M70 runs only on 1 bank?

[shogun]

Copied from RF E31 board, refers to the M70 V12 engine, also used in E32 750:

Subject: I guess its my turn...Running on 6 cyllinders

Started it up. A little condensation smoke then awesome...
Left town for 6 days...Come home and start her right up..No problem. Drive her around town and get a coffee. Start her up...Only starts on 6! How do I know? Extremely sluggish and sputtering feeling. No major power. Drive it home (The long way) to look at it. No lights light up...No check engines or anything. One week later I ordered another DK motor from Wuffer because I thought that was it. Changed out both and still chugging and running on 6. No check engine lights either. Read through the archives... Mine is a 93 850ci with 126k
I changed plugs at 100k
fuel filters at 105k
air filter 1k ago
O2 sensors about 10k ago
new Dk motors
IM gaskets about 5k ago
reading through archives now...looking to find someone with a similiar problem. I am wondering about Spark plugs or wires....But so soon?


Answer by Mark:

Yes, it would. If plug lead 6 or 12 (the ones with the inductive pickup donuts on them) are disconnected or short, a protection circuit embedded within the Motronic will severely clip the duty cycle of the injectors for that side to protect the catalysts from being drenched in raw, unburned fuel.

Catalytic converter protection function
Ignition circuit monitoring

The ignition circuit is monitored by the cylinder detaction sender (pin 16) on ignition line 6 (or 12). If it detects no ignition signal on ignition line 6 (or 12) , the fuel supply to to the relevant cylinder bank is cut out by shortening the injection signal. The sender monitors the entire primary side of ignition, and cylinder 6 or 12 on the secondary side.
The inductive sensor is outlined in red above.

http://www.fibersonde.com/e31/images/engine/catprotect.jpg