Bi-Turbo control. Setpoint + Troubleshooting

Hi,

I have a problem with the 3.3L AKF (Common Rail) in the A8 (year 2000).

Symptoms:
The vehicle has wavy acceleration or gentle jerking in the 2,000 RPM range under heavy load (e.g., prolonged towing uphill). Difficult to reproduce in the flat Schleswig Holstein area, so I have to rely on the driver's (my dad's) description of the problem.

Suspect:
Variations in the boost pressure (possibly due to an aging MAF sensor, see below)

Note:
The vehicle has a Bi-Turbo system with 2 MAF sensors (relatively new for me). Both turbos feed into a common (air/water) intercooler. Therefore, they only produce a single boost pressure (I initially thought it had two four-cylinder engines with separate intake systems).

Diagnostic log:
Shows boost pressure mismatch (MWB 21.2) values during the test between -5% and -10% (depending on load and speed). This means it's likely at its limit (according to the label file, it should actually be at +-5%).

Default setting
Field 33 shows 1450 rpm
LMM1 between 120 - 560mg/H
LMM2 between 180 - 700mg/H
Always working in alternation.

My conclusion is that one LMM is measuring significantly less than the other, and therefore needs to be replaced. Unfortunately, I don't know if the LMM2, which measures more, is actually sufficient, or if it should also be replaced.

Whoever has replaced an LMM before, probably replaces both (sitting above the gearbox). "Amateur drivers replaced a faulty part about a year ago, as it was Sunday, and the car needed to be driven on Monday (we only ordered one because we hadn't considered whether it was better or worse to buy a new one (4 cylinders damaged)).

If anyone is interested, I can gladly upload a log with data from 1200-4000 RPM with MWB 21 and 25 (TVs and LMMs). I can also create more if needed.

I would also appreciate any tips on smooth vibrations or wave-like acceleration in the 3.3L common rail engine. Even if someone thinks it's more likely due to the turbos or their surroundings than the LMMs, I would be grateful for any advice. The box... Unfortunately, the setup with two LMMs (left and right manifold), two turbos, but a shared boost pressure, is a bit unsettling for me.

Thank you for the tips.
Best regards,
Guste

P.S.: What surprised me negatively about the design is the possibility that an aging intake manifold permanently directs more pressure to one turbocharger than the other. Why not simply use two four-cylinder engines instead, so that the intake side of the manifold is connected to each turbocharger separately?

If anyone is interested, I can gladly upload a log with data from MWB 21 and 25 (TVs and LMMs), ranging from 1200 to 4000. I can also create more if needed.


Hello Guste,

yes, please upload the logs.
I can't really figure out the cause of the error, but I would first try to investigate the behavior of the two turbos. (as you are already doing) )
Therefore, TV from Turbo (are these VTGs?) would initially be helpful.
Perhaps the software already provides information about the blower behavior.
If only one LD sensor is used for control, it is unlikely that the turbos are controlled differently, at least I don't currently know where the actual values for the different control settings should come from.
Are the KF (control units) for the turbos duplicated?

Please post the STG version, I'll check if I can find an original one..

Unfortunately, the setup is quite complicated, with 2 LMMs (mass airflow sensors), 2 turbos, but a shared intake pressure, which makes me a bit uneasy.
Regards, Jochen

Was was the LMM original?

Hi Guste,

"Approximately 80% of the error is due to uneven LMMs or a one-sided clamping of the VTG mimic, which is typical."

Okay, I'll plan a LOG trip and input the data. Then I'll review the data. I can't give you a precise answer yet, I need to check all the documents in the office.
The Biturbo control is essential for this concept, as different flow differentials would otherwise significantly affect the AGR rates, or different turbine efficiencies would otherwise lead to overspeeding of a turbine.

...and regarding LMM replacement: Replacing only one is illegal - just like the situation with the D2. There were even considerations during development to incorporate maintenance flaps into the floor to enable the HFM replacement from the inside. That pretty much says it all!

Also, schau auch mal die Raildruckregelung an, die CP1 Pumpe war auch ziemlich anfällig. Typical are also injectors that fail sporadically, with the coils having a way to access them - LRR and fault memory with environmental conditions check.

Yes, you can briefly apply the brakes at around 2000 RPM and high load (where the problem occurs) to maintain a constant speed, especially when the SG goes into emergency mode while the brake and accelerator are simultaneously activated – simply press the accelerator twice while braking and then release it again – this will restore the power and allow you to bring the engine speed back to the desired level. This allows the brake to remain free for up to 30 minutes - which is useful if you don't have a test bench handy.
For diagnostic purposes, 60 seconds are more than sufficient - and it's also a good idea to make a LOG during that time.


