Hi,

I was at Donnington yesterday, and I was told by the BMW breaker in London (Harrow, Zack I think his name is) that some cars have a double ECU, and that they are very hard to come by, and very few cars had them fitted.

This is in fact totaly untrue. Under the drivers (RHD cars) footwell, once the under-cladding of the dashboard has been taken off, the ECU's are located on the offside.

Well my 1985 635 has 2 of them, both mounted together, one with a black label, and one with a red label with 'MOTRONIC' stamped into its metal cover. Both are Bosch units, and both have metal housings.

It turns out that the one with the black label is the control box for the switchable auto gearbox control, while the one with the red label is the Motronic ECU.

Thus, there is only one ECU after all. This setup featured from the late '84/ early '85 cars up until the end of the chrome bumper e24's, and the introduction of the Highline - when of course the engine and fuel injection is different. The same applies to pre '84 cars, where once again there are differences. Also, cars without the switchable auto clearly don't have the box with the black label.

Problem solved. Incedently RealOEM does not list the part numbers for these Bosch units for some reason.

In addition, the box under the bonnet on the nearside of the pannel that covers the blower motor is the ABS control box.

I hope this helps some of you out - now... if I could only get my car to start.

-Ben

I think there is another box under the dashboard on the drivers side under the steering wheel as when i broke my spares 635 i found a box there. This was the one that went wrong on my six 5 years ago. There is also a unit behind the dash on the other side and one under the blower cover. Thats for a manual six. I don't know what each box does, but ZAC generally knows his stuff although i thought he had sold his business.

James

    Switchable auto 635s from 83 /84 had the 'double' ecu , later cars had a seperate ecu for engine and gearbox. This is what Zac said and meant. The part number for the 'double 'ecu usually ends in 018 and the later seperate engine ecu ends in  061. Both ecus are troublesome ,and being an e23/24 fiend i have good used ones in stock.

Sohlman wrote: ....but ZAC generally knows his stuff although i thought he had sold his business.

Still going strong from what I saw yesterday. Yours and Brian Jordan's little "clearout" merely allowed Zack more space to get more parts in

Hiabboy wrote:    Switchable auto 635s from 83 /84 had the 'double' ecu , later cars had a seperate ecu for engine and gearbox. This is what Zac said and meant. The part number for the 'double 'ecu usually ends in 018 and the later seperate engine ecu ends in  061. Both ecus are troublesome ,and being an e23/24 fiend i have good used ones in stock.

Since Ben has now acquired the gearbox "box", he will now need to test the other "Motronic"-stamped box.

"Hiabboy", over to you.....

thats right it does have the 2 separates, weith those part no's - but I was told the wrong thing - but its sorted now thanks.

The red 061 is correct and what mine has

Ben

   Ben has just been around and we tried his ecu and fortunately/ unfortunately the 535 turd started and ran fine ,so it is not the ecu.

        I have given him an obc box (the one with 2 green 4 pin plugs) to try but his tale of alarm woes sounds a bit ominous !