m20b25 ECU : do I have the "good" one ?

[stratos92]

Hi all,

I have some questions about 325i E30 ECU with / without catalystic convertor.

My car is a french 2 door 325i, from december 1987.
It is 100% stock (except Hartge 16 rims and 70.000km BMW engine) and do not have (it did not even exist in France at this time) any lambda and catalytic convertor, so it is a "171hp", not the "170hp" and its low compression ratio.

Some years ago, I purchased to a german Ebayer (Xtreme technology, no longer selling chips on Ebay) a "performance" chip (giving him my ECU number, which is : 0 261 200 380, yellow label).

I recently found the time to mount the chip, but did this on another ECU (0 261 200 380 yellow label too), coming from Ebay Germany too (my purpose was : to "swap" more easily and quickier between stock and modifed ECUs, without removing the fragile chips, and to let the "original" ECU unopened).

Having some idle (a bit too high) and low rpm issues (like 1/10 sec stall when switching gears, especially 1 to 2) with this chip (but the power gain is realy noticeable!) after a short drive (+/- 150km) , I suddenly asked to myself about the ECU version.

Since there is a VIN on every ECU, I made an internet research, leading to :

- my own car VIN : well registered as "without catalyst" (ok! this was just for checking the website database reliability)
- my "original" ECU VIN, fitted on my vehicule : resistred as "with catalyst" (?!??) (convertible)
- the german Ebay ECU VIN : registred as "with catalyst" too ! (touring)

So, I felt surprised to discover that the ECU fitted on my car (I purchased it in 1999) was not the original one (different VIN numbers) and seems to be designed for "catalyst". But it sill worked flawless anytime.

Now, I wonder if :
For a same ECU Motronic number (in may case : "380"), are the ECU the same (except the chip inside), between catalyst and no catalyst engines ?
Is the software difference between catalyst/no catalyst located only in the chip (this would be great), or are there other differences eslewhere in the ECU ? (if so, I should look after a french ECU...)

I am a bit confused, wondering if running a "catalyst" ECU on a "non catalsyt" car would have any downside effects (I mean especialy reliability, pinging...)

Thank you for your help.

[Speedtouch]

Welcome to the Zone!

You are best off with the 0 261 200 173 ECU - the later 380 version (which, incidentally, is strange to have on a late 1987 car - they were normally fitted to 1992-on ones, in the UK at least) had extra diodes in the idle control circuit, which are prone to blowing, which may be why your second 380 one gave issues.

AFAIK, yes, the ECUs will be identical hardware-wise apart from the program on the EPROM chip, which may have revisions depending on whether or not a catalytic converter was fitted.

[stratos92]

Thank you very much Speedtouch !

Yes, after posting my question, I recently discovered that my low rpm and idle issues did realy come from the second ECU : it appeared to be defective, and your answer confirm this : I could check it by puting back its own original software on it, instead of the "Xtreme" chip, and it had exactly the same issues ! So I don't ever use it....I think it can now work as an ECU for...a dustbin only

I prefer to keep on with my "original" unit (working fine) or, as you suggest, another one, but 173.

I guess my car came out from factory on dec. 1987 with a "173" unit, and, for a reason I can not know, a previous owner put later a "380" on it, maybe for the supposed better start and iddle management...I know that the second owner was a BMW mechanic, this could be an explanation.

[Speedtouch]

Could well be. Your second 380 ECU may be repairable - diodes only cost a few pence, and are easily replaced if you're handy with a soldering iron.

[stratos92]

Goo idea, since I can handle a soldering iron with no problem...I just need to know the references and location of the diodes...it would indeed be good to have a "spare" working ECU..I paid about 150 euro when I purchased it on Ebay.de some years ago !