Hex is base a 16 numbering system. Instead of digits from 0 to 9, hex uses digits from 0 to F. So A = 10, B = 11, ... F = 15. Typically we distinguish hex numbers from other numbers by either putting 0x at the front of the number or putting an 'h' at the end. i.e. 0xFE and FEh are both the hex number FE.

So, you've found the fuel and timing tables in your ECU's program, edit away. Most ECUs have a Check Sum routine - the checksum gods must be appeased after any changes to the ROM are made or the car will not run properly. It would take a long time to tune a car if everyone only had hexeditors at their disposal. In many cases, ROM editors are available to assist in the tuning process.

So, you've found the fuel and timing tables in your ECU's program, edit away. How do you interpret all this? Well, first you mut know about the addresses. Each byte has its own address referenced by the left most column (the "offset" column) and the top row. As an example, look to the bottom right corner of the above picture. Notice the byte that has 6f as its value. Follow the row to the corresponding row in the offset column and you will see a 3ef0. Then follow 6f's column all the way up to the F on the top row. Put those values together and you have the address of the 6f byte: 0x3eff.

Now what? This data is the binary representation of the actual machine code that runs in the ecu's processor and ROM data that the ECU uses. To figure out what it does you must use a disassembler to convert the binary code/data into the machine code instructions which are more human readable.

Most ECUs have a Check Sum routine - the checksum gods must be appeased after any changes to the ROM are made or the car will not run properly. It would take a long time to tune a car if everyone only had hexeditors at their disposal. In many cases, ROM editors are available to assist in the tuning process.

If you have a OBD2 ECU, you are just going to have to wait or buy commercial Tech Tom gear. It is possible to remove the 66K MCU and replace it with another OTP 66P507 or FLASH 66Q589 (As the case may be) but this is far from trivial. Little is known about OBD2 code.

If you have a OBD2 ECU, you are just going to have to wait or buy commercial Tech Tom gear. It is possible to remove the 66K MCU and replace it with another OTP 66P507 or FLASH 66Q589 (As the case may be) but this is far from trivial. Little is known about OBD2 code. See Chipping OBD2 by Doc