Boost Curve for AFB (Troubleshooting)

Hi everyone,

In collaboration with GarfieldMZ, another VAG-COM tuning curve has been created, this time for the AFB (V6-TDI) engine. GarfieldMZ is experiencing some issues with the engine, but he will provide more details himself. For now, I'm posting the diagram I generated from his data, along with two observations:



"Valve" typically refers to the control of the turbocharger boost pressure, expressed in parts per thousand.

First comment:

The tips are quite sharp, IMO, possibly indicating hanging VTG (Vintage).

Second comment:

The regulation seems to work in the opposite way compared to the one used in ASV systems. In ASV, a lower actuation ratio results in a higher maximum charging pressure, while here it appears to be the other way around.

What do you think?

Best regards,

Jan.

Hello Jan,

Interesting curve. I assume this curve was determined under full throttle?

Hi Michael,

yep, klar. Waren die gleichen Messbedingungen wie bei meinen Kurven: 3. Go, full throttle.

More details about it will probably be posted by GarfieldMZ himself, I just created the diagram .

The ASV results look a little different, don't they?

Here's a direct comparison, showing the curve of the ASV:



Best regards,

Jan.

P.S.: Please don't be alarmed if the diagram was unavailable earlier today - one of our core network switches failed.

Hello everyone!

First of all, THANK YOU to Jan for the diagram!

I'm still unable to determine whether this whole situation is actually a problem, or whether it truly aligns with Audi's statement that 'it has to be this way.'

The curve was taken in third gear with full throttle.

As you can clearly see from the curve in the first post, the boost pressure increases steadily with increasing engine speed and has a rather large peak at around 2300 RPM. What is unfortunately not so clearly visible is that at that moment, the thrust suddenly feels noticeably stronger than in the range below 2300 RPM. In the lower gears (1-3), it feels like someone is flipping a switch around 2300 RPM and turning on the 'afterburner' . Some time ago, someone here already noticed a similar effect with the same engine, but no solution or explanation was found in this forum. My inquiry to the Audi technician only resulted in the answer 'that's how it's supposed to be' .
I can actually live with the whole thing, even though it still won't completely let me be , because I had never experienced such a 'switch-like' effect before with any of the three TDi engines in the Golf (90PS, 110PS, and 115PS PD).

Maybe someone actually knows how it happens and whether anything needs to be done or can be done about it!

Jan: perhaps it would be possible or advisable to include a curve representing the target pressure!?

Thank you for your help and ideas!

Regards,

DENNIS

Hi Dennis,

I haven't considered it necessary so far, because the curves follow each other well, but it's actually a good idea - and here it is:



Hmm... it does indeed look interesting - at the beginning, the boost pressure lags behind the target for a while, and I suspect that's due to the turbocharger spooling up, but at the end, it's perfect - so perfect that not only do the lines overlap, but the numbers are even identical.

Also, it's also interesting to compare this to the ASV (Adaptive Speed Valve) system. Here, the target value extends beyond 2000, while the maximum target value for the ASV is 1999. For the AFB (Air Flow Bypass) system in region 2122, this value was the highest, and it's also interesting that the maximum value is only reached significantly *after* 2000 revolutions – perhaps to prevent the overswing from being too steep.

That's all from me... I'm curious to see what the others have to say about the diagram and the problems.

Best regards,

Jan.

Hi everyone.

I also have the AFB in my A4 Avant Quattro, and I experience the same pressure effect at a certain RPM.
I have always attributed this to several factors:

1. In this engine, the maximum torque is reached 'only' at approximately 2100 rpm. However, in the four-cylinder engine, it is reached at 1850 to 1950 rpm.
2. This is an engine with 4 valves per cylinder. Anyone who has driven a four-valve engine as a gasoline engine will confirm that it often feels a bit weak at low RPMs and only develops its power at higher RPMs.
3. The AFB is still a very old component with a wastegate and an 'outdated' distributor injection pump. While impressive in 1997, this technology seems antiquated today, especially considering that 1.9L diesel engines now achieve the same power output with even more torque.

For me, the boost pressure curve looks exactly like how it feels.

Stefan.

Hello Stefan,

I still think that power is being wasted here. The low-pressure phase during boost pressure adjustment seems much too low and long, and I don't think that's normal. However, I don't have any experience with this engine and can't judge whether the boost pressure control system is generally that bad. I would definitely check the boost pressure control system in this case.

