Oxygen Sensor
Huw Powell
audi at humanspeakers.com
Wed May 27 10:49:15 PDT 2015
The ISV...
First, make sure everything else is working and there are no egregious
intake leaks.
The car should be warm and have a fairly steady idle at 800 (or is it
850?) +/- 50 rpm. I'd accept +/- 150 rpm on a car from the 1980s. If it
does that the ISV is working.
If you then disconnect the idle/WOT switches (effectively turning "off"
the idle switch), the idle will probably go up, and will probably
oscillate a bit over a few second cycle. (You have turned off the ISV,
and now it is at its rest position, letting in a fixed amount of air, so
the idle varies with the mixture changes due to the OXS)
Personally, if one of these things idles under 1000 rpm most of the time
and doesn't stall (ie, is very drivable) I'd be fixing everything else
first.
I put a smoke machine on my '88 90Q after mildly bungling the
installation of a new black rubber fuel dist/TB boot. Apart from the
obvious massive leak under it where a hose wasn't seated properly, smoke
came out "everywhere" - butterfly shaft bearings, places like that.
Those will all be small intake leaks that can contribute to a higher
idle. After the big leak fix, the car is perfectly drivable, though, so
I don't worry about it.
- Huw
On 5/27/2015 1:07 PM, David Vanden wrote:
> Yes, now I feel stupid I was measuring milliohms and not ohms. When I
> measure it in ohms it reads infinity. Another question. How can you
> tell if the Idle stabilization valve is working?
>
> On Wed, May 27, 2015 at 11:19 AM, Huw Powell <audi at humanspeakers.com
> <mailto:audi at humanspeakers.com>> wrote:
>
> Ah, I see, you have an auto-ranging meter, silly me. I still use
> the Micronta I got in the 80s, which I set to 300 ohms when testing
> continuity, so of course it goes off-range when "open".
>
> Yours selects an appropriate range. What you are getting is "close
> enough to infinite" I am sure. You're measuring the resistance of
> the path through any dirt, insulation, and the air and nothing else.
>
> And good catch, you need that idle switch to actuate before
> troubleshooting the idle! Remember I said what a pain it is to
> install correctly "on the car".
>
> You might want to read a lot of this site and digest/bookmark
> whatever seems useful, especially the middle drop-down on the left
> (1980-87 4000, Coupe, UrQ) since there is a lot about your car there:
>
> http://audi.humanspeakers.com/index.html
>
> I hope you also have the Bentley repair manual by now.
>
> - Huw
>
> On 5/26/2015 10:33 PM, David Vanden wrote:
>
> Well apparently the button on the bottom wasn't getting pressed
> because
> the location of the switch must have slipped, so adjusting the
> location
> of the bottom switch tomorrow will be a good place to start.
>
> What was weird was after I pressed the bottom switch manually the
> readings for both sensors began reading infinity when not
> pressed. Just
> before that the top one was reading 20.82 mohms of resistance
> when not
> pressed and the bottom one was reading approx. 3.82 mohms when not
> pressed. I will have to see what they read tomorrow. At least
> I know
> what I have to do with the bottom switch. Thanks all. Good Night.
>
> On Tue, May 26, 2015 at 9:39 PM, Huw Powell
> <audi at humanspeakers.com <mailto:audi at humanspeakers.com>
> <mailto:audi at humanspeakers.com <mailto:audi at humanspeakers.com>>>
> wrote:
>
> What DO they read?
>
> Please give us numbers when you take measurements...
>
> You don't have to buy a smoke machine! EVERY repair shop
> worth its
> salt will have one, and they are simple to set up.
>
> All they do is take very low air pressure from a compressor
> line and
> heat up some special oil to make the smoke, IIRC. Pull a
> vacuum line
> and pump the smoke into it.
>
> On 5/26/2015 9:11 PM, David Vanden wrote:
>
> Well I am pretty sure I got them wired correctly. The only
> problem, as
> I mentioned is that they are not reading infinite when
> open.
>
> There has got to be a way to locate vacume leaks
> that does
> not require
> buying a smoke machine. However, if I did is there a
> model that you
> recommend. They come in all shapes and sizes and
> prices on EBAY.
> Anyway, I will debate it more in the morning.
>
> David
>
> On Tue, May 26, 2015 at 8:17 PM, Huw Powell
> <audi at humanspeakers.com <mailto:audi at humanspeakers.com>
> <mailto:audi at humanspeakers.com <mailto:audi at humanspeakers.com>>
> <mailto:audi at humanspeakers.com
> <mailto:audi at humanspeakers.com> <mailto:audi at humanspeakers.com
> <mailto:audi at humanspeakers.com>>>>
>
> wrote:
>
> Well, they are just switches.
>
> When closed they should read zero or as close as
> possible
> (definitely less than one ohm). When open your meter
> should just
> read off scale/infinite.
>
> They won't "vary" anything, the idle switch tells
> the ECU
> to use the
> ISV to maintain about 800 rpm (and kills fuel if it is
> above ~1400
> rpm). The WOT switch tells the ECU to go into open
> loop with a
> richer mixture for enhanced acceleration.
>
> - Huw
>
> I hope you got them wired correctly.
>
>
> I soldered a set of the throttle body switches
> I got.
> Unfortuneately,
> they read they had some resistance as opposed
> to being
> infinite
> when the
> switches were not activated. I don't know what
> happened to them
> in the
> process of pairing and soldering them.
> However, they
> were both at a
> perfect 0 when activated so I used them. I
> don't think
> they would
> increase the idle?
>
> This is a 1987 Audi 4000 Quattro.
>
>
>
>
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