Date: Wed, 30 Jul 2014 14:23:29 -0700
Reply-To: Neil N <musomuso@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Neil N <musomuso@GMAIL.COM>
Subject: Re: Another question about O2 sensors..
In-Reply-To: <53D95E85.1040904@cox.net>
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Don. I don't wish to mislead your search for O2 perfection, but Marks
comments reminded me of the O2 connector on my swap engine. (Motronic)
Image of connector: http://tinyurl.com/kdgvmkg Though the wire
colours etc. are different, is this what you see? If so......
I'd asked of this black wire some time ago. Looking online at a more
user friendly Motronic wiring diagram, that black wire leads to the O2
shield which connects to the engine block (ground).
Seeing that black lead led me to believe that it wasn't connected. If
memory serves, in it's OEM form, it was looped "back" and taped"
within the harness. I'd simply uncovered it during wiring harness
work.
Neil.
On 7/30/14, mark drillock <mdrillock@cox.net> wrote:
> Unless you know the exact year and model car that your inline 4 wiring
> harness came from it may be difficult to know exactly how it should be
> connected. Because VW used different variations of that 4 pin O2 sensor
> wiring there is no guarantee that what you had before was right either.
> The old O2 sensor may not have been an exact match to the one that
> harness was fitted with from the factory.
>
> In any case, the shield for the coax should be grounded but only at 1
> end. So it needs a ground at one end and no connection at the other end.
> Never should both ends be connected to ground. From your description my
> guess is you have a harness where the shield is connected only to pin 3
> of the 4 pin. If so that would mean it should have a wire running from
> there to the engine, grounded to bare metal.
>
> But even if that capped wire is supposed to be grounded it is possible
> that you would notice no big difference by doing so. That is because the
> grounding of the shield is only to let the shield absorb stray
> electronic noise that otherwise could be picked up by the inner signal
> wire. Since the normal O2 sensor signal is so small, the circuit is more
> susceptible to interference and that is why the signal wire from the
> sensor to the ECU gets the coax shielding. So grounding one end of the
> shield lets it protect the signal wire from electronic noise but it
> isn't used by the ECU for processing the O2 sensor signal. It is not the
> reference ground, that is elsewhere.
>
--
Neil n
Blog: tubaneil.blogspot.ca
'88 Westy http://tinyurl.com/c8rlw6p
'81 VanaJetta 2.0 "Jaco" http://tubaneil.googlepages.com/
Vanagon VAG *Gas* inline-VR Engine Swap Group:
http://tinyurl.com/d7gd5ej
