Ground loops and 730 ECM

[Bruce Plecan]

> I am in the process of finishing my custom wiring harness to go
> between my 730 and the 1990 TPI (ZZ4) that I am installing into my
> Scout (of all things). Since I am using a fiberglass body, I have
> carefully created a ground bonding post (terminal strip)  on the
> firewall that everything should go to.  In fact the remote  battery's
> connect  there first.  so does all of the ECM connections. I have a
> heavy gauge wire connecting the motor to the bonding post also.
> unfortunately the fuel pumps and the alternator ground to the frame,
> but this doesn't really bother me since I am running a heavy gauge
> wire from the alternator to the bonding post also.
> There is one thing though that concerns me, its the O2 sensor (Bosch
> 12014)  circuit.  Pin E5 of the 1227730 is called out as the O2
> sensor ground.  I noticed that in the 730 it goes to some kind of Op
> amp that reads the sensor, but is in fact isolated from ground.
> so my question is how should I handle the 02 circuit? can I connect
> pin E5 to the ground bonding post (on my fiberglass firewall)  or
> should I run a line as close to the 02 sensor as possible?
> should I use a different 02 sensor? one that has an isolated ground?
> any ideas?

I'd first do it the way GM designed it, with the sensor grounds and ecm
grounds all tied together at the block.  Then the O2 is mute.
If you have to do it your way then there are 4 wire O2s used on the later GM
cars.   Vettes  come to mind.  I'd use a front one (all the 4 wires I know
of come with the pre and post O2 setup)(anyone hear / know different?)
Bruce


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