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Old 09-01-2003, 08:46 AM   #1
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Default Could a faulty O2 sensor cause the car to run poorly and hesistate

a lot?? I've done a few of the bigger mods now and she still doesn't feel like it should. I think I have a bad o2 sensor and am wondering how much of the hesitation could be coming from that. From the VAG it's on of the pre-cat sensors, for what it's worth.
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Old 09-01-2003, 09:02 AM   #2
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Default in three words: Bet yer ***! And if they're both original you'd likely...

be better off adding two instead of the dying one as you can bet the other one won't be far behind. Besides, they both report to the ECU and it would rather receive similar/identical signals than different ones. And while I don't use generics for these I'd rather have 2 generic new ones than one suspicious one. And two generics only costs a little over half of one OEM one. Generics have fine signal ouputs but their heated elements are a lot slower to respond on cold start-up which is easily confirmed with an A/F monitor.

And of course there's no guarantees that this is at the root of your problem. But its a high percentage cause and great place to start. Most any car with 60k+ miles would benefit from new sensors.
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Old 09-01-2003, 09:33 AM   #3
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Default I bet I should have paid better attention...

What are our options for replacing O2 sensors?

There was something about 3-wire vs 4-wire sensors?

And what exactly is the problem with the generic O2 sensor?
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Old 09-01-2003, 09:41 AM   #4
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Default 3-wire up front, 4-wire aft of cats... how hard is it to replace them??

I'm not sure how to tell generic from OEM, but from what I've heard OEM are connectorized and plug right into the sockets.
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1995 S6 Avant Emerald/Ecru - Almost here, not much longer
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Old 09-01-2003, 09:51 AM   #5
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Default The rear ones look like they are hard to remove

It looks like a tight sport, and you have to route the wires somehow...

The pre-cat ones seem to be relatively conveniently located. A crow's foot should do, I guess? Unless the sensors are really stuck (likely?).

So, I could use generic O2 sensors, but I'd have to solder the connectors of the OEM sensors to them? That would be no problem.

Do you happen to have a part number for the generic Bosch O2 sensors that will fit our cars?
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Old 09-01-2003, 10:06 AM   #6
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Default On our cars 3 wire is pre-cat and 4 wire is post cat...

and there's two of each used.

The problem with the spliced in is it take MUCH longer to warm up to it's operating temp than the stock sensor. Likely due in part to the butt splice connectors used tho years ago I tried soldering them VERY lightly and got the same result. There also "may" be some difference in the watt rating in the different O2 sensors heat elements or the Audi output that causes/aggrivates it as well. With a stock sensor my AF gauge will start to go closed loop and dither (swing back & forth from lean to rich) within 60 seconds even at 15* F. The generic ones won't dither until 5 or 6 minutes after starting the car and driving away on a summer day. Doesnt hurt anything as there's still the temp sensor for the ECU to rely on as far as mixtures go but it will stay richer MUCH longer with the generic plug after the OEM plug has settled into closed loop and starts relying on ECU F/A adjustment. The generic plug during this time will just leave one light on usually in the leaner "stoich" range. Meaning the sensor hasn't reached a hot enough temperature to start generating/sending a signal to the ECU. The OEM sensor gets hot enough to "fire" (send an output signal) very quickly in terms of comparison.

As far as the signal itself once both are up to operating temps it doesn't seem to be a problem. But I always hated driving around with the "choke" on for 5 or so minutes as the car has a tendency to shudder/shake a bit as if it were getting too much fuel... which it is. And it happens every time you turn the car off and re-start it even once warmed as the sensors cool down so fast. Tho an OEM sensor'd car is immediately back up to temp the generic one wants to take longer again tho maybe only half as long as a cold start-up, still 8-10 times longer than the OEM sensor'd car.

I just do sensors prophylactically at 50k miles on my turbo cars and 60k miles on my NA one. Tho I just did all 4 new OEM ones on my 12V at 100k miles when I did the exhaust. Actually I did the two front at 98,988 miles when I did the ARC2, F/A monitor and injectors and the rear ones with exhaust at 100,200 miles. Actually I think the rear ones could be stretched out to 100k intervals unless one starts throwing codes as it's a far less harsh environment back there than the front ones. And I believe the rears are only there for a "differential" reading and no info is used by the ECU to make fuel adjustments based on rear sensor output. The reason I think this is because as long as the sensor is good it works fine with no codes even if zip tied up and out of the exhaust system altogether as I confirmed when I did my exhaust. Problem is I don't know how long it will live outside the exhaust, exposed to the elements. And due to the heat they generate on their own ya can't just wrap them in a baggie as they'll melt any plastic they come into contact with pronto. And silicone's out as that is fatal to an O2 sensor just like a MAF sensor. So for lack of finding a suitable solution I screwed them back into the exhaust and figure I have 100k miles to find a way to remove them and get em in some kind of small sealed container... "small" being the key word here otherwise a Thermos would work ;-)
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Old 09-01-2003, 11:00 AM   #7
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Default I've had only one of them replaced

I'm not sure which one it was, but I had it done at about 60k miles. That means, three O2 sensors are over 126k miles old. I guess, I'll soon replace the two pre-cat sensors with OEM ones. I don't want the car to run rich for 6 minutes after a cold start.
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Old 09-01-2003, 11:10 AM   #8
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Default So the OEM ones are simply plug and play??? no splicing?

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Old 09-01-2003, 01:23 PM   #9
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Default That would explain their price...

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Old 09-01-2003, 01:23 PM
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