Air/Fuel Gauge Install Tip

[Alan Kramer]

Yes, I've done that when troubleshooting CIS...but you still have potential 
for reading a false 0.5V from the computer if it thinks the oxygen  sensor 
reading is whacked.   Here's a good experiment to try:

Disconnect the OXS / ECU plug in the engine compartment.  Connect voltmeter 
to ECU side of plug, the other side to ground.  Start the car.  You'll get 
around 1/2 volt...  this is the false signal from the ECU when it gets a 
whacked reading from the sensor.

Now imagine what happens at WOT with a lean mixture (you can actually do it 
by leaning out the mixture screw and driving but I don't recommend).   The 
oxygen sensor reading drops down to 0V as the car leans out.  After ~ 2 
seconds at 0V, the computer says "Hey, oxygen sensor isn't there, so here's 
a nominal 1/2 volt on that circut"   You might think that the car is now 
running ok, perhaps not as rich as you'd like at WOT, 'cause your guage now 
reads the 1/2 volt...but watch out the oxygen sensor was trying to tell you 
you're in fact dangerously lean and the computer overrode the signal because 
it thought it wasn't true.

But, if your car is in tune at WOT, your voltage should be around 0.6V.  
Even though you're in open loop, the computer sees 0.6V and says "Hey, 
oxygen sensor is still there" and won't mess with the reading.

So, if you trust your state of tune, you can use just the factory oxygen 
sensor and connect as you said.  If you're skeptical, or simply enjoy 
welding like me, put a second one in.

Alan


>From: "Alexander van Gerbig" <Audi_80 at email.msn.com>
>To: "Alan Kramer" <ackramer at hotmail.com>, <rdeis at io.com>
>CC: <quattro at audifans.com>
>Subject: Re: Air/Fuel Gauge Install Tip
>Date: Thu, 17 May 2001 14:42:57 -0400
>
>     OR you can tap into the OXS right at the ECU plug where it splits into
>two non-sheathed cables.  That is what I should have done, but I just 
>didn't
>get it until I had already chomped into the sheathed cable.  I think the
>best way would be to just tie in another wire at the spade for the
>non-sheathed OXS wire in the ECU plug.  I had to route the outer sheathing
>through a bridge wire and then tap into the inner OXS wire.  My gauge
>fluctuates when I am just cruising and idling, then under full acceleration
>it goes rich, under decell it goes full lean because of the cutoff.
>
>Cheers!
>
>Alexander van Gerbig -- '88 80
>
>The Audi  80 Pages-----------------
>http://surf.to/the80pages.com
>
>North Ferrisburg, VT 05473
>
>

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