Greetings

Hello,

Thank you for your suggestions!

Yesterday afternoon, both of us replaced the LMMs (not in the mood to do it again). Unfortunately, during assembly, a plastic part of the diesel line broke, so the final test will have to wait.

I have now graphically improved the log, and I was finally able to clearly identify the oscillating LD. It was barely perceptible during the test drive (without the caravan+hill). Acceleration ranges from 1300 to approximately 3500 (on the highway, highest gear).

The boost pressure takes a long time to stabilize. It also seems to be behaving like a hakelder VTG, in addition to the LMM. I just don't know how to diagnose which of the two chargers is causing the problem, but I'm going to try going through the basic settings to see if there's a suitable block for that.

@Jochen:
Logs anbei.
The overall load pressure is controlled via the load pressure sensor. The load balancing is performed via separate LMMs!

@christians:
LMM was original.

@bafische:
I can only watch the rail pressure control again when it's running.

I have already looked into the LL-smoothing setting: it was relatively unremarkable, with the largest outlier being around 1.15, and all others within +/-1.

Regarding "brake" and "gas", I suspect you mean 30 seconds, not 30 minutes, right? However, this is a good indication, although I think that VTG has already localized the issue as an additional cause.

Were the VTGs you had repairable, or did the turbo need to be replaced? The car is actually not being overly careful (motorways in Schleswig-Holstein are often free), so I doubt that the typical soot-causing emissions are due to constant creeping and the lack of full-power gas engines.

Logs are located at: /viewtopic.php?p=129020

Greetings
Guste

accounts for 80% of the error, which is typically caused by uneven LMMs or a one-sided clamping of the VTG mimic.

Hello Guste,

I would initially agree with that, after reviewing your log file.
The boost pressure varies in the same proportion as the air mass. The VTG control attempts to maintain a constant LD level by making large adjustments to the control signals, but this is not very successful.

The LMM exhibit different torque characteristics at lower engine speeds. IMA can only be caused by the different implementation of the control commands for the turbochargers.
A closed LMM shows low values at high LM. At high speeds, the measurements from both O2 sensors are quite consistent with each other, although the 1 turbo needs to be adjusted more noticeably for this.

I would now be more inclined to look for VTG units with a more 'clamping' characteristic, as I find the LM units to be too constant at high speeds.

Can you tell me something about the fuel injection amounts?
Do you, due to the potential Klemmente VTG, briefly enter the smoke limit, which further intensifies the wavy LD and causes the system to oscillate?

Or, the rail pressure may not be optimal on the bank, which leads to the different performance of the turbos?

Best regards,
Jochen

I believe I am still in debt with a response, even though it has been two years:
We replaced both the LMM and later both the LD-valves, and we made the turbos as functional as possible using "turn signal control". A VTG (Variable Turbine Geometry) remains slightly more difficult to operate with manual overpressure when both turbines are controlled synchronously, but we have not made any further adjustments.

Occasionally, a larger cloud of smoke is released at the rear during the kick-down, otherwise, there are no major issues with the handling. An upgrade with a larger engine would be impractical due to the need to remove the existing engine (V8 TDI Quattro - no thanks).

Due to the significantly decreasing annual mileage, the current state is perfectly adequate.

Greetings
Guste

One could also adjust the VTG control so that, during partial operation, the entire adjustment range is traversed more frequently.

Hi, Rainer

dieselschrauber wrote:

One could also modify the VTG control so that the entire adjustment range is traversed more frequently during partial load operation.

Hi Rainer,

Unfortunately, my knowledge of software ends much earlier than I would feel comfortable using it. Furthermore, this device also has master and slave STGs, which will likely need to be modified as well, etc.

If you say that the corresponding maneuver takes only five minutes, then of course we would be happy to revisit the idea. But overall, my father is happy and would therefore certainly not want to invest too much money, or put in too much effort.

Greetings
Guste

Optican and MPPS would be available

guste100 wrote:

A major engine upgrade is ruled out due to the need to remove the engine (V8 TDI Quattro - no thanks)

If you've done this a few times and know where to go, the whole process will take about 1.5 days.

Actually, a nice job.

By the way, I also have a new right turbo lying around here!

The engine unfortunately failed after a turbocharger issue.
The customer continued driving for approximately 50 km, and the engine died due to overheating caused by excessive oil in the combustion chamber (sucked in!).

I've never seen anything like this before; the piston has been torn multiple times, and there are parts at the top that seem to be permanently welded together. With great effort, it was possible to separate the piston piece from its head!