Monday, November 24, 2014

DIY Fix: How to Install a Greddy Boost Cut Controller (BCC) on a 2JZ-GTE with VVT-i (Lexus GS300/Toyota Aristo)

A Greddy Boost Cut Controller (BCC) will allow you raise the boost pressure without hitting the factory boost cut.
Our project Lexus GS300 (Toyota Aristo) has been running great, and we love the flexibility of the VVT-i 2JZ-GTE engine around town.  Boost comes online at 1500 rpm in sequential operation to provide adequate torque, and the 2nd turbo comes on at about 4200 rpm to provide additional power up top when needed.  We switched the car to a parallel setup aka True Twin Conversion (TTC mode), which has a bit more lag with the turbos providing boost starting at about 2800 rpm, but there is no dip in power between 3800-4200 rpm when the 2nd turbo would spool up in sequential mode.  This gives the car a more linear feeling powerband with more midrange punch, albeit at the expense of low end torque. 

We recently installed a bleed valve style manual boost controller to increase the boost from the factory setting of 12 psi.  One thing we noticed with the installation of the boost controller was the immediate increase in low end torque.  Noticeable boost (~5 psi) would come in at about 2200-2400 rpm depending on the gear we were in, which made our GS300 much easier to drive around town at low speeds.  We wanted to set our boost to 16 psi, however we were running into boost cut at 14.7 psi (1 Bar) of boost.  Boost cut is a safety feature where the computer cuts the ignition to the motor if the manifold pressure exceeds a certain threshold (1 Bar in our case with the 2JZ-GTE engine) for more than a second or two. 

To bypass the factory boost cut, we went with Greddy's Boost Cut Controller (BCC).  This device caps the voltage signal coming from the manifold pressure sensor, so the car's computer will not invoke boost cut.  Since Greddy does not make a 2JZ-GTE specific BCC, you will need to source one for a 2nd generation MR2 (SW20 chassis).  Follow along as we show you how to install the BCC on a Lexus GS300/Toyota Aristo 2JZ-GTE VVT-i engine. 

As a precautionary note, if you are not comfortable with electronics or wiring, have a professional install the BCC for you.  We are not liable for any damage to you or your vehicle as a result of you working on your car or following our installation.

To start, we had to set the proper voltage cap for the BCC.  On VVT-i 2JZ-GTE motors like our JZS161 Aristo engine, the cap should be set to under 4.1V.  For those readers who have non-VVT-i motors, the cap is just under 4.3V.  We set ours to 4.08-4.09V.  To set the voltage cap, we removed the two philips screws on the side of the box (1 on each side).  With the screws removed, the box's shell can be removed to expose the internals. 
With the 2 screws removed, the BCC's cover can be removed to expose the adjustment screw (the upper left phillips head dial).

We adjusted the BCC to read just under 4.1V.
We took the red wire and the white wire, and attach them to the positive terminal of the battery.  Then we attached the black wire to the negative terminal of the battery.  The green wire was attached to the positive probe wire of our multimeter.  Turning the screw clockwise raised the voltage reading, and going counter clockwise lowered the voltage reading.

After properly adjusting the BCC, we reattached the outer casing, and then disconnected the car's battery to prevent any shorting out of wires during the installation.  On a JZS160/161 chassis car (1998-2005 Lexus GS300 and 1997-2005 Toyota Aristo), the computer is located behind the left side head light encased by a black plastic cover.  We had to remove 3 10mm bolts, and then a white plastic cover for the computer's plugs.  The white cover is easy to remove, just squeeze the main tab and pull it straight up.  Take care not to break the tab as it may be brittle from heat and age.

