The Mercedes Benz M103 engine is a 6 cyl engine and uses three teeth on the flywheel, each 60 degrees wide, leaving a 60 degree window between them. There is a single inductive/VR sensor of 830 Ohm to sense these teeth, the sensor wire has only one conductor with a shield.
After some discussion it has been revealed that the trigger input is not compatible with this type of signal. The input is a zero crossing detector, while this signal requires a level crossing detector.
Suggestions:
- The best bet is a very strong pullup to 5V
- Pull it to 1.0v or so and try a 10nF plastic cap for filtering. (Jörgen)
- There is place for cap (jp8 and jp7)
Right now the ECU has the "1k pulldown, lm1815pin5=5V" modification on the primary trigger input, which is not what I need.
The scope image below shows the signal picked up by the sensor while cranking at about 200 rpm.
The ground of the probe is connected to the shield of the sensor wire.
It is unknown which edge of each "tooth" is at TDC for each cylinder, but one of them is very close. On the 4 cyl Mercedes engines with this trigger the positive signal occurs at 55 deg BTDC and negative at 5 deg BTDC.
More on the engine here: http://en.wikipedia.org/wiki/Mercedes-Benz_M103_engine