'86 CGT oxy sensor

[Alan Kramer]

In my experience working on 1983, 1985, 1986 and 1987.5 CGT's, all except 
the 1987.5's have the oxygen sensor mounted in the exhaust manifold just 
after the #5 cylinder by the battery tray.  This is plenty hot for a 
single-wire oxygen sensor.

In 1987.5 the 5-2-1 exhaust manifold was used on the NG motor; the oxygen 
sensor moved down into the downpipe just after all 5 cylinder's exhaust 
gasses combined.  A 3 wire sensor was used from the factory here, because it 
is so far away from the head.

I have never seen an oxygen sensor mounted in the cat on a CGT.  I believe 
this is a 4kq phenomenon only.

Interestingly, the 4kq's 5-3-1 exhaust manifold could have been cast with a 
hole for an oxygen sensor.  There is a flat spot the diameter of an O2 
sensor bung just before the flange to the downpipe.  If a hole were there, 
it would only have measured the O2 for 4 of the cylinders (it would have 
split the wall between the two larger pipes).  For that reason I believe the 
sensor was relocated to the cat, which on the 4kq is the first place where 
all cylinder's exhaust gasses pass together.

My feeling is that if you have the oxygen sensor in the e-m, use a 1 wire.  
If it's in the downpipe or cat, use the 3 wire.

HTH,
Alan

'83 CGT
'86 CGT
'86 4kcsq


>From: Gary Erickson <erickson at teleport.com>
>To: quattro at audifans.com
>Subject: [Fwd: Re: '86 CGT oxy sensor]
>Date: Tue, 03 Oct 2000 09:20:33 -0700
>
>I had originally sent this directly to Craig, but it looks like I should
>have replied to "all."  ;-)
>
>-Gary
>
>-------- Original Message --------
>Subject: Re: '86 CGT oxy sensor
>Date: Tue, 03 Oct 2000 08:56:37 -0700
>From: Gary Erickson <erickson at teleport.com>
>To: "Craig D. Niederst" <niederst at telerama.com>
>
>"Craig D. Niederst" wrote:
>
> > With all this oxy sensor talk, I know my '86 CGT is in need of a new 
>one. It
> > currently has a one wire sensor in it now. I noticed that while this 1 
>wire
> > sensor plugs directly into a single socket plug on the factory harness,
> > there is a 2 wire socket on the same harness that is unused. Does the 
>'86
> > CGT take a 3 wire heated sensor, or is the 1 wire one correct? I've 
>looked
> > in the family album, and its inconclusive. I am hoping replacing this 
>sensor
> > will correct the horrible idle problems and the poor gas mileage (~12 
>mpg
> > according to the trip computer). TIA.
>
>Craig,
>
>The Coupe GT's still had the oxygen sensor mounted in the downpipe from
>the manifold (rather than in the neck of the catalytic converter like
>the 4kq's).
>
>That location is warm enough that Audi continued to use the single-wire
>sensor in the GT's through the end of their life.  (The mythical
>high-compression 2.3l special edition GT's sold as '87.5 models may be a
>different story)
>
>The 2-wire socket that you are referring to is a test point for the CIS
>system to plug in one of the diagnostic tools.  Even if you do find 12V
>there, I wouldn't recommend trying to use it as a power source!  ;-)
>
>The single wire OXS is the correct replacement, if you were willing to
>wire up a power source that was switched with the ignition, you could
>easily install a three wire OXS, but I'm betting any gains would be
>minimal.
>
>HTH!
>
>-Gary
>
>'85 turbo GT coupe
>'89 80q
>'89 200q

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