Next, we had to find a suitable spot to mount the BCC.  After a quick inspection, we decided to use the underside of the factory computer cover.  This would provide us with a stealthy installation.  We used some 3M double sided tape to mount the BCC.  Be sure to use a quality double sided tape.  Nothing is worse than having the device fall and get damaged from bouncing around.
We used 3M double sided tape to prepare our BCC for mounting.
Here is the BCC mounted to the inside of the computer cover.
With the BCC mounted, all that was left was the wiring!  A big thank you to Wilbo666 for providing the wiring schematics for anyone to use.  On our Lexus GS300, the wiring diagram matches an early model MK2 Toyota Aristo.  1998-2000 Lexus GS300 will be similar, if not the same as our car, but those of you with later model (2001+) GS300s will need to consult a wiring schematic.  We drew up a crude diagram of the wiring pins that we would need to use.
This is a quick note we wrote to assist us with the wiring of the BCC.

We sourced the BCC's red power wire to the F60 computer plug's IGSW pin.  The F60 plug is the plug that is closest to the front of the car.  We took a picture of the pin's wire to use, pin #9, the IGSW wire.  This wire will give a 12V signal when the keys are put to the "RUN" position.  The wire is a black wire with an orange stripe.
On the F60 plug, this is the pin for the wire we tapped for a 12V supply to the RED BCC wire.

This is the color of the wire to tap the BCC RED wire to.
The next wire we hooked up was the black ground wire.  We used plug B2, pin # 17.  The B2 plug is the 2nd plug that is closer to the rear of the car.  The ground wire is a brown wire with silver spots on it.
This is B2, pin # 17 for the BCC's ground wire to splice into.

This is the location of the wire if you're looking at the plug from head on.
Here's another look at the ground wire to tap into.

 The Green and White wires of the BCC had to be spliced into the manifold pressure sensor (MAP sensor).  That wire is on plug B2 as well, and it is pin # 9.  It is a green wire with a white stripe.  The wire needs to be cut, so be sure to leave plenty of wire on both sides of the cut to allow the BCC to connect easily without pulling on the harness.  A quick way to double check that this is the correct wire to cut is to check the MAP sensor on the intake manifold.  We looked at the middle wire of the MAP sensor, and it was indeed a green wire with a white stripe.
The MAP sensor wire is located in this pin where our probe end is pointing.
This is the MAP sensor wire.

This MAP sensor wire is green with a white stripe.  This wire needed to be cut.

On the intake manifold, the MAP sensor input wire is the middle wire, a green wire with a white stripe!  This checked out with the wire at the computer, so we were free to proceed.
We took the green BCC wire and connected it to the PLUG side of the wire.  The white BCC wire connected to the wiring that leads AWAY from the computer and to the MAP sensor.  We cannot stress this enough, but double check that you've connected these wires correctly as you do not want the computer to get the wrong signal. 

With the computer cover reinstalled, the BCC is completely hidden.  We love the stealth factor!

With the wiring complete, we plugged the harness back into the computer, put the white cover back over the plugs, and reinstalled the black plastic cover with the 3 10mm bolts.  Next, we reattached the battery to the car, and fired up the motor to make sure it ran properly.  With the BCC installed, we could surpass the factory boost cut, and we set our max boost pressure to 16 psi.  That is about the limit that the stock twin turbos and fuel injectors can handle with the pump gas available to us.  We might be able to turn it up to 17 psi, but we will see.  The ceramic turbine blades of the stock twin turbos are also not known for their strength at higher boost pressure, so we will need to get some larger fuel injectors and better turbos.  However, even at 16 psi, our car is no slouch.  Happy motoring and keep on driving!

Have any tech or automotive question?  Drop us a line at, or our Twitter.  We'd love to hear from you. 


  1. This is by far the best BCC write up instructions on the net!
    Great Work :D

    1. Thank you for the kind words! Glad to hear it's helpful.

  2. P.S to reference the pinout, got to;

  3. [IMG][/IMG]

  4. What would happen if the screw is turned all the way counter clockwise? Would this then lower the map voltage signal much too low, thus causing the ecu to adjust timing and air fuel ratios for a low boost scenario?

    1. Hi Brett, we don't have any direct experience with that scenario so we can't comment on what would happen. Our best guess is that you'll never hit boost cut, but your timing/fuel tables would be seriously affected due to the map voltage being way off.