RX8Club.com - Series I Engine Tuning Forum https://www.rx8club.com/ EMS (Flash Tuning, Interceptor, Piggy Back, Stand Alone) en Tue, 19 May 2026 09:42:58 GMT vBulletin 60 https://www.rx8club.com/images/misc/rss.jpg RX8Club.com - Series I Engine Tuning Forum https://www.rx8club.com/ <![CDATA[Open Source Stock ECU G-ROM FlexFuel ROM - User's Guide]]> https://www.rx8club.com/series-i-engine-tuning-forum-63/open-source-stock-ecu-g-rom-flexfuel-rom-users-guide-276788/ Fri, 08 May 2026 19:01:55 GMT Hello friends, I figured it was finally time to document some of this stuff in an easy to intake format that wasn't totally spread across 4 different platforms.

The information in this thread will describe how to use my FlexFuel patched factory software and explain what this software does on TOP of the already existing open source ECU information. Most of the terms and tools will be identical to the open source stuff I have posted before, so if you need some context or are just seeing this post first, I would HIGHLY encourage you to read through the existing thread on that here:

https://www.rx8club.com/series-i-eng...-guide-276137/

ROM Features
  • 0-100% Ethanol content fueling, no fuel re-mapping required if not desired
  • Immobilizer Removal
  • Additional engine timing scaled as a factor of ethanol content
  • Cranking fueling scaled as a factor of ethanol content (base calibrations available)
  • Extra parameter PIDs for more informative logging via OBD
Supported ECUs
  • 04-07 USDM 6 Port 6 Speed ECUs
ROM Bases
  • 60E0FB00
    • N3Z2ET 2004 US 6 Port MT
  • 60E0FC00
    • N3Z2EU 2004 US 6 Port MT
**NOTE: 4 Port and Automatic ECUs/Calibrations will never be supported without SIGNIFICANT effort

First and foremost, I think it's appropriate to acknowledge a few gaps in knowledge I have as far as ECU support: I believe you can straight flash the G-ROM FlexFuel ROM on to any USDM S1 6 port ECU, but I have not investigated the use of any other ECU ID and do not totally understand the hardware differences. I am happy to work through issues with people to bridge this information gap! Super worse case, we can work with your base ROM and port the patch over.

Tools RequiredOptional Tools for Advanced Users
  • G-ROM Patcher - Utility for patching software modifications on top of an existing OEM ROM

Additional Vehicle Requirements
  • A FlexFuel sensor that outputs the ethanol content to CAN in the G-ROM FlexFuel format (I do build and sell these CAN adapters boards which can be found here: https://g-rom-electronics.myshopify....nsor-converter)
  • Stock fuel pump, fuel lines and injectors will be adequate for most installs
Benefits of E85 on an RX8
  • Mo powah! People (including myself using this ROM) have seen 20whp pickups, which is a 10% power increase
Open Source Bits
Software for this patch was written in a combination of ASM and C code, using a compiler made for the Rensas microcontroller on the ECU. The vast majority of effort goes into the linker, and what functions to use as a way to run the additional software.

The source code and build environment for you to look over, as well as modify freely can be found here: https://github.com/equinox311/RX8_FlexFuel

I can dive into ways in which you can write your own software for the Mazda ECU if there is interest, but this isn't entirely the thread for it. I will go through the software and it's functionality for the FlexFuel related additions.

Okay into the fun bits!!

Installing a FlexFuel Sensor
This assumes the use of a GM/Continental ethanol sensor, and all information on install for a G-ROM Converter into the factory RX-8 CAN bus can be found here: https://gromelectronics.net/wp-conte...r-manual-1.pdf
The sensor is required to send ethanol content over CAN to the ECM in the format as specified in that document.

You can refer to many other guides for more information regarding the sensor install and wiring, but I do recommend that the sensor is installed in the fuel line that goes DIRECTLY to the fuel rail. This should not be a problem on a stock fuel system RX-8

G-ROM Flex Fuel Calibration Tables
Download the latest released version of the ROM as shown above, and open it in ROMraider ECU editor (if you need to figure out how to do this, please refer to the base Open Source thread from above).

When you open the ROM up, you should see a list of tables populated in ROMraider much like a factory RX-8 ROM, and the calibration ID in the header should show up as "G_ROM_FLEX".

You should also notice the additional category of calibrations labeled "Flex Fuel"



Table Definitions and Functions

Stoich Fuel Ratio Table

This table sets the stoichometric ratio of air to fuel for a given ethanol content. This table is already setup to be accurate, and shouldn't ever need modification but it is present in the definitions in case someone wants to play. This value is what sets the base AFR for the software to properly inject fuel in all cases. There is no need for any additional closed loop or open loop fueling as this value is what sets the math up correct for the ECU to use the standard lambda tables. If there is desire to lean/enrich fueling targets based on ethanol content, please send me a message and this functionality can be added.



Ethanol Sensor CAN ID

This is a raw integer value for the received CAN message ID for the software to receive ethanol content on. If you don't know what that sentence meant, it's very unlikely you will need to change this.



