Boost Pressure Drop AFN 81kW

Hello everyone,

After searching through all the posts for clues and trying all the suggestions for three days, I'm now reaching out to you directly.

We are experiencing the following problem with our Seat:

Full acceleration: at approximately 2450 RPM, the boost pressure drops from 2350 mbar to 1600 mbar. Then, the boost pressure slowly increases again.
When the accelerator pedal is released and then pressed again, the pressure spontaneously rises back to 2350 mbar (approximately 2 seconds) and the system is throttled back again. This occurs consistently above 2450 RPM. (Measured by the workshop in my presence).

The following can be ruled out:
Air mass sensor replaced, vacuum system OK, VTG adjustment mechanism free, solenoid valve for VTG adjustment replaced.
I once measured the voltage at the VTG (Variable Train Heating) magnetic valve myself:
'At 2450 RPM, this value drops spontaneously from approximately 6V to 3V. Otherwise, it fluctuates between 10V and 4V.'

The workshop wants to replace the loader for me next.

Does anyone have any other ideas for limiting the scope of the issue?

Thank you very much.

Best regards, Olaf.

Hello,

Did you have the error codes read? If so, what were the entries?
Have you perhaps also had the measurement data blocks read out (a list is available in the error database)? If you also have values here, please just post them.

Hello,

Did you have the error codes read? If so, what were the entries?
Have you perhaps also had the measurement data blocks read out (a list is available in the error database)? If you also have values here, please just post them.

Hello Michael II,

According to the workshop, there are no errors stored in the system's memory. However, I will double-check that.

Best regards, Olaf.

Hello,

During my AHF (Acute Heart Failure) episode, the behavior was identical. The VTG (Ventricular Tachycardia Generator) was getting stuck in certain positions.
I didn't enjoy the new loader that was given to me for free; it broke down on me after a short period of full-throttle use.
Looking back, I would probably lean towards repairing it, even though a new charger for €0 sounds tempting, for the following reasons:
- Is the new charger okay? In my case, the shaft broke after just 500 meters of full throttle -> That's not good for the engine if it starts sucking up debris/shavings. Mine seems to have survived it, but not well.
- Is the workshop okay? When replacing the turbocharger, a lot of things can go wrong. In my case, for example, the intercooler pipes were attached so poorly that they would eventually have come loose, and the next damage would have been inevitable.
- Never change a running system.
- Ulf got a larger canister for the VTG adjustment (more adjustment force). Possibly, your adjustment canister is also leaky/jammed in certain positions. It's easy to check because the canister is only attached to the turbocharger with 2 screws. Lubricate the VTG joint and adjustment shaft well with copper anti-seize paste.

Best regards, Rainer.

Alhambra01 wrote:

Full acceleration: at approximately 2450 RPM, the boost pressure drops from 2350 mbar to 1600 mbar. Subsequently, the boost pressure slowly increases again. When the accelerator pedal is released and then pressed again, the pressure spontaneously rises back to 2350 mbar (approximately 2 seconds) and the system is throttled back again. This occurs consistently above 2450 RPM. (Measured by the workshop in my presence). The following can be ruled out: Air mass sensor replaced, vacuum system OK, VTG adjustment mechanism free, solenoid valve for VTG adjustment replaced. I once measured the voltage at the VTG (Variable Train Heating) magnetic valve myself: "At 2450 RPM, this value drops spontaneously from approximately 6V to 3V. Otherwise, it fluctuates between 10V and 4V."

Hi.

2.3 bar is quite a bit too much pressure; the engine computer will actively compensate for it (by reducing the voltage to the solenoid valve).

With a jerky VTG (which I also assume is the case with you, because it fits well ), the strongly steered cylinder will eventually adjust the loader beyond the resistance limit - and of course, in doing so, it will overshoot the target --> resulting in too little charging pressure.
The subsequent counter-correction to a higher pressure initially fails again due to the aforementioned clamping point in the VTG (variable geometry turbine) adjustment range. Instead, the pressure (with the VTG forced to a constant position) slowly increases again, similar to the rate, due to the gradually increasing engine speed...

Since you also have the AFN, I'm almost certain that it's a purely VTG-related issue.
Who (according to what criteria?) determined that the VTG is accessible?

