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Paul - thanks for the detailed description of how the systems works, I think I understood it correctly before but probably missed a few things. I do know that the sensor is essentially a battery that outputs a DC voltage that depends on the concentration of oxygen. I always thought (and read) that if you monitor the voltage of the sensor (unpluggeed of course) and introduced false intack air (to simulate a lean condition) you should see a change in the output voltage. I did this test by opening the oil filler cap but maybe this doesn't really work on 911 engines.
With the sensor unplugged and the engine warm, the duty cycle (which is not really dwell) is dead on 50% which is what I think it's supposed to do.
It did occur to me that the system might be stuck in open loop mode but since I was able to see the dwell change when I grounded the o2 sensor input to the lambda computer, I assumed it was operating correctly (lambda computer basically ok and doing what it's suppose to do when it detects a low signal level on the input - reducing the dwell/duty cycle to compensate) It would be interesting to connect the sensor input to a low voltage source (1V or less) and see if the dwell goes the other way (as it should?)
Over my lunch hour, I pulled the o2 relay and took it apart (don't have a new one yet) I did check it carefully with an ohm meter and 12V supply and it appear to be functioning properly. Of course there's no load on the terminals so it could still have resistive contacts (clean them up a little with emery paper just for fun)
I'll check out the temperature switch on the right side of the engine. Assume this is the 15C switch and not the 35C switch? Where's the other (35C) switch located?
mike
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