G4 TDI AJM: Low Power? Troubleshooting Guide

Hello everyone,

Unfortunately, I have the feeling that my recently purchased G4 GTI TDI isn't running as well as it should.

The engine's responsiveness is generally okay, and the low-end torque is decent. However, above 3000 RPM, the engine feels restricted, although not abruptly. As mentioned, it performs well below 2000 RPM and then seems to gradually lose power. In my opinion, it becomes quite sluggish when trying to overtake another car on the highway at 90 km/h.

I've been reading a lot lately, and next weekend I'm definitely planning a major service for the car, as it's due. This will include a new air filter, diesel filter, pollen filter, oil filter, and new oil.

Today I also used the VAG-COM and logged some data. Based on what I've read here, I think the mass airflow sensor (MAF) is okay. I logged measuring blocks 3.8 and 11.

Next week, when we're working on customer service issues, I'm also going to disable or block the AGR valve. It made a significant difference for my girlfriend's 3er TDI 1Z.

I'm attaching the log file, maybe you can make more sense of it than I can , and perhaps you can make some educated guesses about which direction the error might be coming from.

Danke u. Regards,
Street Rod.

Today, I also used the VAG-COM and logged some data. Based on what I've read here, I think the MAF sensor is okay. I logged measuring blocks 3.8 and 11.

Hello.

Then, please take a closer look at the log, specifically the section from the beginning up to 50 seconds.

In the higher RPM ranges, the lambda value doesn't look very good anymore, which is a typical sign of an aging mass airflow sensor.
You are reaching your LM target (MWB003), therefore you are limiting the engine speed to over 3000 rpm using the smoke limiter.
The LD (likely referring to a load or pressure value) does not reach its target value because, during the acceleration phase, the IMA (likely referring to an integrated motor control system) uses the pre-control function to drive the main part of the VTG (Variable Geometry Turbine) control, and this control cannot adjust to the target value with the lower exhaust volume.
If the regulation allows enough time for adjustment, you will achieve the target level of performance.

Okay, let's check the LLM...

Best regards, Jochen.

Hey, thanks a lot, that actually sounds pretty good. I was secretly hoping for the LMM, but I think the financial aspect will be the smallest problem.

Could someone perhaps explain to me which specific values in which Measurement Work Breakdown Structure (MWB) I need to check in order to verify the functionality of the LMM (Likelihood Maximization Method)? I think I've been too focused on the 850 value that is almost always achieved.

Should I create another log? Maybe with MWB 10 instead of 11?

Greetings.

Hello,
IMA is sufficient with the log data.
Okay, I've identified a vulnerability that needs to be checked.


I probably focused too much on the almost always achieved score of 850.

Then, take a closer look at the MWB description.

For the air mass, there is a target value and an actual value (and the same applies to the LD).
The setpoint is the desired value that one wants to achieve. The actual value is the measured value. The control system always attempts to eliminate the difference between the setpoint and the actual value.
If she doesn't achieve that in the medium term, something is wrong.

During acceleration, the LM does not reach the expected 850 mg/h at high speeds.

Best regards, Jochen.

Hi everyone,

Since this issue has been bothering me, I tried cleaning the mass airflow sensor today and also tapped out the air filter, although it's going to be replaced next Saturday anyway.

Unfortunately, I couldn't observe any performance improvements. I also recorded two more logs, perhaps some experts could take a look; that would be great! However, I should mention that the car was occupied by 4 people, but even so, the values should still be within a reasonable range.

The first log showed a mean wind speed (MWB) of 3.8, 11, with one reading taken in 3rd gear and another in 5th gear. I tried to only record the acceleration phases. The second log also showed readings in 3rd and 5th gear, but with a mean wind speed of 3.10, 11.

Danke u. Regards,
Daniel.

PS @Jochen: I just looked at your Seat pictures earlier, are you not planning to get rid of your rims? I'm actually looking for exactly those right now...

EDIT: The first one didn't turn out so well, sorry.

Okay everyone, major service completed. New oil, new oil filter, new air filter, new diesel filter, and so on...

Unfortunately, no difference could be determined .

Could someone possibly provide some insights into my last two log entries? Specifically, I'm interested in information regarding air masses or any other unusual observations.

Maybe I'm just imagining all of this, and perhaps only a chip can provide a solution?

Danke u. Regards,
Street.

Hi Street,

Please upload the VAG-COM log files as they are, without any further modifications. The last two log entries seem to be merged.
Simply check if the fuel injection quantity value in field 4 of measurement block 8 is greater than the value in field 3. It should be higher when the accelerator is fully pressed.

Best regards, Rainer.

Hi everyone,

Unfortunately, I've had very little time these past few days, but yesterday I managed to create what I hope is a clean log; perhaps someone can take a look at it. Hopefully, it's not corrupted this time .
I also logged the data using the shareware software from KPower, and it shows 125 horsepower, which seems very high to me. As I said, I'm not really satisfied with the performance, especially since I put on 18-inch wheels yesterday, which makes it even worse.

Thanks in advance, and best regards.
Daniel.

Hello,

The 125 hp is the peak value of the curve, meaning it's the highest point on the graph, and corresponds to the "Zappler" setting on the clutch, which is located furthest to the right. This setting can be considered negligible.
Take a look at the torque curve, which starts to drop off around 3200 rpm, and the corresponding point on the measurement graph where the limitation due to air mass falls below the torque limit.

Obenraus fehlen aufgrund vermutlich defektem LMM etwa 2mg/Hub Einspritzmenge. Not much.

Best regards, Rainer.

Okay, sounds good.

I was almost certain of it; this time, it was also quite obvious from the logs that something was wrong with the LMM. I just wanted to hear an expert opinion on it.

Okay, I'll replace them sometime this week and let you know how it goes!

Danke u. Regards,
Daniel.

Hi everyone,

I'm writing again after a long time about my (still existing) performance issue.

I actually replaced the LMM a while ago, after my last post, but it didn't really make a difference, at least not anything noticeable.

A few weeks ago, I took off the intake manifold with my VAG buddy to see if that was the source of the problem. As expected, there was some black oil sludge present, but not to the extent shown in the example pictures on this forum. Anyway, I cleaned everything thoroughly and also sealed the EGR valve at the same time.

Unfortunately, neither of them resulted in any performance improvement .

Can anyone give me more tips on what else to look for? My acquaintance rules out a misaligned timing belt, as he says it wouldn't run properly at all. This issue appears late, at 9,000 km, so the new belt needs to be replaced. I've also read something about a fuel temperature sensor. Where is it located, or is it worth checking?
Okay, I'm also almost ruling out the KAT (catalytic converter), at least it doesn't rattle when you tap on it. By the way, the VTG (variable turbine geometry) adjustment is also common and doesn't get stuck!

Thank you very much, and greetings from Bavaria.
Street Rod.

Do the maximum target values for driver preference and target LD actually match?
The log shows 59 and 2091, but the database shows 55 and 2150.

Best regards, Klaus.

Hmmm...

Please let me know which channels I should run another logging session on, so I can upload the converted logs again. Hopefully, we'll see some changes due to the new LMM.

EDIT:
I quickly did three acceleration tests, flooring it in 4th gear as much as possible... well, as much as one can say.


Thanks and greetings.
Street.

PLEASE HELP

There's absolutely no need to convert anything in the logs.

Upload it as instructed by VCDS/VAG-COM.

Okay, so here are the logs again, as they are output by VAG-COM.