AFN Issues: Troubleshooting and Solutions

Hello, I know there are many articles about AFN in this forum, but none of them really address my specific problem.
I drive a 20-year-old Golf 3 TDI GTI with the AFN engine and a chip from Digitec.
"The problem doesn't always occur, but it's been happening more frequently lately. Usually, I notice it when starting the engine, as the MFA (Multi-Function Display) shows an average fuel consumption of more than 6 liters. Normally, I drive it around 5 liters. Then, when accelerating, the turbocharger pressure rises to 2.1 bar, and shortly after, it drops to 0.6 bar, and then slowly increases again. I thought it might be going into limp mode, but if that were the case, the pressure wouldn't start rising again, would it?"
I have replaced all the vacuum hoses.
I read the error codes, and it's showing me the following:

"One error found:"
00519 - Manifold pressure sensor (G71)
28-00 - Short circuit to positive.

I also read out measurement group 10.
1: 1155 mg/r
2: 979.2 mbar
3: 2142 millibars
100%

And yes, it also shows 2 bar on the boost pressure gauge.

Has anyone ever heard of this problem, or perhaps experienced it themselves?

Best regards, Paddy.
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paddy84 wrote:

Then, when accelerating, the boost pressure increases to 2.1 bar, and shortly thereafter it drops to 0.6 bar, and then it slowly increases again. I thought it might be going into limp mode, but if that were the case, it wouldn't start increasing again, would it?

That's right.

Quote:

1 error found: 00519 - Manifold pressure sensor (G71) 28-00 - Short circuit to positive

. Can the error be cleared?
When will he be back then? Sometime when you're driving at full speed again?

"Give us a MWB11 log with some of those LD over-torque and under-torque events, and a full-throttle acceleration in 3rd gear from approximately 1300 to 4500 rpm."

Quote:

I also read out measurement group 10. 1: 1155 mg/r 2: 979.2 mbar 3: 2142 millibars 100% and yes, it also shows 2 bar on the boost pressure gauge.

Do you perhaps have an absolute LDA? It should show about 1 bar at idle.

Hello,

Be careful, because the charger (presumably the original one?) can only withstand a pressure of 1.2 bar permanently. The pressure surges should normally only reach a maximum of 1.5 bar.

Have you checked the vacuum hose that runs to the MSG for any kinks or damage?

I can imagine that the pressure in the sensor within the MSG builds up slowly. As long as this is the case, the charger will be running at a higher level. Once the target pressure is reached, the regulation will continue slowly, because the pressure in the hose will cause it to expand, allowing the pressure to be transmitted correctly to the MSG.

Best regards, Daniel.

TDI-Daniel wrote:

I can imagine that the pressure in the sensor at the MSG builds up slowly.

For this to happen, the hose to the MSG on the engine side would have to have an extreme constriction (= principle of LDA damping), which I consider very unlikely.

I initially suspect a stuck VTG (Variable Turbine Geometry), which is further exacerbated by the increased soot buildup caused by the tuning. Significant control fluctuations are also typical in this case.

Hi, yes, the error can be cleared, but it reappears, just not always at full throttle, but at different times.

"Can you give us a MWB11 log with some of those LD over-torque and under-torque events, and a full-throttle acceleration in 3rd gear from approximately 1300 to 4500 rpm?"

Help me understand exactly what you want.

What's the LDA reading? My boost pressure gauge goes from a negative value to +2 bar.
"And I read out the measurement data group using VAG-COM."

"But it also makes a lot of black smoke when I accelerate fully. So, do you think I should have the VTG checked? Is there no way to test it somehow?"

paddy84 wrote:

"Please provide us with an MWB11 log that includes some of those LD over- and underswing events, and a full-throttle acceleration in 3rd gear from approximately 1300 to 4500 rpm. "???????" Help me understand exactly what you want.

Data from a VAGCOM diagnostic log.
Ich kann den Text nicht übersetzen, da ich keinen Text erhalten habe. Bitte gib mir den Text, den du übersetzt haben möchtest.

Quote:

Like a completely LDA? My boost pressure gauge goes from -something to +2 bar.

And does the needle already reach +2 bar? Then it's amazing that your turbo is still working.

Quote:

So, you think I should check the VTG? Is there no way to test it somehow?

Ideally, with a logging trip:!:.

Yes, the gauge is rising up to 2 bar on my LDA.
So, should I create a log file for my measurement block 11? If I understand correctly?

What is the probability that my boost pressure sensor in the MSG is defective?

Quote:

So, should I create a log file from my measurement block 11?

Yes, exactly.

Quote:

What is the probability that my boost pressure sensor in the MSG is defective?

It's likely going to zero because your LDA isn't connected to the sensor, and it's also showing a pressure that's too high, right?
I'm also leaning towards a faulty VTG sensor or a defective N75 valve, and that the displayed error is likely a consequence of that. The log file might provide more details.

Okay, I've created the log file. However, I just tried to convert it or save it with Excel, and it's not working!
Can anyone help me with this?

Okay, so I replaced the N75 today with a new one, but there's also one underneath it. Which one is the one causing my problem?
My boost pressure hasn't reached 2 bar yet today, and I haven't had any error codes, but the boost pressure still momentarily spikes to 1.5 bar.

As I mentioned, it would be great if someone could help me with the CSV files, and I think they could provide more information about them.

paddy84 wrote:

So, I created a log file. But I just tried to convert it or save it with Excel, and it simply won't work! Can someone help me with this?

Then, the best thing to do is to post the original .csv file in the upload forum. You're most likely to be able to get something useful out of it if it's not too corrupted.

Quote:

So, I replaced the N75 unit today with a new one, but there's also one underneath it. Which one is the relevant one for my problem?

The one from which a hose directly leads to the charge air cooler.

Okay, I posted it under "Golf TDI 1.9 AFN".
I think I'll take a picture of it to show you, because the two valves are connected.

Quote:

For this to be the case, the hose on the motor side of the MSG would have to have an extreme constriction (= the principle of LDA damping), which I find very unlikely.

It's possible. It depends on where the LDA is connected. It's already causing a problem.

Best regards, Daniel.

So, the pressure gauge is connected to the pressure pipe.
In the upper pressure pipe, there is a temperature sensor, and behind it, a vacuum hose runs into the pressure pipe, where there is a T-connector for the LDA (Laser Doppler Anemometry).
Has something already gone wrong here?

Think less, only if you've created a bend in the hose from the T-piece to the MSG, then you'll experience this behavior. Or the pressure sensor is faulty. 2 bar probably aren't doing it any good either.

Best regards, Daniel.

Okay, so the hose where I have the T-connector goes to the MSG?
Could it be that even if my LDA (Liquid Display Assembly) were faulty, this problem would still occur?