A4 TDI Intermittent Power Loss, AFN Engine

Hi,

"Recently, I've been experiencing occasional power loss during acceleration, particularly noticeable between 2000 and 3000 RPM."
(a4 B5, 110hp TDI, AFN - everything is still original)

Here's what's happening quite suddenly:

Waste charge pressure.
Waste EGR 0%.
Waste air mass.
Waste injection volume.
Waste Throttle (Gas?) -

(recorded using VAG COM)

As far as I can tell, everything happens simultaneously, it lasts for about 1-2 seconds, and then it goes back to normal. The car runs up to its maximum speed, and there are no error codes.

Das wohl das Gas zurückgeht, ist komisch. war auf einer konst. Acceleration.

Mileage: 170,000 km

Does anyone have any ideas?


Sure, here is the translation of the text from German to English:

"Hello"

tbkaudia4 wrote:

Hi, "I've recently been experiencing occasional power loss during acceleration, particularly noticeable between 2000 and 3000 RPM." (a4 B5, 110hp TDI, AFN - everything is still original) Here's what's happening quite suddenly: Waste charge pressure. Waste EGR 0%. Waste air mass. Waste injection volume. Waste Throttle (Gas?) - (recorded using VAG COM) As far as I can tell, everything happens simultaneously, it lasts for about 1-2 seconds, and then it goes back to normal. The car runs up to its maximum speed, and there are no error codes. Das wohl das Gas zurückgeht, ist komisch. war auf einer konst. Acceleration. Mileage: 170,000 km Does anyone have any ideas? greeting

Hi,

In the log https://community.dieselschrauber.org/en/viewtopic.php?t=14929 (which is useful if the questioner immediately posts the link ), the gas reaches a maximum of 90.6%.
However, achieving an acceleration of approximately 1300 to 4300 rpm is a prerequisite for a reliable diagnosis.
Okay, let's address the root causes first.
Does "gentle engine operation" mean not using full throttle?
Is there a floor mat or similar item under the pedal?
Is it a wiring issue near the pedal, or is the sensor defective? Are they accessible when the vehicle is stationary (engine off)?

Hi, I've created a new log, and I've done several full-throttle runs from 1500 to 4500. There are no noticeable misfires, but there are some visible anomalies when looking at the graph.

The turbocharger's boost pressure at 5000 RPM is approximately 1300 mbar at idle.

Can you make better use of it?

(of course, no mistakes)

Log: https://community.dieselschrauber.org/en/viewtopic.php?t=14929


Thank you again - also for the quick response.

tbkaudia4 wrote:

Hi, I've created a new log, with several full-throttle runs from 1500 to 4500. There are no noticeable misfires, but some are visible graphically. The turbocharger's boost pressure at 5000 RPM is approximately 1300 mbar at idle. Can you do more with that?

Yes, I've noticed that the load current (LD) never reaches the target value, even though the duty cycle is set to a high value ("giving it a lot of gas").
Not enough vacuum? Are the hoses leaking (especially the thick pressure and control hoses)? Is the solenoid valve defective?

Hi, thanks a lot.

I'll check that in daylight. The hoses are still the originals - so they're 9 years old. I can't see anything obvious. Do you think the vacuum test with a syringe is sufficient, or do we need to be more precise?

Greetings from Germany!

tbkaudia4 wrote:

Do you think the intake test with a syringe is sufficient, or does it need to be more precise?

For a rough check of the VTG-mechanics , a syringe is sufficient.
If the VTG mechanics are functioning correctly, I would next measure the pressure reaching the turbocharger housing at idle using a vacuum-based lambda sensor (refer to the technical documentation on the function and adjustment of VTG turbochargers for more details).
Then, depending on the results, continue searching...

You can only say that the service is top-notch and prompt...
It's a shame that I'm ranked lower, otherwise I would have given you a big plus .

Hi, everything's clear.

The small leak that was causing the problem was a crack in the sealing gasket between the intake manifold and the intercooler piping.

The crack developed during the test drives and eventually started leaking oil.

Despite this, I have a few questions.

Is the logged engine performance data okay? I had the boost pressure peaking at 2350 mbar, but otherwise, the pressure is regulated down to around 2000 mbar at full load. Does this seem okay? I would appreciate a final confirmation.

Secondly, shouldn't the significantly lower boost pressure trigger an error – specifically, a boost pressure regulation error? I never received any error messages.

Thank you to all F-members.

The log, which hopefully is okay: https://community.dieselschrauber.org/en/viewtopic.php?t=14929


Best regards, Frank.

tbkaudia4 wrote:

Is the logged engine performance data okay? I had the boost pressure at the peak up to 2350 mbar, otherwise the pressure is regulated down to approximately 2000 mbar at full load. It seems okay, right? I would appreciate a final feedback.

The misfire occurs mostly (slightly) below the maximum engine speed when running at full throttle. This should not be normal.
LuFi dicht? Kat verstopft? Is the LMM depleted?

Quote:

Secondly: Shouldn't the significantly lower boost pressure trigger an error - specifically, a boost pressure regulation error? I never received any error messages.

It depends on the error threshold in the MSG software.

Hi Ulf, thanks again for your prompt reply.

Is the Wi-Fi down? Is it new?

Is your cat constipated? Do you have any tips on how to tell, or how to fix it?

LMM (likely referring to a Lambda sensor) failed? - Possibly, I don't have a replacement. How else can I test it?

"Thank you. However, you hardly notice the limitations, so they don't really represent a restriction. If there's any indication of an LMM defect, I would arrange for a replacement."

Thank you again.

Frank.

tbkaudia4 wrote:

Is your cat constipated? Do you have any tips on how to tell - or what to do

?
Try searching here.

Quote:

LMM worn out? - Possibly, I don't have a replacement. How else to test it?

Look for "air leaks" between the mass airflow sensor (MAF) and the compressor. Otherwise, clean the MAF sensor (-> search / technical articles) or replace it.

Hi, I've replaced the LMM (mass airflow sensor), checked the catalytic converter, and replaced the hoses (after 9 years).

Everything is running smoothly. Now, the torque limitation is occurring before the oxygen sensor reaches its limit – so it was the mass airflow sensor (MAF).

Thank you all.

ulf wrote:

tbkaudia4 wrote: Is your cat constipated? Do you have a tip on how to tell - or fix it? Try searching here. Quote: LMM worn out? - Possibly, I don't have a replacement. How else to test it? Look for "

false air leaks" between the mass airflow sensor (MAF) and the compressor. Otherwise, clean the MAF sensor (-> search / technical articles) or replace it. }