AFN: Troubleshooting Performance Issues & Fail-Safe Mode

Hello everyone,

..Again, the recurring issue of performance degradation with AFN, etc.
I've been reading this forum for quite some time now, and I've also been able to solve some smaller problems using the search function.
Now I'm going to share my limited knowledge, but I can't go any further .

"The problem I'm experiencing is a loss of power across the entire RPM range (although it seems less severe at higher RPMs)."
The problem has been going on for a while, and I had almost come to terms with it!
Until recently, the vehicle inspection (HU/AU) was due.
The mechanic warmed up my car for the emissions test and was totally disappointed with its performance (he drives an AFN himself).
He advised me to replace the mass airflow sensor, but that didn't solve the problem.
In addition, the MSG (presumably a piece of equipment) goes into emergency mode at full load, just above 4000 RPM.

So far, I have tried:

New LLM - no difference.
AGR deactivated (with plate) - no difference.
Resistance at N75 measured - values are within VW specifications. Voltage at the supply line measured - values are within VW specifications.
VTG rod - moves (tested with a syringe).
Diesel line - bubble-free.
Diesel filter - will be replaced this week.
Cat - will be checked this week.

Error memory:

00575 - Intake manifold pressure.
17-00 - Rule difference.

00542 - Needle feed mechanism.
30-10 - Interruption / Short circuit after positive terminal - Sporadically (This error was only recorded once and was not present at other reading times).


Today I drove the vehicle with log numbers 3/8/11, and during the second log, it went into emergency mode again.

My vehicle is a Passat Variant manufactured in July 1996, with an AFN engine.

Maybe someone has the time and could take a look at the two logs.
I converted the files to Excel format, but I can't create a proper chart. I don't know anything about this program :-/.

I would be very grateful for your help!

Greetings!!

Steffen.


Here are the two logs:
Log_01.xls
Log_02.xls

In the first log, your boost pressure is not being reached, and in the second log, the boost pressure is being exceeded, which puts the engine into a limp mode!

Is the VTG (Variable Transmission Gear) truly easy to operate, and is the end position reliably reached?
If applicable: Check/replace N 75!

Hello Steffen,

The amount of fuel injected is apparently limited in the second log by the 'turbidity-KF' value (the last value in module 8, which is a consequence of insufficient intake or measured air mass).
Typically, the mass airflow sensor (MAF) is defective in this case!

Did you really use a NEW and ORIGINAL mass airflow sensor, or did you take advantage of some cheap, low-quality offer?

Have you ever changed the air filter, or did you perhaps hide a cleaning cloth inside the air filter ??

A question for the experts:
The LD is being reduced in the second log via the TV. Is this also a consequence of the low measured air mass, or is the low air mass a consequence of that ?

Sincerely,
K. Oldewurtel

Okay, in the Log_01.xls file, the boost pressure is too high. However, it's not high enough to trigger an emergency mode.
He swings quite a bit over and then under.
In the Log_02.xls file, the LD (likely referring to a specific parameter or value) is not building up sufficiently, which causes the system to enter emergency mode.

You can tell when the emergency broadcast system is activated because the TV will switch to 94%.

I would say the VTG (variable turbo geometry) is sticking or malfunctioning, or it might be due to the N75 valve.
-> Set the MWB to the default setting 11 and observe its movement.

Quote:

The amount of fuel injected is apparently limited in the second log by the opacity sensor (the last value in MWB 8, which is a consequence of the insufficient amount of air being drawn in or measured). Typically, the LMM is then defective!

The air mass is so low because there is no LD present.

Quote:

The LD will be reduced in the second log via the TV.

No, small TV = VTG. "Zu" means "more pressure." He's trying to increase the boost pressure because it's lower than the target value... until the emergency mode shuts it down.

Quote:

Is that also a consequence of the low measured air mass

?

The air mass value in the MSG (presumably referring to a specific system or device) does not affect the boost pressure regulator.

Hello Malte1408,


'Zitat:' translates to 'Quote:' in English.
The LD will be reduced in the second log via the TV.

