GMECM Digest V2 #964

[Don Burns]

Hmmm... interesting difference in the results, which I suspect is due to
the differences in wiring of the two cars. I guess we will have to try it
both ways. It would be helpful to know the characteristic impedance of the
shielded line used. If you have any idea of this I'd like to hear it.

Len, did you ground the shield at the ECM end, and if yes, did you connect
the shield to the ECM housing or to the O2 input ground terminal? My
application is with a 730 ECM. As I recall, the schematic in the archives
shows a simple RC network at the O2 input of the ECM. Do you have any idea
what the R and C values are?

Don


Joe said...

>I've had good luck with braided shielding in other applications
>(specifically, fire and gas detection systems), but it is very critical NOT
>to ground both ends.  The shield needs to be grounded on one end and the
>other protected by heat shrink or any method to prevent it from creating
>another ground path.  What happens is the creation of an antenna.  I missed
>putting heat shrink on one end of a cable and only a few wires from the
>braid touched the conduit.  When a portable radio was brought into the
>vicinity and keyed - the system tripped.  It turns out that no shield is
>better than one grounded on both ends (in my experience anyway).
>
>Joe


Len said...

>>      Braided ground shield seems to work best , both ends grounded.
>>      It does help remove any Rf garbage from the signal .
>>      A Scope will show how much trash is present in the general area.
>>     There's filtering built into the ECM for this purpose as well.
>>      Len
>>
>> >I posted this a week or so ago but apparently the server was down so here
>> >it is again.
>> >
>> >Many months back some posted a comment to gmecm about shielding their O2
>> >sensor wire to eliminate a problem with ignition noise. If you are still
>> >around I'd like to hear more about what you did. Shielded cable
>impedance?
>> >Length? How the shield is grounded, one end or both ends?


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