My Automotive FAQ - G-Force ECU Upgrade - why you need/want one.

Let me be very clear.  I feel strongly that the G-Force ECU upgrade should be one of the first modifications made to a Celica All-Trac or MR2 with the turbocharged 2.0L 3S-GTE.

Background.  The factory ecu in the All-Trac provides fuel and timing maps up to 12 psi of boost.  However, when performance-junkies start increasing the power of turbocharged cars, one of the first modifications is an increase of boost pressure.  When the factory ecu detects a boost level at or above 12 psi, the ecu enters "self-preservation mode" and begins taking countermeasures to prevent destruction of the engine.   One such countermeasure is to cut fuel to the engine by not firing the injectors.  

Overview.   I like the G-force upgrade. Yes, it's not inexpensive, but it eliminates the various band-aids and hacks that are otherwise used to make more power on the turbo 3S-GTE.  G-Force piggybacks a chip on to your ECU that takes over all the  functions the ECU controls.

G-Force's "default" upgrade, includes disabling the 12 psi fuel-cut, providing proper fueling and ignition for up to 16 psi, and increasing the rev limiter to near 7500-7800 rpms.  

So with the G-Force modification, you don't need the HKS FCD or the zener-diode mod.  Additionally, your engine will receive correct fueling at boost pressures above 12 psi, since the stock ecu programming is limited to the 12 psi fuel map.

Although these are the basic modifications, you may request additional changes to ignition timing, the fuel curve, or an even higher or eliminated rev limit.  These additional mods can be requested at the time the
ECU is initially modified, or sometime later in the future. If done in the future, you can get these changes on a singe chip for $150.  

Pros.  The G-Force modification...
>  programs in new fuel and ignition maps which optimize the performance of the 3SGTE. Toyota programs their ECU's to run  rich to guard against warranty claims. G-force programs their ECU's to  boost performance. 
>  eliminates fuel-cut from occurring at boost levels of 12 psi and above, and this subsequently eliminates the need for a HKS Fuel Cut Defencer and the zener-diode mod.
>  supplies the correct amount of fuel so a Fuel Pressure Riser is  not needed unless you need more fuel than the stock pump can provide. 
>  optimizes the ignition so you don't need control over timing or rev  limiter but you should consider a high output coil and high quality wires.
>  optimizes the air/fuel ratio so you don't need a HKS VPC.  That said, a VPC provides other benefits in that it converts the air metering from an AFM to  a MAP sensor.  The G-Force is usable with a VPC, as I ran this combination for an entire year.
>  allows fuel and timing maps up to 16 psi.
>  allows a higher rev-limit.

Nearly everyone with a G-Force ecu will tell you that it has made a noticeable difference in performance on their individual car.  Although I cannot confirm, it has been reported that the G-Force ecu mod is worth about 25 hp.

Cons.   The G-Force modification...
>  is expensive.  At $700 USD, this mod is not cheap!
>  is not dyno-tuned for your individual engine in the manner that an aftermarket EMS is tunable for a specific set of modifications.  That said, G-force will reprogram your G-force ECU for around $150 to take into account future modifications you make to your car.
>  still uses  the stock AFM, which is a restrictive passageway through which the incoming air-charge must pass before entering the turbo.  If and when the AFM fails, you must replace it, and rumor has it that the AFM is expensive.
>  cannot accurately meter fuel with 550 cc/min injectors.  Many months ago, G-Force indicated they were working on a new ecu program to support 550 cc/min injectors, but they have given up on this development effort.  In fact, they recommended I get a new chip for my HKS VPC from Toyomoto in Florida.  Unfortunately, this option is unavailable to you unless you are using an HKS VPC on your All-Trac or MR2.

Summary.   IMHO, the G-Force upgrade is good for anyone that wants to safely make more power from your 3S-GTE.  However, there is a point where the G-Force will yield to an aftermarket EMS such as my Autronic SMC system.  That said, I feel most All-Tracs built for street duty will live quite happily with the G-Force ecu.

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