Best regards, Rainer.

Stefan: I'm having a hard time believing that about the wastegate?! That thing is a VTG turbocharger! After all, it also has a pressure sensor and an adjustment linkage....

Rainer: I thought so too, that the bottom part is too small. Unfortunately, I lack the comparison curves that could confirm this. Where would YOU start looking? If it's a VTG loader (which I assume it is), would it help to rotate it slightly on the rod?

Regards,
DENNIS

Hi.

Could you please check the following?
- Is it difficult to adjust?
- Is the pressure/vacuum sensor defective? (I don't know your motorcycle model.)

It might help to simply let the engine run with alternating full throttle and no throttle for 3 seconds each time. Then, measure it again immediately afterwards.

Best regards, Rainer.

Hi Dennis,

Just as a side note: Wastegate turbochargers ALSO have a pressure sensor and linkage. So, this is not a definitive indicator of a variable geometry turbocharger.

It might explain the seemingly strange control mechanism, which operates in the opposite way to that of the ASV.

In my opinion, a difference would be that variable geometry turbines (VTGs) are controlled with vacuum pressure, while wastegates are controlled with positive pressure, but that's just my understanding, so don't rely on it – it's better to wait and see if someone with more experience with wastegate turbos has something to say about it.

Best regards,

Jan.

I only have a mechanical LDA.
Here are some data points; perhaps someone can tell me if they are okay. I unfortunately don't have any target values; these were obtained with the engine running at full throttle in 3rd gear. Several measurement series were performed, and the average was calculated.

Engine speed, boost pressure.
1000 1100 mbara
1500 1250 mbara
1600 1375 mbara
1800 1625 mbara
2000 1750 mbara
2200 2000 mbara
2400 2100 mbara
2600 2200 mbara
2800 2250 mbara
2800 2250 mbara

Lowest measured charging pressure: over 2800 1/min, 2200 mbar. Highest measured charging pressure: 2300 mbar.


It seems like the turbocharger is a bit hesitant at the lower RPMs. I don't have anything to compare it to, just this graph.

Best regards, Johannes.

Hello everyone...

I know the article is very old...
I am gradually working my way through the 'catacombs' of the forum...
I would like to know if there's anything new here.
I can observe the same phenomenon on my AFB.
However, this only occurs under partial load and only since it was re-chipped.
Before the chip was installed, the perceived power output ranged from LL (low level) to approximately 3500-4000.
Perceived changes due to the chip:
The pressure builds later, but it's more intense, and the boost lasts until just before the rev limiter kicks in.
P.S. The turbocharger in the V6 TDI is definitely a variable geometry turbocharger (VTG).
I therefore suspect that the phenomenon is related to the motor speed, or rather, the motor's load.
What does this have to do with the guide vanes?

Greetings.
Steve.

So, I've actually observed this kind of irregular behavior in an AFB motor before.
"This is about a car where the mass airflow sensor (LMM) was defective, and I subsequently took it for a test drive (using VAG 5051)."

One might think that the VTG (variable transmission gear) is malfunctioning, but it's not. I've checked it.
He couldn't explain why the car was making that excessive noise. The car hadn't been chipped.

Have you ever tried a new control valve just for fun?

Steve wrote:

Perceived changes due to the chip: The pressure builds later, but it's more intense, and the boost lasts until just before the rev limiter kicks in. P.S. The turbocharger in the V6 TDI is definitely a variable geometry turbocharger (VTG). I therefore suspect that the phenomenon is related to the motor speed, or rather, the motor's load. What does it have to do with the rudder blades?

Hi,

Chip tuning is essentially all-powerful!
Therefore, it is possible that the tuner also made some changes in the area of charger control (which, of course, is controlled by the position of the guide vanes), possibly to suppress excessive overshoots in certain operating conditions.
Perhaps he also lowered the soot limit in the engine's speed range to avoid problems during the emissions test.
-> Just ask him .

Hello Steffarn...

I hadn't given much thought to this behavior until now, because I believed that the chip was the cause.
I only became aware of this phenomenon after reading about it here.
I'm going to try a new valve.

Regards,
Steve.

Hello Ulf...

I hadn't even thought about soot reduction yet...
And I really hope that he didn't change the charging curve.
I assumed he wanted the chip to appear even more 'powerful.'
I hadn't even thought about a technical background.
I will definitely ask questions.
Now I'm curious.

Best, Steve.