
proceed.   This is the 12 volt power
supply for the fuel pump ECU.  It is only 12 volts when the ignition is in the
“on” position and has a fuse in the closer to the battery.  This will be
the new supply for the fuel pump.  There should be a blue wire with a red stripe. 
This is the output signal from the fuel pump ECU to the fuel pump.  Cut the blue/orange wire and
the blue/red wire and connect these two together.   You now have 12 volts wired
directly to the fuel pump.  use electrical tape on the two wire stubs still connected
to the fuel pump ECU so they can’t short out on body ground.  Make sure you use good
quality electrical connectors so the fuel pump doesn’t see an intermittent signal or short
out on body ground.  Plug the connector back
into the Fuel Pump ECU.

Fig 1
.

Email me
  (Brian B.)