Turbocharger Boost Control AJM: The Next Generation

Hello fellow DIY enthusiasts,

My Bora has never really stood out for its exceptionally good responsiveness from the beginning.
/viewtopic.php?t=8225

One cause is the generally poor boost pressure regulation, which, depending on its mood, exhibits large overshoots and undershoots in boost pressure.
The immersion in the smoke barrier hinders the gas intake.

For Christmas, I followed the tip from the forum and, just to be on the safe side, had the boost pressure control valve replaced. Unfortunately, that didn't change anything.
But at least now I can safely rule out the N75 as a cause.

My Bora now has almost 110,000 kilometers on the odometer, and recently, when it's been cold...
The handling remained even worse, even after a brief full-throttle run in fourth gear.
Typical log files continue to show the usual patterns.
Sawtooth pattern of the actual charging pressure curve.

The annoying thing about this isn't just that the engine doesn't respond well when accelerating from low RPM.
It feels like it doesn't get any better from a performance perspective at higher RPMs.

This time, I logged some driving tests performed in group 011, as is typical.
'Constantly accelerating and decelerating every 2 seconds, then suddenly flooring it from a moderate speed.'
Low speed and light load, which is typical at the beginning of an overtaking maneuver.

I have VAG-Scope screenshots of some key points.
Periodic gas injection after a runaway reaction test.
http://members.aon.at/835935/060128/011_x2/011_periodisches%20Gasgeben%20nach%20einem%20Freibrennversuch.gif

011_Extreme peaks at moderate throttle input.
http://members.aon.at/835935/060128/011_x2/011_extremeSpitzen%20bei%20mittellangem%20Gasgeben.gif

011_Digital full throttle at 4000 rpm.
http://members.aon.at/835935/060128/011_x2/011_dititales%20Vollgas%20bei%204000umin.gif

I think the middle picture best shows what's annoying about the current state.
Regardless of the engine speed, especially when you want to accelerate suddenly, it starts...
Trying to find a way around the rules.

Meanwhile, I used the digital camera to photograph the charger and read the information from the pixelated label:
Charger:
[VW Emblem] VNT 15 Made in Italy.
038253019A GS4
454232-4 S/N DAI 0918

Vintage tin:
AlliedSignal.

My question to you experts:

Would a wheel loader be useful?
Is the loader responsible for the overshooting and undershooting, or could it also be related to that?
that the boost pressure control strategy in my engine control unit is from the very first PD series (038 906 019 AM).
Perhaps it's worse than in later models – in other words, are you suggesting that I should have the charger and battery replaced?

If I have the charger repaired or replaced: Is there a more modern subtype of the VNT 15?
Which one fits, and what (number, addition, external feature) can I use to identify it?

What should I pay attention to when buying the product in a can? Are there different versions or manufacturers?


Best regards,
Herwig.

Hello Herwig,

If the air hose connected to the VTG control valve is in good condition and not blocked, then the problem is likely either with the VTG mechanism itself or with the vacuum cylinder.
You can unscrew the canister from the loader; then you'll be able to move the adjustment lever along with the canister.
That should be really easy to do.
If the vacuum sensor is stuck or "glued" and you find a suitable replacement, please let me know; unfortunately, I haven't been able to find a source for it.

In both cases, the only likely solution to ensure nothing remains attached afterward is probably using a specialized exchange unit.
You can then disassemble and inspect the old loader at your leisure, without feeling rushed.

Best regards, Rainer.

Hello Herwig,

If the vacuum hose connected to the VTG control valve is in good condition and not blocked, then the problem is likely either with the VTG mechanism itself or with the vacuum actuator.
You can unscrew the canister from the loader; then you'll be able to move the adjustment lever along with the canister.
That should be really easy to do.
If the vacuum sensor is stuck or 'glued' and you find a suitable replacement, please let me know; unfortunately, I haven't been able to find a source for it.

In both cases, the only likely solution to ensure nothing remains attached afterward is probably using a specialized exchange unit.
You can then disassemble and inspect the old loader at your leisure, without feeling rushed.

Greetings, Rainer.

Hello Rainer,

I was afraid of that; it seems only replacing the cartridges and dispensing units will really help.
I've already come to terms with it. Unfortunately, it seems there really aren't any replacement units available.
I'm willing to provide more information, but I was also told that the cans are only available with chargers. I find the argument about the rod length ridiculous because anyone who has a VAG-COM and has seen logs of both too long and too short rods can, with some patience, find the correct length.

