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verdiener Guest
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11-03-2004, 14:12 Subject: Chiptuning: ASU & Black Smoke Explained |
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Hello,
I still need to go to the TÜV this month for the main vehicle inspection (HU) and the exhaust emissions test (AU/ASU).
My Audi A4 TDI has been chipped for 50,000 kilometers. That's why it smokes quite a bit when you accelerate.
Is the particulate matter emission measured during the vehicle inspection (ASU)? What are the tolerance limits?
What are the experiences like? Can you pass the emissions test without any problems, even with black smoke due to chip tuning?
Translated on 25-08-2026, 10:43.
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dieselschrauber Administrator


Joined: 04/12/2002 Posts: 18083 Karma: +797 / -0 Location: St.Gallen 2018 Volkswagen T6 
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11-03-2004, 14:24 Subject: Chip Tuning & Black Smoke: Causes and Solutions |
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verdiener wrote: | Hello,
I still need to go to the TÜV this month for the main vehicle inspection (HU) and the exhaust emissions test (AU/ASU).
My Audi A4 TDI has been chipped for 50,000 km. | Therefore, it smokes quite a bit when you accelerate. verdiener wrote: |
Nothing good.
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Is the particulate matter emission measured during the vehicle inspection (ASU)? verdiener wrote: | What are the tolerance limits?
Yes, I don't know the permissible turbidity offhand; it should also depend on the pollutant class. For Euro 2, I believe it's around 2.0/m.
What are the experiences like? Can you pass the emissions test without any problems, even with black smoke due to chip tuning? | }}
Probably not...
Translated on 25-08-2026, 10:45.
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verdiener Guest
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11-03-2004, 17:44 Subject: Chiptuning: ASU & Black Smoke Explained |
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@ Rainer K.
What does 'Nix gut' mean?
'Isn't it normal for TDIs to produce a bit more smoke after being chipped?'
Translated on 25-08-2026, 10:47.
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Rudi Guest
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11-03-2004, 17:52 Subject: Chiptuning: ASU & Black Smoke Explained |
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Actually, not  .
Best regards, Rudi.
Translated on 25-08-2026, 10:47.
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verdiener Guest
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11-03-2004, 18:29 Subject: Chiptuning: ASU & Black Smoke Explained |
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It's not as strong as some people are reporting in this forum.
You can only see it in the rearview mirror at night, reflected in the headlights. During the day, you can only see it if you're driving behind my car.
Translated on 25-08-2026, 10:48.
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palmstrollo Guest
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11-03-2004, 22:26 Subject: Chiptuning: ASU & Black Smoke Explained |
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With proper chip tuning, there should be no increase in smoke compared to the original state.
Before your TÜV appointment, drive a few kilometers with the car and 'blow' it out a bit. This should help to clear out any large amounts of soot particles that may still be in the exhaust system and intake manifold (is the EGR already broken?).
Since the diesel engine is run without load up to its maximum speed during a dynamometer test, the turbocharger pressure is not high, and the soot emissions should be similar to those of an unmodified engine.
My 1Z models have all passed the initial inspection (AU) without any issues so far, even with the chip installed.
Regards,
Hermann.
Translated on 25-08-2026, 10:49.
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Manuel Thomas Guest
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13-03-2004, 22:41 Subject: Chiptuning: ASU & Black Smoke Explained |
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Since the diesel engine is run without a load and up to its maximum speed during the dyno test, the turbocharger pressure is not high, and the soot emissions should be similar to those of an unmodified engine.
Regards,
Hermann.
Objection! Since the examiner is forcing the pedal down onto the floor, and the free acceleration only lasts for 1.2 seconds, the EDC system can hardly compensate!
Mine is producing 1.35 bar of pressure during free acceleration!
Regards,
Manuel.
Translated on 25-08-2026, 10:51.
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wollif Guest
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15-03-2004, 14:13 Subject: Chiptuning: ASU & Black Smoke Explained |
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Hello verdiener,
My experience: Directly from the highway to the inspection station, without an emissions test -> sticker obtained.
Unfortunately, it didn't work out with the use of agricultural roads and without using the highway.
Regards,
I'm sorry, I don't understand the word 'wollif.' Could you please provide more context or clarify your request?
Translated on 25-08-2026, 10:52.
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palmstrollo Guest
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15-03-2004, 14:19 Subject: Chiptuning: ASU & Black Smoke Explained |
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That was also once the advice of my TÜV inspector. Before the emissions test, he suggested giving the car a good run on the highway (of course, he didn't mention anything about the AGR  ).
Regards,
Hermann.
Translated on 25-08-2026, 10:53.
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Uwe Profi-Schrauber

Joined: 04/15/2002 Posts: 1004 Karma: +5 / -0 Location: Westerwald
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15-03-2004, 15:50 Subject: Chiptuning: ASU & Black Smoke Explained |
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I took my car for the emissions test myself on Friday after months of winter inactivity. I don't have a highway nearby, so I just made sure to warm it up properly and gave it some throttle. After that, it passed the test without any problems.
Vehicle: AHF (110 horsepower), 170,000 km mileage, chip installed since 140,000 km.
Best regards,
Uwe Kundenservice bedeutet bei Audi, die Kunden so schnell über den Tisch zu ziehen, daß sie die Reibungswärme als Nestwärme empfinden!
Translated on 25-08-2026, 10:54.
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verdiener Guest
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16-03-2004, 18:40 Subject: Passed AU Exam: Your Success Story! |
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I went to TÜV Nord today and had the vehicle inspected (HU) and emissions test (AU) done.
Passed the exhaust emissions test with excellent results!
The idle speed, the rated speed, the opacity value, and the acceleration time were measured.
Several measurements were taken, and then the average value was calculated for each one.
The opacity value (k-value) of the exhaust emissions was 0.11/m. The legal limit is 2.00/m, and before the chip tuning two years ago, my value was 0.6/m.
By the way, I followed the tips and gave it another run on the highway beforehand.
Besides that, I noticed that the remaining target values on the AU certificate from 2002 differ somewhat from today's values. The tolerances for the speeds were significantly larger. Is there a legal reason for this?
Translated on 25-08-2026, 10:56.
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