MSD87. Management of the ignition coils

This time – let’s see, have the BMW engineers noticed and prevented the main reason, why the ignition coils of N43/N53 and coil management switches of MSD80 management units so often go out of order. Yes, MSD81 and MSD87 have more powerful switches with overvoltage protection – their failure is rarer, but, for example, for MSD81 the problems with a short serving time of the ignition coils were not less (so – replacement of the switches didn’t solve the cause of the problem).


I connected the oscilloscope to the ignition coil of the MSD87 (F10/N53):

Wonderful – no changes since MSD80/81! Max voltage reaches around 320V, which exactly corresponds to the threshold of protection of the switch. Reaching this voltage, the power switch tries to “protect” itself – it tries to open. As a result, the waving of the signal, visible in the image, starts (more detailed description in an entry regarding MSD80 – here).
There is no doubt – the ignition coils are eternal headaches of the F series vehicle owners. Solution? Installing the snubbers.
Besides, the voltage growing speed Trise is significant (it is not limited): around 50 .. 80V/us, which guarantees a high level of interference in while the electrical system of the car and gives a risk to damage the insulation of the wiring (for E series such problems were sometimes observed).