I was also curious if any forum members had experience with a wheel loader – ideally with an AJM model.
Specifically interesting would be: How well does the charging regulation work after the charger replacement, and how long does it take for everything to return to normal...?

It might be around Easter time when I have my timing belt replaced that I will also get the loader replaced.
I will definitely create logs and share them.

Best regards, Herwig.

Hello Herwig,
Take a look at some of my older responses.
I went into quite some detail about the procedure for setting up the tax software.
In summary: The VTG/VNT valve must be at -600 ±20 mbar when measured at the adjustment screw (minimum position / VTG closed). This can be easily checked and adjusted using a simple hand vacuum pump and (accurate) pressure gauge. The time required is approximately 15 minutes if you are experienced and everything is in good working order.

Regards,
Dirk.

Hello Herwig,
Take a look at some of my older responses.
I went into quite some detail about the procedure for setting up the tax software.
In summary: The VTG/VNT valve must be at -600 ±20 mbar when adjusted to the minimum position (VTG closed) at the adjustment screw. This can be easily checked and adjusted using a hand vacuum pump and (accurate) pressure gauge. The time required is approximately 15 minutes if you are experienced and everything is in good working order.

Regards,
Dirk.

Thanks, Dirk, for the tip. I'll need to look into getting a pressure gauge first, but it definitely seems worthwhile.
also auch for checking a new can.

So far, I've only performed the actuator test for the loader, where the MSG (Motor Steuergerät - Motor Control Unit) keeps the engine at a constant 1400 RPM and opens and closes the valve. This resulted in a pressure difference of approximately 110 mbar, which is quite low. However, I believe that the VTG (Variable Turbine Geometry) is closing correctly, at least when it's under full vacuum.
I'll post something as soon as I have some measurements.

Regards,
Herwig.

Hello herwigw,

Nothing has changed for you, and nothing has changed for me either.
My boost pressure logs are identical to yours. I even swapped the EPW just for fun, but that didn't change anything either. I've also tried all possible settings on the wastegate, eliminated all potential sources of error (including disassembling and cleaning the turbocharger - trying different vacuum canisters), and checked everything, and like before, I'm still at the same conclusion:
The control device of the VTG wagon has failed; therefore, the ATL (Air Load Valve) needs to be replaced to ensure proper regulation.
"However, since I don't notice any significant handling deficiencies (those fractions of a second in the smoke test for low-drag understeer are barely noticeable), I refuse to have them replaced – they might only have a positive effect on the measurements."

If you do end up changing the ATL, I'd be very interested to hear about your experience.

Best regards,

Hello herwigw,

Nothing has changed for you, and nothing has changed for me either.
My boost pressure logs match yours exactly. I even swapped out the EPW just for fun, but that didn't change anything either. I've also tried all possible settings on the wastegate, eliminated all potential sources of error (including disassembling and cleaning the turbocharger - trying different vacuum canisters), and checked everything, and like before, I'm still at the same conclusion:
The control device of the VTG wagon has failed; therefore, the ATL (Air Load Valve) needs to be replaced to ensure proper regulation.
'However, since I don't notice any significant handling deficiencies (those fractions of a second in the smoke test for low-drag understeer are barely noticeable), I refuse to have them replaced – they might only have a positive effect on the measurements.'

If you do end up changing the ATL, I'd be very interested to hear about your experience.

Greetings.

Hello Bavarian.

I'm sorry to hear that your AJM is experiencing similar problems.
It's always a very personal matter whether someone is bothered by one flaw or another. The 'start-up rattle' really bothers me! Whenever you're in a hurry and press the accelerator, you usually just get a sputtering sound. But there are days when the low-frequency vibrations almost disappear completely, and you can feel that it could be different: namely, an immediate surge of power and about a second more. When I think back to my old gasoline-powered Passat, with its reassuring reliability that always responded smoothly to the accelerator pedal in any outside temperature, I'd almost like to have this Bora scrapped.
It's especially frustrating when driving in city traffic and there are only brief openings for lane changes, or if you have to quickly move out of the way because you almost hit someone.

What I'm really curious about is whether the charger is actually to blame for the poor regulation of the AJMs. My 011 logs also show the control strategy of the MSGs. It seems too slow to me, but I have to admit that I don't understand any of it. It would be stupid if I replaced the charger and then found out that it wasn't the problem at all.

Do you actually have the exact same charger? Could you check the number? Apparently, some chargers have subtypes, but I don't know if that applies to our AJMS models and what improvements might have been made.

Best regards,
Herwig.

An interesting post that is also relevant to this thread.
Okay, I'm ready. Please provide the German text you want me to translate into English.

Best regards, Ulf.