DME Remapping
 

Just was reading about DME Remapping, and actually did not even know that a "spirited" drive should follow having the battery disconnected for any period of time over 20 min. The last time I had my battery disconnected I had the alternator out replacing a fan bearing. After replacing the bearing and connecting the battery I took it for a nice slow drive b/c the engine was cold and didn’t want to drive it too hard until I made sure I didn’t make any mistakes. SO my question is should I get my engine warm disconnect the battery wait 25 min and drive the snot out of it. Will this change the performance? The spirited drive following a battery disconnect vs. a slow drive?

Thanks,
Ryan

It is always remapping itself. The quick way to do it is the few minutes at idle then a "spirited" drive.

and with the engine "pre-heated"....
I don't think you need to disconnect the batt for longer than a couple of minutes or.
I've seen some say 20 minutes but I have never heard any reason for that (i.e. something that needs to drain a charge?)

Now I'll bet someone will post one :)

I've often wondered about this, and have even asked here without any definitive response. I expected that the remapping would be a constant process. Is this documented anywhere? Not that I doubt you! Just curious.

Cheers,
Dave

The PO of my car had a collection of 12 or so nice cars and had a quick disconnect on the battery b/c he only drove it every couple of weeks. He was very persistent when i bought it that i not drive it too hard before it was warmed up...just makes me wonder about the DME mapping.

From what I have read... The "spirited drive' is to get the DME back up to snuff as quickly as possible. It is always in a learning mode... It just learns more quickly after you run the snot out of it. If you drive slowly it will just take longer to learn.

As far as leaving it disconnected... I have always assumed that there are capacitors that need to drain their charge. I've always heard that you should disconnect it for at least 30 minutes. I'm sure someone will chime in with the straight dope.

Sorry dont mean to hijack the thread but this is related to the above question.

My car recently had its chip replaced and was remapped on a rolling road. So does my car still constantly update itsellf? will a DMA reset or Hammer Adaption still do something?

The remapping is a constant process intended to keep the engine controls consistent with the season, and the weather. I am not sure about newer Porsches, but the new BMWs even adapt the engine controls to your driving style (economy or sport usage).

The only purpose for the spirited drive is to ensure the DME sees the full range of engine output as soon as possible. For example, if you never wind out to the redline, the DME will have no data (the map) for setting the timing in the upper RPM range. Is that a problem? Only the first couple of times you pull out to pass someone and find you are missing a few HP.

Just for clarification,

If you have an aftermarket chip, does the DME reset do anything for you?

And on that same note, will a Hammer idle adaptation do anything for an aftermarket equipped DME?

i.e. do the aftermarket chips still have the "learning" function

The 964 DME does NOT remap itself. The only "adaptation" it has is the idle CO
adaptation which corresponds to the TRA function, i.e. O2 range correction for
small variable changes, e.g. intake air leak, in the OBDII DMEs used in the 993s
and later Porsches AND idle speed adaptation (static & NOT dynamic - LWF mod).

Wow, this confuses my fragile brain.

Why do numerous publications call for a "spirited drive" after a battery disconnect? I would guess this doesn't have anything to do with idle.
So why!? why!!!? WHY!??!! I must know.... :)

Mark,

I'm afraid the "spirited drive" claim is a myth. If you would like to see what's happening inside the Motronic ECU I suggest you look into the free diagnostic software that's been discussed in this forum.

The software will actually show you how the DME "adapts" the fuel mixture. There are low range and high range "trim" values that are derived from how much the DME has had to adjust the fuel quantity to achieve the proper air/fuel ratio. These "trim" values are adjusted periodically but usually don't change much unless you have an intake leak or you drive up a really tall mountain--the DME cares not and knows not how you drive. The "trims" are stored in 2 BYTES (!) of battery-backed memory so they are ready to come into play the next time you start the car.

There's also something called 'system adaptation' that is performed using the diagnostic scanner. 'System adaptation' simply causes the DME to store 1 byte of data relating to the idle air valve position into battery backed memory.

I should add that the amount of stuff stored on the 964's EPROM takes up fewer bytes than a typical rennlist thread!

Also, don't let anybody knock the 964 Motronic. It provides sequential injection and cylinder selective knock control--which is very,very cool.

-doug

Thanks Doug! Sounds definitive. Just 2 bytes of data?! That's funny.

Surprising that the "adaptive" myth is perpetuated in Adrian's book (p134, 184) along with various forums, etc.

I appreciate the clarity of your post. Makes sense.

Thanks doug,

If I understand you correctly even though my car has been remapped and had a different chip its still worth while doing an adaption every now and again as well?

Same stuff applies to aftermarket chips.

Are you referring to the 'system adaptation' thing that is performed with the diagnostic scanner? I bet a lot of cars have never had this done and they're running just fine. I've heard that it has helped some cars with idle problems though. Has only a slight effect on my car so I never bother.

-doug