Boost Pressure: Slow Response Explained

Hi.

I've found a lot of information about the VTG turbocharger using the search function in this forum, but unfortunately, not much about the wastegate turbocharger. I have a motor with the code 'AGR'. Can someone explain how it differs from the VTG turbocharger? Or, could someone provide a link where I can find this information?

But now, let's get to my problem...

I just had my car scanned with VAG-COM, and unfortunately, my suspicion was confirmed:

The boost pressure lags significantly during pressure build-up... in my opinion, it's much too slow. It then rises 0.15 bar too high, drops to 0.1 bar too low, then rises a little too high again, drops back to the target pressure, and then rises a little again... while the target pressure is decreasing (around 3800 RPM). The overshoot of the boost pressure occurs at 2400 RPM.

While driving and fully accelerating, I'm also missing the boost that I usually have at 1900 RPM, but the maximum speed is not a problem.

Sometimes the engine also goes into limp mode... after restarting, it goes away --> intake manifold pressure control valve.

What do you think... should I replace the boost valve?

What about the pressure sensor on the turbocharger... can you buy those individually and replace them?

I am very grateful for your ideas.

Andreas

You could try disconnecting the power to the wastegate control valve. Then, the boost pressure should regulate itself to around 0.6 bar of overpressure.

Regarding VTG vs. Wastegate: A VTG turbocharger has small vanes (guide vanes) that direct the exhaust flow specifically to the turbine. A wastegate turbocharger doesn't have this; it only has a wastegate that opens at a certain pressure, allowing exhaust gases to flow through it. The advantage of a VTG turbocharger is its quick response, even at low RPMs. The advantage of a wastegate turbocharger is its robustness. The wastegate has never failed in any of these, while the VTG has failed more often.

Best regards, WarLord.

So, does the pressure sensor regulate the wastegate... or what?

And is that like a pressure relief valve, and where do the exhaust gases go?

Probably bypassing the charging system and going directly into the exhaust, so it doesn't generate any more pressure... or am I wrong?

BigBabu_ wrote:

So, does the pressure capsule regulate the wastegate... or ?? And is that like a pressure relief valve, and where do the exhaust gases go? Probably past the charging wheel and into the exhaust, so that it doesn't generate any more pressure... or am I wrong about that?

Sure!

Perhaps your wastegate is not closing properly and/or is sticking.

In theory, a severely constricted cross-section of the intake manifold pipe leading to the sensor could also cause a low intake manifold pressure reading. Specifically, the pipe section at the intake manifold runner could be extremely clogged, causing the pressure to build up very slowly behind it.

Disconnect the hose from the pressure sensor, attach a clean hose, and blow into it to see if the air pressure builds up.

Tuppie.

Where is the pressure sensor located exactly? And where is the corresponding hose fitting?

Do you mean the intake manifold? I cleaned that just last week... it was almost clean, and the EGR valve is blocked with a metal plate.

The hose fitting (which is narrowed to just 1mm on the inside) might still be the problem. However, I'm not familiar with your specific vehicle, so you might have to do some searching.

Tuppie.

@ Tuppie and Bigbabu

The AGR model does NOT have the turbo pressure sensor located in the engine control unit (ECU), like the 1Z model does. Instead, it has an external sensor mounted on the intercooler, which is also used to measure the temperature of the intake air.

You can see how a VTG loader adjusts these "little wings" by looking at my avatar.

The turbocharger control valve (N75) likely costs around 30 EUR. It might be a good idea to simply replace it.

Unfortunately, I only know where it's located in the Golf 3 and the Passat 3A.

Here's what it looks like on the Passat:
http://mitglied.lycos.de/matcher76/Bilder/EUV%20vor.jpg


m;

In the A3, it's neatly located next to the AGR valve.
I already bought a new one (size 38 EU). And I will also be replacing the pressure hoses.
I think the pressure sensor is located on the 90-degree bend of the intake manifold, which comes from the intercooler and then goes towards the windshield. But let's see... I'm already close to finding that thing.
I hope it's not because of him, because he already costs almost 100 euros.

Reports will be available... although it might take a little while... because there are so many exams coming up .

Bye Andreas.