[V8] ECU grounding, etc. - Check engine light

[Tony and Lillie]

----- Original Message ----- 
From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
To: <v8 at audifans.com>
Sent: Tuesday, October 11, 2005 3:43 PM
Subject: Re: [V8] ECU grounding, etc. (abridged)


> ... while I've found the wiring diagram to be pretty much literally
> correct in its description of the connections and how they are made you
> may well want to be a bit skeptical.  The wiring diagram may show a
> direct wire connecting two points, when the connection may be a bit more
> indirect.
>
> We've had the discussion here in the past ... proper grounding can be a
> very tricky thing ... it is better to keep the grounds for sensors
> separate for grounds for things that the ECU drives ... but then ground
> needs to be connected together somewhere.  The example I always come
> back to is the two grounding lugs that attach to the back of the engine
> below the left cylinder bank ... I've never had the need nor time to
> investigate, but I fully expect that one of the ground lugs provides the
> reference for the sensors and the other for the driven components ...
> but through the Kostal connectors multiple signals called "ground" pass
> through different pins.  There may also be splices within the confines
> of the wiring looms ... if you've got a more involved grounding problem
> you're going to have to dig in and understand this sort of thing more
> completely ...
>
> Steve B
> San Jose, CA (USA)

This is something I've wondered about for a while. There are three different 
ground paths shown in the manual. I've been curious about where they get 
their grounds from. I figured in the ECU, but don't know for sure. If they 
are external, what is the harm in finding the solder joints and attaching 
another wire and running it to a good ground?

What leads me to this is I have a permenant Check-Engine light in mine. The 
code pulled is a bad ground for the O2 sensor. As it has a new four wire, 
and I've run an additional ground from the body to the engine, I'm at a 
loss. Oh, it also had the light with the 3-wire original, and with the last 
4-wire replacement. And, I've changed the ECU (different problem). So, does 
anyone have answers? Are those grounds terminating at the back of the 
engine?

Tony Hoffman