BMW M70 Tuning Tips - Remapping?

[E31Ron]

I was reading your page at https://www.torquecars.com/bmw/m70-tuning.php

Great web page, lots of useful information!

In it, you say: "Remaps should help to unlock the full potential of all the mods you've done to your M70. (In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)"

Can you explain what is meant by "the factory ECU is locked"?

On the M70 engine, the ECUs have replaceable chips, for which many aftermarket versions are available as plug-in replacements, so flashing and locking are not issues.

But on the M73 successor engine to the M70, built for OBDII, the ECUs have EEPROMs, about which I have heard the term "locked." People say you will brick them if you try to flash them. I have also heard of tuners who are able to work around this, but have never actually been able to find one.

Can you explain any more about how this works, and why those ECUs cannot be flashed?

Or refer me to any links that discuss this further?

Thank you,

-- E31Ron-

 

[obi_waynne]

To oversimplify a complex subject the ECU's contain checksums, a number generated say every 500 lines of code and relates to the content of the previous code. It can be a simple as keeping it odd and even, or it can be an average of all the values, a MD5 type generated code or something unique. The outcome is that if you change the contents of the file and don't have a matching checksum it will reject the block of data completely. When manufacturers use common ECUs like Bosch Motronic or Siemens there are formulas that generate the checksums. When uncommon ECUs are used, or manufacturers create their own "check codes" or "checksums" flashing becomes impossible as all new code is rejected. [For example my checksum for this paragraph is 122697 (122 words and 697 characters, so if anyone changed a word it would fail the checksum as the values will not match. ECU checksums are more complex than this. ]

Replacing chips is often an option, and bench flashing where the chip is directly flashed and the code doesn't pass through the OBDII gatekeeper can often be done. This is where the chip is connected to the flasher directly.

On some BMW's there is a Bootmod3 option, which allows you to alter ECU code. There are also plug in boxes which become a secondary ECU.

Sorry for my slow reply, I've been pretty poorly the last 3 weeks and am just catching up.

 

[E31Ron]

Thanks for the comprehensive answer, and explanation.

Do you, or anyone else here, have any specific information about the M73 ECUs (DME, EML, EGS) installed on the BMW limited production 1995-1999 E31 850 M73 engines?

I have also read that the later version of the same engine, the M73TU installed in the E38 1999-2001 750i does not suffer from the same blocks to reprogramming (and so offer a possible route to E31 modding via a transplant of all 4 boxes).

Thank you for any perspective,

-- Ron