"I haven't had any problems with the larger charging coil for several weeks now --> check the error database and the post about the stuck VTG."

Seat will likely try to sell you a new charger. I gather this from the responses I received regarding my VTG matter from the VW sales center in the Rhine-Main region.

Good evening, everyone.

First of all, thank you very much for the numerous responses.
I called the workshop first thing this morning: there were no error codes stored.
Okay, so tonight I'm once again lying under the car and removing the pressure sensor (7.5cm). The adjustment lever directly on the turbocharger housing can be moved freely in any position, but... the rod connecting the pressure sensor to the adjustment lever gets stuck in one position if it's not guided perfectly. Unfortunately, I can't reach the retaining clip to disassemble it. As you suggested, I lubricated the joint with copper grease, and it seems the pressure drop during driving is now less significant. In 3rd gear, it now revs up to almost 3000 RPM.
So, the whole problem must be this silly rod with too much play.
On Friday, I'm going to do a test drive with the trailer, and then I'll finally see if it made any difference.
Thank you again for your help.

Best regards, Olaf.

Alhambra01 wrote:

but... the rod connecting the pressure chamber to the adjustment lever hangs in one place if it is not guided exactly.

Hello, I experienced the same thing when I manually adjusted the VTG (Variable Transmission Geometry).
Since I was going to receive a new charger as a courtesy, I didn't investigate the cause of the malfunction further at the time. However, I suspect it was more likely the vacuum sensor, as if a spring inside had broken or become stuck.
If you unscrew the vacuum cylinder from the loader (do not unscrew the actuation rod; it is sufficient to loosen the 10mm nuts on the bracket), the VTG lever on the loader should move absolutely freely without any resistance.
-> Either purchase a new vacuum sensor, or have a new charger installed free of charge (as a goodwill gesture). Be careful: if your contribution is more than 100 euros, and the charger is otherwise okay (i.e., provides proper boost pressure, doesn't leak anywhere, and the oil consumption is normal), then buying a new vacuum sensor is cheaper.
When possibly replacing the vacuum sensor, ensure that the VTG rod is adjusted so that the rest position of the VTG lever is the same as before, and that approximately the same spring tension (~0N) is applied.
If the rod is adjusted too short, the control unit may no longer be able to sufficiently reduce the boost pressure. This puts the turbocharger and engine at risk, especially in cold weather and during full acceleration, which can more frequently trigger the limp-home mode.
If it's too long, you might experience sluggish engine response and potentially a loss of boost pressure, which can lead to a decrease in power.
Tip: Adjust the length so that, with at least 3 seconds of full throttle in 3rd, 4th, or 5th gear at 3900 RPM, the magnetic valve for boost pressure control achieves a duty cycle of approximately 85-90%. The duty cycle can be read out using a diagnostic tool. The maximum duty cycle is approximately 95%, but you should maintain a reserve of 5-10% because at temperatures below 0°C, boost pressure is more easily achieved, and the control unit needs to regulate it back more .

"I haven't had any errors stored in the system except for one occurrence every 5000 kilometers."

Best regards, Rainer.

Hello everyone,

Today was the day, the new turbo is installed...
'and the car is still running almost as badly as before. The pressure drop is still noticeable, and the cruise control can't maintain the speed even on the slightest incline. The workshop says they should replace the mass airflow sensor again (which, supposedly, was already done at the very beginning)... I'm starting to feel like I'm being ripped off.'
Let's see who's going to foot the bill now...

I will let you know if there are any updates.

Best regards, Olaf.

Hello,

I would suggest, in your place, that you have the measurement data blocks read out again (displayed in the error database). Have them printed out as well. This might help to narrow down the cause of the problem. Otherwise, they might end up replacing half of the engine.

