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.
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