Boost Pressure Issue, Q7 3.0 TDI (ASB)

Hello everyone,

After several visits to workshops with only partially successful results, a relative contacted me about his Q7 because it has the same engine as my Allroad. Having had a successful experience with my own car, he hoped for the same outcome.

Sure, please provide the text you would like me to translate from German to English.

The car consumes significantly more fuel above 2500 RPM in the partial load range compared to a year ago (30-50%), while the increase is only 10% at higher loads (e.g., accelerating quickly on the highway or towing a boat).

It's a 2007 Q7 with ASB (233 hp) and 270,000 km on the odometer.

"Injectors were replaced at 190,000 km, and they are currently running slightly rich."
2. Have the intake manifold flaps with actuator repaired during the same service.
"3. The DPF (Diesel Particulate Filter) has already been cleaned by a specialist company, and a new differential pressure sensor has been installed. The maximum differential pressure I measured, while driving uphill in 4th gear with full throttle, was 442 mbar. However, instead of the VAG 07Z906051A (with two mounting holes) as listed in my documentation and the AKTE catalog, a Bosch 0281006005 is installed."

Since the troubleshooting process began in the fall, the following has been done by the workshop:

4. New EGR valve and pressure transducer.
"Initially, the suspected cause was a loss of boost pressure, with a deviation of 10-15% observed. The intercooler system was pressure tested and found to be leak-free. A visual inspection identified a turbocharger with a leak on the compressor side, which was then repaired. Since then, the boost pressure has been at 100% as expected. However, this did not result in an improvement in fuel consumption."
6. New coolant temperature sensor.
7. The mass airflow sensor was also recently replaced (with a Denso unit, not a Bosch one), but it didn't improve the situation either.

Okay, now let's talk about the phenomenon I observed. Up to 2500 RPM, all the values are actually green.

Bei 4000 U/min im 3.Gang (also wenig Last) habe ich stationär eine soll/ist Abweichung bei der Luftmasse von über -30%. Bei 4000 U/min im 6.Gang (fast Vollgas) nur noch -5%. Ladedruck soll/ist passt 100%. [EDIT] Ach ja, bei wenig Last geht trotz der sehr hohen Drehzahl die Ansteuerung des AGR-Ventils auf 80%. Ist es möglich, dass das MSG bei so hoher Drehzahl noch AGR machen möchte? Ich dachte immer da sei bei 2500 oder 3000 U/min Schluss! [/EDIT]

I measured everything I could think of... everything looked healthy and reasonable (unfortunately, the records were deleted). What else should I be paying attention to? What am I not seeing? The car is in Switzerland, and I'll be going back there in about 3 weeks.

Two specific questions:
A: Can anyone confirm that the Denso DMA-0210 mass airflow sensor has the same characteristic curve as the original when viewed from the top?
B: Can anyone confirm that the Bosch differential pressure sensor 0 281 006 005 has the correct specifications? It's listed in the Bosch catalog as the only option for that vehicle, but AKTE doesn't recognize it for that car!

Thank you and best regards.

Okay, please provide the German text you would like me to translate.

The forum is changing "E-T-K-A" to "AKTE" and I can't correct it. What am I doing wrong?

Ste.Bo wrote:

... What am I doing wrong?

Nothing...

Ste.Bo wrote:

Hello everyone, Two specific questions: A: Can anyone confirm that the Denso DMA-0210 mass airflow sensor has the same characteristic curve as the original when viewed from the top? B: Can anyone confirm that the Bosch differential pressure sensor 0 281 006 005 has the correct specifications? It's listed in the Bosch catalog as the only option for that vehicle, but AKTE doesn't recognize it as being compatible with the car! Thank you and best regards. Bo

.

Hello.

Regarding A:
According to statements from others who have already installed it, it is supposedly not "perfect" .
Original: 059 906 461 K ist er von Hitachi für Audi hergestellt worden. HitachiNR. AFH 70-46

If you buy an original Hella mass airflow sensor (part number 8ET 009 142-791).
Can you obtain an original Audi/Hitachi part (with the Audi part number removed)?
The Hitachi part number 70-46, as indicated on the original, is present, and it has a Hella color stamp on it. The current price is around €110 from various suppliers; you can easily find it by searching online.
I installed it myself in my ASB, and I can only recommend it. It's a great way to get an original part for only 30% of the cost.

