At 1:13 PM -0400 4/14/00, Frank Grunthaner wrote:
>
>Anyway, when I did my conversion (many years ago, diesel to gas). I placed
>the ground wire from the Digifant system that is supposed to go to the head
>to the body instead. Ground is ground I said! Well, triggered by recent posts
>by Ken Lewis over my starter saga, I rigged up a switched system to go back
>and forth (ignition off!) between the body ground and the head ground. I saw
>on the oscilloscope (250 MHz bandwidth) an amazing change in the fuel
>injector waveform, and in the O2 sensor waveform. The fuel injector pulses
>were shorter and sharper (faster rise and fall times) and the same was
>observed for the O2 signal. The integrated or mean voltage of the O2 signal
>was also different by 0.072 volts indicating a leaner running condition.

Aside form the AC effects of noise and inductance on the "antenna"
path of your ground between the engine and the body, there is a major
voltage drop from the engine to the body caused by the alternator
current which is returning through that ground connection. You can
observe this drop with a just a voltmeter (millivolt range, I hope
;-) and watch it change. It will be large if your battery is taking a
charge and will vary with loads such as lights and heater fans. As I
understand it, the O2 sensor is the most sensitive item since it
likes to run at 0.5V and is grounded to the exhaust system. An offset
of .2 volts (not uncommon in my experience) would make significant
changes to your mixture.

HTH

  -Otmar-
82/86 Stretch Vanagon Westfalia Syncro GTI. "Power of two"
http://www.evcl.com/vw
Several EVs (Electric Vehicles)