Alhambra01 wrote:

Hello everyone, Today was the day, the new turbo is installed... "and the car is still running almost as badly as before. The pressure drop is still noticeable, and the cruise control can't maintain the speed even on the slightest incline. The workshop says they should replace the mass airflow sensor again (which, supposedly, was already done at the very beginning)... I'm starting to feel like I'm being ripped off." Let's see who's going to foot the bill now... I will let you know if there are any updates. Best regards, Olaf

My knife is popping open in my pocket... how about those incompetent idiots in your workshop just leave the mass airflow sensor (MAF) alone?
If I were in your shoes, I wouldn't have gone to them the last time, and I certainly wouldn't pay money for such ridiculous stunts .
Right at the beginning, you mentioned that the boost pressure exceeds 1.3 bar and then drops back to 0.6 bar. Before replacing the turbocharger, check the mass airflow sensor using diagnostic tools, and after replacing the turbocharger, a boost pressure measurement is definitely the minimum. Were you simply given the car back without any checks?
If the boost pressure cannot be regulated back down using a vacuum diaphragm, further investigation in that area is necessary.
What is the duty cycle of the solenoid valve when the boost pressure approaches 1.3 bar? As Michael already mentioned, it's time to read out the measurement blocks!
The cost of taxis and public transportation after my fourth visit to the repair shop had slowly started to equal the price of a diagnostic adapter, so you should also consider buying one.
If the vacuum hoses are not kinked or blocked, and the magnetic valve for charge pressure regulation is working correctly, check the venting of the vacuum system.
Somewhere, when the vacuum pressure decreases (and thus, the intended boost pressure is reduced), air must re-enter the boost pressure/vacuum system.

Okay, I just checked the vacuum hoses on my car. From the top of the air filter housing (next to the mass airflow sensor in my case), the vacuum relief hose goes to a T-connector and branches off to the upper port of the...
- Magnetic valves for turbocharger pressure control.
- and of the magnetic valve for controlling the exhaust gas recirculation.
It is very easy to determine which solenoid valve is responsible for what by tracing the vacuum hoses from the control unit on the turbocharger or the EGR valve.
To rule out a defect in the EGR solenoid valve (which might be constantly drawing in all available air, causing the vacuum at the turbocharger to persist), remove the T-piece and connect the hose directly from the air filter housing to the inlet of the solenoid valve for turbocharger pressure regulation. Blow into the hose to check if anything is blocked. Insert a fuel filter, for example, into the hose leading to the EGR solenoid valve to prevent dirt from being sucked in.
Now, park the car next to it, use the auxiliary function to start the engine, and let it idle.
Observe the adjustment lever on the VTG (Variable Turbine Geometry): when the engine is off, it should slide to one extreme position (the adjustment rod should be fully extended out of the vacuum actuator). When the engine is idling, the adjustment rod must be fully retracted into the vacuum actuator.
Machst Du nun den Motor wieder aus, muß die Verstellstange sofort (~1s) wieder in die Motor-Aus-Stellung flutschen. Let's test that first.

Best regards, Rainer.

To rule out a defect in the EGR solenoid valve (which might be constantly drawing in all available air, causing the vacuum at the turbocharger to remain), remove the T-piece and connect the hose from the air filter housing directly to the inlet of the solenoid valve for turbocharger pressure regulation. Blow into the hose to check if anything is blocked. Insert, for example, a fuel filter into the hose leading to the EGR solenoid valve to prevent dirt from being sucked in.


I just quickly checked that. I simply left the T-connector open to ensure the solenoid valve gets enough air. Nothing has changed.
Tomorrow, I'm going to have a performance test (Bosch service) done to finally get some readings. Then, on Tuesday, I'll have those data blocks read out.

Best regards, Olaf.

Hello everyone,

The box is working again.
After the air mass sensor was replaced for the second time on Wednesday, things are finally working properly again (maximum speed is back above 180, compared to only 150 before).
I will post the invoice details at a later date.

Thank you for your contributions.


Best regards, Olaf.

... is it finally getting better? I hope you have more luck with your new, free turbocharger than I did. If the repair holds up, you can be happy, because the parts aren't cheap, and a turbocharger doesn't last forever either.
Still, it's a bit weak of the workshop to cheerfully replace parts.
If I had added up the hours I spent dealing with the four visits to the workshop for my "4 + 1" (excavator-loader) machine, I could have probably repaired it myself.

Best regards, Rainer.

Hello everyone,

...
I will post the invoice details at a later date.

Thank you for your contributions.


Best regards, Olaf

And here is the invoice, as promised.
1390€, I just emailed Seat. Let's see how accommodating they are.


Best regards, Olaf.