"Regarding part B: I find the sensor to be a standard one with the part number 07Z906051A, and it can be replaced with a Bosch 0281002710, which replaces the previous part number 0281002558. It costs €35 at Bosch."

Regards, Mpire.

Hello Mpire,

Thank you for the input. I was almost certain it was an LLM.

I'm not sure if I understood you correctly regarding the DDS.

Mpire wrote:

"Regarding part B: I find the sensor to be a standard one with the part number 07Z906051A, and it can be replaced with a Bosch 0281002710, which replaces the previous part number 0281002558. It costs €35 at Bosch." Greetings Mpire

.

When I decode the Vehicle Identification Number (VIN) on the Bosch website, I get a different Bosch part number (see image) than the one I find when searching for comparable part numbers for 07Z906051A in AKTE or on the Bosch website.

My assumption is therefore that all four contain the same thing.

Hello everyone,

After a long time, I finally got to drive a Q7 again.
In the meantime, an original mass airflow sensor (MAF) and a digital dashboard display (DDS) with the original part number (which is also listed in the AKTE parts catalog) were installed.
The AGR valve has been reassembled and tested.
When the engine was cold, the EGR bypass valve and EGR cooler were inspected, and a slight leak was detected at the valve shaft.
The intercooler piping is still completely airtight!

Nothing has changed.

I'm at the end of my rope with my understanding of this system. How can I have full boost pressure while simultaneously having a 10-20% air mass deficit?

"We tried it with a new air filter and even without one. It made no difference. Furthermore, the lower the load and the lower the target boost pressure at high RPMs, the greater the percentage of air-fuel mixture deficit."

Do you have any ideas? What else could I log to figure out what's going on?

Regards,

Okay, please provide the German text you would like me to translate.

Hi,

What is the mileage? Also, is the DPF possibly clogged with ash?
Have you ever looked at the differential pressure? There's a topic here with comparison values.

Ah, I just saw that you're setting the target value for the missing air mass. You can ignore it; based on my assessment, the actual air mass seems to be okay given the boost pressure.

The air mass is only regulated in the partial load range; when you're at full throttle, you can ignore the target value.

Best regards, Rainer.

dieselschrauber wrote:

Ah, I just saw that you seem to be fixing the missing air mass to the target value. You can ignore it; from what I can see, the actual air mass looks okay for the current boost pressure.

Ah, okay. What else should I base it on? Just boost pressure? Then I would need a data sheet for the turbo or as much experience with these "small engines" as you .

dieselschrauber wrote:

The air mass is only regulated in the partial load range; when you're at full throttle, you can ignore the target value.

My current problem is with the regulation in the partial load range. Full load usually works fine (with rare minor deviations).

The car now has 275,000 km on the odometer. The DPF (Diesel Particulate Filter) has been cleaned and now has very good regeneration values.

I just drove it again. What's concerning me is that at 3200 RPM in 5th gear and 4100 RPM in 4th gear, while maintaining a constant speed of 140 km/h on the highway (i.e., under partial load and steady state conditions), I'm seeing deviations of 20-30% between the target and actual air mass, and the EGR valve is open (see pictures). I always thought that the EGR system wouldn't be active at those high RPMs!

Just had another thought. Could it be that carbon buildup on the piston rings causes so much blow-by that the amount of fresh air entering through the EGR valve is significantly reduced? This would explain why the problem gets worse with increasing engine speed.

Well... I'll gather more ideas until my next visit.

Regards,

Okay, please provide the German text you would like me to translate.

Hello Bo,

In your logs from the previous post, you're showing very low boost pressure. Without doing any calculations, the actual air mass values look okay. Also, the duty cycle seems to be correct for the target value.
I would say that the regulation simply sets an unrealistic target that cannot be achieved.

The regulation is definitely active in idle and low-load conditions; just check if the target value is being reached.

Best regards, Rainer.

Okay.

Everything adjusts and works perfectly in the lower section.

According to the Lambda readings, there seems to be more than enough fuel for combustion. What confused me was the difference between the target and actual values.

Thank you. I won't bother you with this anymore.


Regards,

Okay, please provide the German text you would like me to translate.

You're not annoying. X