I have this engine in my '81 euro E24 build date 5/81
First of all, Realoem does not show that part number when I search under an '81 euro E24. The
81 M90 is a Motronic injected motor. As with all Motronic motors, it will have a front mounted dizzy. If side mounted, the engine has been bastardized.
The Motronic injected M90 was only of one year production. It was the last year of the M90 and unlike the early M90 Motors, it does not have the raised water passage on the left side of the block, uses a 1 year only wiring harness and also runs low impedence injectors, and of course Motronic basic injection.The correct ECU is an 002. Again, only available for 1 year of production. An original to the car motor will also have the original VIN stamped above the starter on a flat on the block
Many people told me this couldn't be a factory original setup, so I started doing my research, I ran into a fellow in OZ named Remy Davis. He is the one who "enlightened
me" to most of the correct information. After finding at least 20 cars the same on various E24 boards, I contacted Andreas Haartz of Mobil Traditions in Germany who verified to me that it was a totally correct motor and of original production from 5/81- 5/82 on at least the E24s