Low Boost Pressure: Causes & Solutions

Hello screwheads!


Can someone explain to me why there's an entry in the attached log file for my Audi A3 1.9 TDI 110PS?
The turbocharger doesn't reach its full boost pressure until 2500 rpm, and produces far too little boost in the lower RPM range.

If I have a leak in the charge pressure system, then I can't possibly reach the maximum charge pressure, right?



Best regards,

Bertl.

Here is the raw, unanalyzed log.
I'm not very familiar with the English terminology.


Best regards.

Bertl.

Recently, there seem to be an increasing number of issues related to insufficient low-end torque at low engine speeds.
Therefore, I have added information to the FAQ about common mistakes.

If anyone can think of any other possible causes, please post them here or send me a private message.


It might also be interesting to consider basic settings for load diagnosis, where the load detector (LD) behavior at idle is analyzed by varying the VTG (variable turbine geometry) control.

Does anyone know which engines this applies to, and which it doesn't? Also, what values are supposed to be achieved?

Quote:

If I had or have a leak in the boost pressure system, then I wouldn't be able to reach the maximum boost pressure, right?

If the charger has enough reserve capacity at full pressure to compensate for the loss, then it will work fine (until the charger potentially fails prematurely).
Of course, this also depends on the size of the leak.

@Bertl,
You definitely have a defect in the charging system (the VTG seems to be closing almost not at all mechanically). As Ulf already mentioned, you should check all the possible causes listed in the technical article.

@Ulf,
As far as I know, all VTG-VAG diesel engines with an EDC15 or later engine control unit can have the basic ATL (air intake temperature learning) adjustment applied. I'm not sure about Wastegate and MSA12/15 systems.
The LD values achieved are insignificant (applies to the VTGs) and not comparable, as the boundary conditions between the concepts differ significantly (e.g., speed, load, ADF, aging). What is important is that the value changes (pressure difference) at the maximum/minimum TV setting, as this verifies the general function of the control system.
The LD (Load Detection) differential typically ranges between 20-50 mbar across all possible configurations (This is my experience with VAG VTGs - not a fixed rule).

Another point that might be interesting would be to determine the basic attitude of the ATLs.
For a specific type of TV (vacuum at the adjustment housing), the VTG should be completely closed (with the smallest possible flow diameter, where the stop forms the adjustment stop screw). If you determine the required vacuum using, for example, a VAG 1397A vacuum gauge and a vacuum pump, until the adjustment rod reaches the stop (definition of stop: a slight suction gap between the rod and the stop screw, measured with a 0.1mm feeler gauge), you obtain a wonderful reference value (as long as you don't tamper with the stop screw – which no one should really do, unless they have a flow testing stand). This is especially helpful if you have removed the adjustment housing or the rod is twisted in an undefined way. I'm almost certain that the same value will be obtained for all properly functioning VAG-VTGs. Is there not even a repair instruction for the V6 TDI? – And hopefully I haven't told any old tales; if so, sorry, I didn't search thoroughly enough.
Have fun experimenting!

@Ulf

Hi Ulf.

You are writing in a technical article -> The VTG is not adjusted to achieve the maximum charging pressure (e.g., due to a jammed VTG, incorrectly adjusted VTG stop, defective solenoid valve, defective, detached, or incorrectly connected vacuum hoses, defective vacuum pump) .

The reason for this could also be (at least in the case of the AXR engine) a damaged membrane in the pressure sensor for the exhaust cooler. Unfortunately, I don't know which other engine codes also have an exhaust cooler. However, I suspect it's not many. My mechanic certainly searched for a long time before he finally located the problem.
The pressure difference at the elevated idle speed (1400 rpm) with a functioning, fully engaged variable geometry turbocharger (VTG) was 150 mbar. With the defect, it was only 30 mbar.

Perhaps you could include this in the FAQ.

I also sent this to you as a private message...

Hati wrote:

Maybe you can still include this in the FAQ.

Yes, thank you, it will be done.

In this context, I am looking for a target value for the (minimum) vacuum pressure in the pneumatic system.

I mean, someone wrote about that somewhere here recently, but I'm probably using the wrong search terms?

With this value and a suction-type Linear Displacement Actuator (LDA), it would also be possible to perform some quick checks.

I found values for this in two places, but unfortunately, I don't have access to them right now.
1. In the service documents for Pierburg (N 75).
2. In the repair manual for the A3 100PS PD engine.

I'll check on that, but if someone else gets access to it sooner...

Holger247 wrote:

I found values for this in two places, but unfortunately, I don't have access to them right now: 1. In the service documents for Pierburg (N 75). 2. In the repair manual for the A3 100PS PD engine. I'll check on that, but if someone else gets access to it sooner...

Hi,

I've found some information from Pierburg: the EGR valve should have a minimum pressure of 450 mbar at idle.

The measured vacuum pressure in the AUY system is 700 mbar.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

From this, I estimate that the pneumatic system should have a pressure of at least approximately 500 mbar available.

I would also be interested in your research .

I have now run a new log file and imported the data into Excel accordingly.

Can you tell me what's wrong based on the values?
For me, this is difficult because several sensor values depend on each other.

It would be nice if someone would take me under their wing.


Best regards.

Bertl.

Bertl100 wrote:

I have now run a new LOG and imported the data into Excel accordingly.

. . . and everything that could be interpreted as a date has been converted into a date.

If you've just opened the .csv file, simply save it and choose "xls" as the file type, and you won't encounter this issue.

Quote:

It would be nice if someone would take care of me.

There's probably someone who can help if the log is readable -> please fix the date issue and upload the log again .

I've made it easier to understand now.

Bertl100 wrote:

I've made it more digestible now.

So far, so good .

However, in my opinion, the diagnosis (see above, e.g., from bafische) doesn't change for the time being.

Okay, please review the entire program according to the technical article, including the basic settings in the MWB 11 (see https://community.dieselschrauber.org/en/viewtopic.php?t=10428).).

Then we'll see.

I tried it, but in group 11, nothing happens when I press the "reset to default" button (no reaction, no new window).

I'm using an older version of VAGCOM, probably version 3.2 or something like that.

Bertl100 wrote:

I tried it, but in group 11, when I press the default settings button, nothing happens (no reaction, no new window). I am using an old version of VAGCOM --- 3.2 or something like that.

I'm also not up-to-date with VAGCOM... so either your control module (ECU) is too old (year of manufacture??), or your VAGCOM version might be a shareware version?

Whatever. The basic setting is actually just a way to make your work easier. Then you should just check the rest bit by bit.

I will do that, and THANK YOU for your help!


Best regards.


Bertl.

By the way, I just fixed our Ibiza, which was also having trouble building up boost at low engine speeds.

The trigger for this was that my wife mentioned that, sometimes, she felt like the car wasn't braking properly.
During a test run, I noticed that the pedal felt heavier than usual, similar to what it feels like when the battery is about half empty.

The cause was a hardened vacuum hose to the BKV (waste gas valve), which was already so torn at the hose connection (and only loosely attached) that it was drawing in a significant amount of "false air" -> Seat cheap junk .
As a result, the vacuum pump was only moving air, but hardly creating any vacuum. This is also why the LD (likely referring to a specific system or measurement) was weak.

Sometimes it's good to keep all sorts of junk instead of throwing it away.
A piece of tubing from a discarded washing machine fits perfectly as a replacement - and is already older than the Ibiza, so there is hardly any reason to fear that this thing will become brittle and eventually cause the same problems as the original part .
(which, incidentally, would have cost a mere 22 euros to replace as a complete unit between the pump and the BKV, because the torn hose piece is not available separately ).