A6 2.5 TDI: Lack of Power/Top Speed?

Okay, let me briefly tell you about my troubles:

I drive an Audi Avant, model year 1999, with a 2.5 TDI engine and 150 horsepower. Recently, I've noticed a gradual loss of power in my car. I took it to an Audi dealer, and after diagnosis, they replaced the mass airflow sensor and the turbocharger. Now, the car pulls well from a standstill up to about 140-160 km/h. However, above 160 km/h, it takes a very long time to accelerate. The top speed is now only just under 200 km/h, compared to the registered 217 km/h.

'Many people say it's because of the tires. I have 235/18 tires on. But I can't imagine that it's *that* drastic because of the wide tires. Today, I drove with my family (4 adults and 1 dog) on the highway. There was an old Mercedes E200 (136 hp) in front of me, and it was alone in the car. I wanted to overtake it, but then it accelerated, and I didn't gain a single inch on it. That shouldn't be possible, right?'

Does anyone have any suggestions as to what could be causing my poor performance and lack of torque at higher RPMs? Has anyone else experienced a similar issue?

Desperately.

Chris.

What do you mean by "from the bottom"? Do you mean starting from the highest gear of 1200 RPM and going up, or when you fully utilize the lower gears?

In the lower speed range...

On the highway, it accelerates nicely to 180 km/h in 5th gear, but then it becomes extremely sluggish to reach 200 km/h, and at 200 km/h, it's... (the sentence is incomplete).

Best regards,

Christian.

That still doesn't make things any clearer for me.

'I meant that the entire speed range up to 180 km/h is reasonably okay. But above 180 km/h, it's extremely sluggish... It takes almost a minute to go from 180 to 200 km/h, and then it's done...'

Best regards,
Christian.

Are there any error codes stored?
We were just dealing with that... a new mass airflow sensor (MAF) was installed, but 500km later, the performance was low again. We measured it again, and it was still off, so we got a new one under warranty, and it's been running great for almost 5,000km. It's really super... and we can reach 220 km/h again .

The diagnostic trouble codes only showed a sporadically high intake manifold pressure sensor reading. They suspected it was caused by a jammed variable turbo geometry (VTG) linkage.

It's difficult to explain to the Audi workshop that they should install another new mass airflow sensor.

The VTG rod should be fine now, thanks to the new turbo.
Have you ever compared the rolling circumference of your tires with the original tire size, or determined the speedometer deviation?

So, regarding the tires, everything fits. According to the climate control system, the speedometer reading is even accurate to almost exactly kilometers per hour.

HELP

It's obvious that the climate control and speedometer display the same information because they are both powered by the same speed sensor. This would also be true even if the tire circumferences were completely different.

As long as the tires are approved for your car according to the wheel specifications, you shouldn't have any problems. However, it might be helpful to post the full tire dimensions (including the sidewall height!) of both your current tires and the original tires for verification.

Alternatively, one could perform their own assessment of the ease of use of the VTG (Variable Turbine Geometry) system, or conduct a systematic troubleshooting process using a diagnostic tool (e.g., VAG-COM).

In addition, detailed answers and reading the articles (/index.php?c= in this forum are always appreciated .

Okay, then.

Original tire size:

205/55 R16

Current tire setup WITH TÜV (German technical inspection authority) approval and release for my vehicle:

235/40 ZR18

I think the VTG (variable turbine geometry) should be working now, since a new turbocharger was installed. Also, the MAF (mass airflow) sensor is new. However, many people in another forum would still stubbornly insist that the NEW MAF sensor is also defective.

Best regards and thank you for your responses.

Chris.

PS:
I've already read the tips and tricks, but unfortunately, the articles didn't provide the help I need. It would be great if someone else has encountered a similar problem and could help me.

The tire choice accounts for 2% of the performance, not taking into account the different camber settings.
That leaves us with:
- Have the valve timing/injection timing checked.
-Performance test stand, so that you have something to refer to when making a complaint.
- Log and post measurement data using the VAG-COM protocol.
-Alternatively, use conventional measurement techniques, such as manometers and multimeters, to measure anything that can be physically measured.

So, I recently took my car to the ADAC for a performance test.

You can find the results in my attachment. The following can be observed:

1. The vehicle has the intended power output, which is 150 horsepower.
2. The vehicle does NOT have the correct torque, which should be 310 Nm.

'Does anyone have experience with performance diagrams and could tell me what might be causing a 20 Nm power loss? The ADAC inspector said the mass airflow sensor (MAF) is likely fine because a) it's new, and b) if it were faulty, you would see a very noticeable irregularity in the power curve.'

Okay, I'm all out of ideas now. What about you?

Best regards,
Chris.

You can find the performance chart at:

http://www.clan00.de/phpBB/viewtopic.php?p=34124#34124

Please translate the following text from German to English. Provide ONLY the translation, no explanations.

Hello,

The fact that the turbo is new doesn't really say much about whether the boost pressure is correct.

A diagnostic run using VAG Com or a boost pressure gauge will indicate whether the VTG (Variable Turbine Geometry) system is functioning correctly. The EPW (Exhaust Pressure Wastegate) valve seems to be a common source of problems. The message regarding the intake manifold pressure is particularly suspicious.



Good luck, Rainer.

Hi,

Can you explain the spike in the graph at 100 km/h? Otherwise, I would say something is wrong.
You can find a comparison chart at:
http://www.tuneline.at/produkte/diagramm/akn_193.gif


You can see that the torque remains relatively constant from around 2000 RPM, whereas in your case, it's still building up.

The workshop couldn't figure it out either. Apparently, all the data that can be read out with VAG COM seems to be correct. Now they've sent the whole mess to Audi AG, because they're also at a loss.

Okay, I'm going on vacation now. If you want, I can write to you later and tell you how the drama unfolded.

Thank you for your help until then, and see you soon.

Chris.