VAG-COM Timing Check: TDI Error Troubleshooting

Hello everyone,

After suspecting that the injection timing might be incorrect on my AFN engine, I borrowed a full version of VAG-Com (including a laptop to avoid any questions).

Now, the timing checker reports that my injection timing is so late that it cannot even display it. The comparison between the actual and target injection timing (data logging) shows that the ESP (Electronic Stability Program) cannot compensate enough. At full throttle, there is a difference of 6-8 degrees. For the partial load range, it is still acceptable. Therefore, the conclusion is: the regulation is fundamentally okay, but the adjustment range is incorrect.

As far as I can tell, it's okay and makes sense to me.


Okay, I wanted to see how it was with a different car, so I borrowed a 2001 model with a 130hp PD engine, and lo and behold: the timing was so early that the diagnostic tool couldn't even display it. ?????????
Now, this is a company car that has been meticulously maintained in the workshop, is completely original and in good working order.
Now, of course, I no longer trust the VAG-Com display on my own car either.


Does anyone know what's going on? Are there known false readings from the VAG-COM system? Could something be wrong with the diagnostic tool itself?
What exactly does the (y-axis) of the VAG-Com display show? Surely it can't be degrees, given the values up to 80?

I have screenshots of the measurements, but I don't want to flood the forum with them. However, I'm happy to send them to anyone who's interested.

My car: A 12/98 A4, chipped with 110 horsepower, AFN engine, 160,000 km. Has a loss of power.
Vollgasrußen trotz 1,2 Bar Ladedruck bei verminderter Leistung. LMM and injectors replaced.

'I can borrow a VAG_COM, but I don't have any documentation for it. Does anyone have any VAG_COM documentation, or is it a closely guarded secret? I've searched the entire forum, but I haven't found anything.'

And finally, does anyone have a guide for replacing the timing belt on an A4 TDI, perhaps with tips on how to do it without having to disassemble half the car?
What working hours does VAG specify?

Greetings and thank you very much for the (hopefully) helpful assistance.
Sure, I'd be happy to translate the text from German to English. Please provide the text you would like me to translate.

You can also send it to [email protected] if you prefer.

Hello,

The interpretation of the values in VAG-Com depends on the specific measurement block being used.
In measurement block 0, simple numerical values are output, which can then be converted into actual measurement values.
When checking the injection timing, you only need to compare the numbers in the diagram.
In all other measurement blocks, the numbers have already been converted into measurement values.
The injection timing is calculated in degrees before top dead center (BTDC).

Best regards, Rainer.

@doc snyder

This happens because VCDS (VAG-COM) retrieves your measurement blocks sequentially. Since some time is required for data transfer, it's possible that it takes approximately 1 second to receive the values from the second group. Consequently, a difference in speed readings logically arises.

@garth.brooks

When you check the fuel injection timing, are you essentially already in diagnostic mode in VCDS (VAG-COM)?

Hello Doctor!

It's simply due to the serial transmission of the data.
VAG-COM operates with a specific sampling rate. When you read only one data block, these values are determined simultaneously. When logging multiple data blocks "simultaneously," the data acquisition is distributed over time; that is, the values for the first block are recorded first, then the values for the second block in the next sampling step, and so on.

Regards,
Alex.

joergs wrote:

@garth.brooks if you are checking the fuel injection timing, are you essentially already in the basic settings mode in VAG-COM ???!!!!!

Hello.

... I think so, because, as far as I know, the graphical TDI timing checker can only be accessed in the basic settings menu.

@ulf

You are absolutely right!

@jörg, alex

Thank you for your answers! That's more or less what I thought. Of course, that's not ideal. So, if I log multiple blocks, I get fewer values!?
There was a test in a thread like this where you were supposed to accelerate from idle (rolling) in 1st gear to 3000 RPM with a 1Z engine and log the whole process. I did that too. I actually wanted to post the values, but I ended up with only 3 lines in my log file.
I think my laptop is too slow! (P120,32MB) However, I've read that you can increase the transfer rate in VAG-COM. I guess I'll have to try that.

@doc snyder

Okay, I have a 486 with 4MB of RAM and I'm getting decent results! The sampling rate isn't huge, but it's sufficient! Are you experiencing any communication problems in the middle of the process?

Hello Doctor,

The sampling rate depends less on the laptop you are using and more on the characteristics of your interface and the specific control unit.
If you can achieve 3 measurements per second, that's already quite good.
Therefore, in my opinion, taking a measurement in the first gear is not very useful.

Best regards, Rainer.

Hello,
I have a question about the timing checker, so instead of starting a new thread, I'll just ask here briefly. (Hopefully that's okay.)

Okay, I took a Screenshot, but I don't know what to do with the values, or how to interpret them to see if they are good or bad.

[Image no longer available]

It would be nice if someone could clarify for me whether this is all okay, because I'm not understanding anything from the VAGCOM manual either.

I hope I'm not bothering you.