Running on 6 cylinders only? M70 engine

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   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

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shogun Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Really Senior Member II Joined: 22-February-2005 Location: Tokyo/Japan Status: Offline Points: 564	Post Options Post Reply Quote shogun Report Post Thanks(0) Quote Reply Topic: Running on 6 cylinders only? M70 engine Posted: 13-May-2009 at 13:13
	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
	E32 750iL,E36 M3 7 Series Tech Tips

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shogun Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Really Senior Member II Joined: 22-February-2005 Location: Tokyo/Japan Status: Offline Points: 564	Post Options Post Reply Quote shogun Report Post Thanks(0) Quote Reply Posted: 16-May-2009 at 11:30
	The above was from roadfly E31 board, and the MOTRONIC was 1.7 M70. Now we just tried: results of test (simple) Shogun's 1988/89 750iL (11/88, MOTRONIC version 1.2) well we disconnected the passenger side cylinder ID plug at front of engine. key to position 2, EML light comes on, after a few seconds off. engine start, runs on only 6 cylinders and rough -- NO EML or other warning! Accelerator used, still no warning. Reconnected and restart -- all 12 running, no warning. Disconnected both cylinder ID plugs. same result -- engine runs but only 6. Used Peake Fault Code reader and found no fault codes related to engine --ummm Reconnected and runs like a champ. Still no warnings. I thought the engine would stop with both disconnected but no true. Over to you guys
	E32 750iL,E36 M3 7 Series Tech Tips