Power ground

[Clarence Wood]

  I have a 1982 280ZX turbo with the Bosch L-Jetronic fuel injection.  I have been told that after modifying timing, etc. the battery ground should be disconnected for a period of time in order to reset the ECM.  I have also been told that both, negative and positive, terminals should be disconnected.  The time interval has been anywhere from 5 min to overnight.  Does the power ground,  as described below, explain why both terminals should be disconnected to reset the ECM??  Or am I reading to much into what is being said?  Could someone please tell me the correct way to reset the ECM?

At 12:14 PM 1/2/99 -0500, you wrote:
>Geoff Richards wrote:
>> 
>> Anyone have time to explain the difference between 'ground' and
>> 'powerground'?
>> TIA
>> Geoff
>I'll give it a crack.
>In a DC power system on a car, the negative(usually) terminal uses a
>"chassis ground" for power "return".This is your "power ground". It can
>have a voltage drop of up to .1 volt across it for accessory and
>charging loads, and up to one volt for starter loads.
>For signal circuits, such as sensors, sometimes the .1 volt drop across
>the frame ground could cause calibration errors, so a "signal ground" is
>provided. Sometimes the signal can even "float" above chassis ground, as
>through a protection diode with a, say, .6 volt forward voltage drop.
>Can't use chassis ground return for such a signal.
>Hope this helps understand it.
>
>