View Full Version : rough idle/no power -M70 - basics to check

11-16-2006, 11:17 PM

05-12-2009, 11:26 PM
In case 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 detection 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.


05-16-2009, 04:49 AM
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