Ethanol Content Sample Thresholds (Engine Speed and Engine Load)

These tables are thresholds for which, when the engine speed or engine load are greater than, the ethanol content as read in from the sensor will not update and not effect fueling. This is a method in which to filter out noisy data in high fuel flow situations, and is very similar to the Haltech strategy. Out of the box, they are set to values such that the feature is effectively turned off.



Cranking Fuel Multiplier

This table is a fueling multiplier meant to add additional cranking fuel during cold starts to help with flame propagation at lower temperatures. The value from this table is a multiplier to the OEM Primary Fuel Injector Cranking Pulse Width (see cranking pulse calculation below). Out of the box the multiplier is set to 1, such that factory cranking fueling will be used in all conditions. The table is based on current ethanol content and engine coolant temperature. The software will protect against a value of anything less than 1.0 being put into this table, but if someone really feels the need to lower is, please send me a message.



Flex Fuel related cranking fuel calculation is as such:

flex_fuel_injector_pulse_cranking = primary_fuel_injector_pulse_cranking * cranking_fuel_mult

Timing Ethanol Adder - Leading/Trailing

These tables set the amount of additional timing added to the base timing calculation and are effected by the Timing Multiplier (See timing calculation below). These tables should be tuned such that the timing value set in the table, is the maximum added to the base timing at your maximum desired ethanol content. The tables exist for the leading and trailing sides. Out of the box they are set to 0.



Timing Multiplier

This table sets the timing adder multiplier based on the ethanol content percentage. This is to say that the amount of timing in the Timing Ethanol Adder tables is multiplied by this value to come up with the actual amount of timing added to the base timing from the factory software (See timing calculation below).



Flex Fuel related timing calculation is as such:

timing_adder_trailing = timing_ethanol_adder_trailing * timing_mult

timing_adder_leading = timing_ethanol_adder_leading * timing_mult

Flashing the G-ROM FlexFuel ROM to your ECU

Download the latest released version of the ROM as shown above from the Current_Release folder on github, make your calibration tweaks using RX8Man Software, and flash it as tuned and described in the open source information thread, and you're ready to go!

Logging and Debug
To log parameters and confirm that you are up and running with software, you should use ROMraider logger and the most up to date logger definitions. For instructions on how to set this up, refer to the existing open source thread as the process is the same.

It is also worth noting that with a basic Versatuner/Mazdaedit/etc logging license, you SHOULD be able to use those programs to log basic parameters. I will not gaurentee this, and you cannot be using their software on the ECM. Programs like FORscan can still log parameters exactly as an OEM ECU would.

With ROMraider logger open, if you connect to the ECM, you should see some metrics pop up on the left side that are additional to the stock ROM.

Flex Fuel Logging Parameters

These should be self explanatory, but I will explain them simply:
  • Ethanol Content - This is the current ethanol content as read by the flex fuel sensor over CAN
  • Flex Cranking Multiplier - This is the current cranking multiplier applied from the Cranking Fuel Multiplier table above
  • Flex Fuel Timing Muliplier - This is the timing multiplier as applied from the Timing Multiplier table above
  • Flex Leading Ignition Timing Adder - This is the current added timing to the base timing as calculated from the timing calculation above for the leading spark plug
  • Flex Trailing Ignition Timing Adder - This is the current added timing to the base timing as calculated from the timing calculation above for the trailing spark plug
  • Flex Sensor Fault Status - This is a validity bit which tells you if the ECM is reading the ethanol content CAN message correctly. A value of 0 denotes there is no problem, a value of 1 denotes the ECM has not received the ethanol content CAN message within it's expected transmit period (NOTE: The Ethanol Content should also default to 15% when this value is set to 1)



Additional Logging Parameters (experimental and more to come)
  • Air Fuel Ratio - This is the current air/fuel ratio in Lambda/AFR Gasoline/AFR Ethanol that the ECM is using for it's fueling
  • OL Fuel Final - This is the current request lambda/enrichment value that the open loop fueling software is requesting

]]> Series I Engine Tuning Forum equinox92 https://www.rx8club.com/series-i-engine-tuning-forum-63/open-source-stock-ecu-g-rom-flexfuel-rom-users-guide-276788/ Tactrix Openport 2.0 Cable Replacement https://www.rx8club.com/series-i-engine-tuning-forum-63/tactrix-openport-2-0-cable-replacement-276782/ Mon, 04 May 2026 02:06:21 GMT Hello All,

I've recently purchased MazdaEdit and an OBDXPro VX cable since Tactrix Openport 2.0 cable is no longer available and it was mentioned on the MazdaEdit website to be a supported cable. I ran into issues with downloading my OEM ECU file and reached out to both MazdaEdit and OBDXPro. They both confirmed that the OBDXPro VX cable does not work with the RX-8. OBDXPro said that they have found the communication line from the RX-8 to be noisy which causes communication issues. They also said they are working on a product for this but are several months out from releasing anything.

With all of that being said, does anyone know of any sort of replacement for the Tactrix Openport 2.0 cable?

]]> Series I Engine Tuning Forum spartans55 https://www.rx8club.com/series-i-engine-tuning-forum-63/tactrix-openport-2-0-cable-replacement-276782/