Got sooty exhaust tips? MAF is the primary suspect, but got some new O2 sensors in too (long).
06-16-2005, 09:07 PM
#1
AudiWorld Super User
Thread Starter
Got sooty exhaust tips? MAF is the primary suspect, but got some new O2 sensors in too (long).
Got an O2 socket too, but have not installed it. Actually don't know that I need to now. My concern started with the fact that my exhaust tips are ALWAYS sooty. I mean after running 1/4 tank of gas, my tips would get REALLY sooty. This has happened since I got the car over two years ago, and before I did ANY mods to the car. For comparison, MarTT can go several tanks of gas and have less soot than me after 1/4 tank. We have all the same engine mods now, except he is APR vs. my Revo.
So, we finally got around to VAG-COMing my car. I suspected all along that the calibration of the O2 sensor MUST be off, and the car must have been upping the fuel ratio incorrectly. However, the VAG-COM showed (via block 003) that the flow through the MAF was low (peaking at ~130 g/s at full throttle, where it should be ~180 - this is with a new V2 **** on a 225). So, we put in a new rebuilt Audi MAF that MarTT had on hand. Values went up a little, to ~140-150, but that was still not where they should be (20% low). After a couple days of head scratching we put in a third MAF, this one a new VW unit. Values for g/s shot up to 180! WooHoo!
Well, on reflection, another thing of interest in the VAG-COM readings is that with the old MAF, the Part Throttle (multiplicative adaptation) readings for block 32 were around +11.5%. This indicates a LEAN condition - we noted that right away as not making any sense. I mean, I started looking in to this in the first place because of SOOT on the pipes, which is a RICH condition by definition (for information, the idle values were near 0, which is where they should be, it was only under load that the readings were high/lean)....
Now it all makes sense, though. Since the MAF was faulty, especially under load, and reading low, there was actually MORE air entering the combustion chamber than was registered by the MAF. This is a lean condition that the O2 sensor was able to sniff out, and it would adjust the car to dump more fuel to compensate. Well, in lower RPMs, where the MAF is likely reading correctly, that extra fuel is still dumping, but it is not needed - so the mix is rich... With errant readings with the MAF the air/fuel mix must have been bumping all over the place depending on how much load was placed on the car, and if the airflow range on the MAF was correct in that region.
Now 2 days into the VW MAF, the readings for Part. Throttle are all that way down to -5.5%. This indicates a RICH condition, and that the fuel injectors are being cut back. This is exactly what SHOULD be happening (I am running a 4 bar FPR with the ****, so it should be rich, but not OVERLY rich like it has been)! We will see over the next few days/tanks if the sooting symptoms subside, but I am encouraged that they will.
So, this post started about O2 sensors...
Here is what I got:
<img src="http://images10.fotki.com/v193/photos/4/435091/2318084/04Cleanbody-vi.jpg">
It is VW PN 06A 906 262 Q and was $24 at www.worldimpex.com .
I also got this guy at Pep Boys:
<img src="http://images10.fotki.com/v191/photos/4/435091/2318084/01HelpfulTool-vi.jpg">
If/when I do get around to changing the sensor, the socket should make the job pretty easy...<ul><li><a href="http://public.fotki.com/mcphill/audi_stuff/o2_sensor_replacement/">O2 Sensor Fotki</a></li></ul>
So, we finally got around to VAG-COMing my car. I suspected all along that the calibration of the O2 sensor MUST be off, and the car must have been upping the fuel ratio incorrectly. However, the VAG-COM showed (via block 003) that the flow through the MAF was low (peaking at ~130 g/s at full throttle, where it should be ~180 - this is with a new V2 **** on a 225). So, we put in a new rebuilt Audi MAF that MarTT had on hand. Values went up a little, to ~140-150, but that was still not where they should be (20% low). After a couple days of head scratching we put in a third MAF, this one a new VW unit. Values for g/s shot up to 180! WooHoo!
Well, on reflection, another thing of interest in the VAG-COM readings is that with the old MAF, the Part Throttle (multiplicative adaptation) readings for block 32 were around +11.5%. This indicates a LEAN condition - we noted that right away as not making any sense. I mean, I started looking in to this in the first place because of SOOT on the pipes, which is a RICH condition by definition (for information, the idle values were near 0, which is where they should be, it was only under load that the readings were high/lean)....
Now it all makes sense, though. Since the MAF was faulty, especially under load, and reading low, there was actually MORE air entering the combustion chamber than was registered by the MAF. This is a lean condition that the O2 sensor was able to sniff out, and it would adjust the car to dump more fuel to compensate. Well, in lower RPMs, where the MAF is likely reading correctly, that extra fuel is still dumping, but it is not needed - so the mix is rich... With errant readings with the MAF the air/fuel mix must have been bumping all over the place depending on how much load was placed on the car, and if the airflow range on the MAF was correct in that region.
Now 2 days into the VW MAF, the readings for Part. Throttle are all that way down to -5.5%. This indicates a RICH condition, and that the fuel injectors are being cut back. This is exactly what SHOULD be happening (I am running a 4 bar FPR with the ****, so it should be rich, but not OVERLY rich like it has been)! We will see over the next few days/tanks if the sooting symptoms subside, but I am encouraged that they will.
So, this post started about O2 sensors...
Here is what I got:
<img src="http://images10.fotki.com/v193/photos/4/435091/2318084/04Cleanbody-vi.jpg">
It is VW PN 06A 906 262 Q and was $24 at www.worldimpex.com .
I also got this guy at Pep Boys:
<img src="http://images10.fotki.com/v191/photos/4/435091/2318084/01HelpfulTool-vi.jpg">
If/when I do get around to changing the sensor, the socket should make the job pretty easy...<ul><li><a href="http://public.fotki.com/mcphill/audi_stuff/o2_sensor_replacement/">O2 Sensor Fotki</a></li></ul>
06-17-2005, 04:02 AM
#5
AudiWorld Super User
Thread Starter
Thats the O2 sensor nut size, remember, not the male hex that drives the socket. As MarTT says, ..
though, the O2 sensor itself is 22 mm. You could not use a SP socket, though, because the wire is in the way.
06-17-2005, 04:39 AM
#6
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Same thing here
I noticed more soot than usual and my g/s was down to ~145 and Part Throttle was +13. Replaced the MAF with rebuilt Audi part and it went back up to 191 but my PT was still high at +11.7. I guess the car hadn't readapted yet. I cleared the codes again to reset the fuel maps and did a throttle body to see if my PT would go back down from +11.7. Haven't checked yet to see if it worked.
What if that number is too high still, what else could cause it? Front O2 sensor?
What if that number is too high still, what else could cause it? Front O2 sensor?