No, small TV = VTG. 'Zu' means 'more pressure.' He's trying to increase the boost pressure because it's lower than the target value... until the emergency mode shuts it down.

In the second log (Log_02.xls, rows 12...1, the LD is indeed reduced via the TV (92.4%). The quantity limitation is determined by the turbidity characteristic curve (lowest value). Am I making a mistake here?


The air mass value as a parameter in the MSG does not affect the boost pressure regulator.

Thank you for the information !


Could it be that two defects are occurring simultaneously?
- Malfunctioning VTG/LD control due to overshooting.
- Defective/incorrect mass airflow sensor (MAF sensor) due to quantity limitations imposed by the opacity characteristic curve.

BTW: Checking the N75 valve with a multimeter is definitely not the whole story. It can be internally clogged or stuck. The best approach is to temporarily replace it (yes, I know, that part costs about 80 euros...).

Best regards, Kassen.

Quote:

In the second log file (Log_02.xls, lines 12...1, the LD (light intensity) is reduced via the TV (transmission value) to 92.4%. The quantity limitation is determined by the turbidity characteristic curve (lowest value). Am I making a mistake here?

Yes, 92.4% already indicates emergency mode. Before that, it tries to reach the desired LD value using a smaller TV.

The limitation based on the opacity curve is necessary. It can't achieve its full air mass potential when it's missing 400 mbar of boost pressure...
Okay, the air masses indicated there seem to correspond to the boost pressure.
The LMM is not defective.

Even with a functioning Mass Air Flow Sensor (MAF), a TDI engine will run in a "limp home" mode until it has enough airflow, because the Long Term Fuel Trim (LTFT) needs time to adjust. That's the intended behavior.

Hello malte1408,

Thank you for the information !

Question: I'm looking for a general guideline regarding the relationship between air mass and boost pressure. Is there a rough rule of thumb for this (you mentioned that air mass and boost pressure are related)? Or is it based on empirical values?

Best regards, Kassen.

Hello!

Thank you for the many contributions .

Quote:

Did you really use a NEW and ORIGINAL mass airflow sensor, or did you take advantage of some cheap, low-quality offer?

Well, the LLM is already NEW...
However, it's from a well-known online auction site. The packaging says "Pierburg," and inside is an absolutely identical mass airflow sensor (MAF) from "i2s." Even the numbers match the original Pierburg part.

Quote:

Have you ever changed the air filter, or did you perhaps hide a cleaning cloth inside the air filter? icon_wink.gif

Air filter replaced!

This weekend, I will thoroughly check the VTG (valve train geometry) again for proper function and ease of movement.
Can the N75 valve be swapped with the EGR valve for testing purposes? (They look identical externally). If there's no other option, I'll have to bite the bullet and invest in a new one.


Thank you!

Steffen.

You can do it! That's what's so great .

Hi.

..Yesterday, I took another, closer look at the VTG.
The actuator/shaft was really stuck!!! I was 100% sure that it was working during the last inspection.
Apparently, there have always been occasional glitches in some area (which sometimes caused the system to go into emergency mode).
...and at some point, it just completely "froze up."
I didn't experience it quite as severely, as I only drove very cautiously after the initial performance losses caused by the emergency mode.

After removing the pressure chamber, I extensively examined the actuator lever ... now everything is working smoothly again.
After that, I immediately took it for a test drive and recorded two logs.
Now, there's a noticeable increase in performance, but I'm not entirely sure if that's all there is to it.
I immediately reinstalled the old Mass Air Flow (MAF) sensor after replacing it (since the new one didn't make any difference). Perhaps the new one might still offer some improvements now, or is the air mass reading okay?

Therefore, I would appreciate it if you could take another look at my two new logs.

And THANK YOU community!!! You have really helped me .

Logs:
Log_05
Log_06

The underbite is still quite pronounced.

Either the VTG (variable turbine geometry) needs a bit more adjustment, or check if you have enough vacuum.

It's also possible that there's a slight leak in the LL line, perhaps a crack or something similar, that only opens and releases air when pressure is applied.

The LMM is perfectly fine.