Zu wenig Ladedruck <2000U/min, aber keine Ahnung warum | Beiträge 16+

Excuse me, but isn't it logical that low RPMs also result in low pressure and low air mass?

It's a vicious cycle: At low engine speeds, there isn't enough air intake because there isn't enough exhaust pressure to drive the turbo. Consequently, the weakly driven turbo also intakes very little air, which in turn doesn't allow for the full injection amount to be released, because otherwise it wouldn't be possible to burn cleanly (keyword: soot limitation). But even with the reduced injection amount, there isn't enough exhaust pressure to drive the turbo, etc. Eventually, at 2000 UPM, the exhaust pressure is finally sufficient to drive the turbo so that it can build up full boost pressure, the air intake exceeds the target value, and it no longer depends on soot but on torque limitation.

With a diode, the maximum air mass is always reported, and the maximum amount of fuel is injected from idle speed. This causes the turbo to engage earlier because the above-mentioned chain reaction does not occur. As a result, it emits a lot of smoke in the low-speed range because it cannot be burned cleanly, as there is not enough air...

Sven@G4H hat folgendes geschrieben:

When the engine is idling, the EGR valve is fully open, so the engine takes in both uncompressed air and exhaust gases. If the exhaust gases are removed, the engine naturally takes in more uncompressed air. The LMM value increases!

Basically, you're right with the "taking a breath" approach. However, this is because the turbocharger spins faster due to the closed-off AGR (Exhaust Gas Recirculation) system, and therefore draws in more air, and not because the engine is automatically taking in more air. The cylinders are already being filled with excess pressure, so they don't draw anything in.

BeKli hat folgendes geschrieben:

However, to my knowledge, there is no sensor that measures the exhaust gas flow rate.

An indirect measurement exists, via the O2 sensor signal -> Technical article on AGR.

[quote]Excuse me, but isn't it logical that low RPM also means low pressure and low air mass?

It's a vicious cycle: At low engine speeds, there isn't enough air intake, as there isn't enough exhaust pressure at low speeds to drive the turbo.

Basically, yes, but Sven complains that his car has significantly less LD (presumably "Leerlaufdruck" - idle pressure) than other ALH (presumably "Antriebsleistung-Höhe" - power height) vehicles.

@Sven:
There are different MSG (presumably "Motorsteuerung-Grundwerte" - engine control base values) and software versions for the ALH depending on the year of manufacture and the vehicle.

On the ASZ engine in the Golf/Bora and Ibiza 6L, I definitely know that the amount of diesel used in the rev range differs by approximately 10% (depending on the software version).

Result: The Ibiza produces noticeably more torque and power at low speeds compared to the Golf, without any defects.

:idea: Maybe your "problem" is simply due to the software?

Hi,

I'm not just complaining that there's not enough boost pressure on my ALH compared to others, but much more that my ALH doesn't even reach the specified target value at under 2000 RPM, and that's regardless of the software used, because the value is specified and should therefore be achieved. But it's not! I think the problem is that the cycle is like this: too little injection amount --> less exhaust pressure --> the turbo is driven less --> low air mass, and the cycle closes! Now the question is, what's limiting it?

I think the target values for the LMM (lambda sensor) and boost pressure are set by the software (or calculated), so that they should be achieved in operation!

I'm not sure if it's significant, but when the AGR (air-fuel ratio sensor) is open, I don't hear the turbocharger whistling. When I closed the AGR, I suddenly heard the turbocharger whistling noticeably from around 1300 rpm, not whistling but a distinct "peep"! Oh, and yesterday I was at the BA (presumably a testing facility) and it was running at 195 km/h according to the speedometer!

What would you do next? I'm going to try the diode trick tomorrow, but even if that makes it more effective, it's not a long-term solution for me!

Sven@G4H hat folgendes geschrieben:

I think it's likely that the target values for the LMM and boost pressure are set by the software so that they are actually achieved during operation!?

Wrong, at least in the KF (turbocharger) settings, the boost pressure in the low-speed range for high flow requirements usually has values that are not actually achieved in practice.

But that your engine only reaches the target boost pressure at 2000 rpm is probably not the norm.

Zitat:

So würden wir weiter vorgehen?

Den verfügbaren Unterdruck im Pneumatiksystem messen.
Wenn beispielsweise die Pumpe etwas schwach ist, könnte der Druck durch die Vorgabe des LD-TV-KF je nach Menge und Drehzahl auch zu niedrig sein, selbst wenn die VTG im LL bis zum Anschlag gezogen wird.
Ähnliche Auswirkungen könnte ein teilweise defektes Magnetventil haben, oder auch ein Übergangswiderstand in seinem Stromkreis.

Well, in my case, the target boost pressure is also only reached shortly before 2000 UPM. However, this is probably due to the turbocharger and the 2 LLKs.

However, I would also advise you to simply thoroughly depressurize the intake manifold, from the turbocharger to the intake manifold. Defects don't always have to be visible; in my case, one of the LLKs was so leaky that the air escaped just as quickly as I pumped it in with a bicycle pump. However, there was no oil or anything else to be found on the LLK...

If the LLK has a leak, the full boost pressure can arrive a few UPM later, in addition to this, it will also damage the turbocharger in the long run and cause unsightly overboosts.

Hi,
how can I test the suction and pressure hoses, since you mentioned a bicycle pump!?

I just performed the diode test, and the error code showed something about an invalid signal from the LMM (lambda sensor). It didn't go into limp mode, but it ran significantly worse than with the LMM!

How is the vacuum test performed? Can I only test it at idle, or am I mistaken?

-mFg-

Well, the problem reads exactly as I experienced it with my AXR.

You mention that you 'blew through' the vacuum hose, but did you also check for leaks?

'In my case, it was a faulty vacuum canister in the exhaust cooler (which you don't have), which is also operated via the vacuum system. If you have a small leak in the vacuum system, the vacuum pressure may no longer be sufficient to fully close the VTG. This results in a delayed pressure buildup, leading to a lack of bite and slight fluctuations in the boost pressure.

Try disconnecting the vacuum hose directly behind the tandem pump and suck on it. If you can easily remove air, it means there is a leak somewhere.'

I did this with two 50mm drain pipe pieces. I had already measured them. After the turbo, I disconnected one end and inserted a piece (Note: it's best to roughen the end piece and degrease the hose beforehand, otherwise !!!it will blow the part apart!!!). Then, I glued a bicycle valve into the other end (it's best to buy a cheap bicycle inner tube with a Dunlop valve. Cut the valve with a little rubber around it, drill a hole in the end piece, and firmly glue the valve from the inside, e.g. with Pattex extreme. Again, roughen and degrease!)

As a tire pump, I used a standard bicycle pump with a gauge (although it's not very accurate, but at least it's there), and then pumped it up to 1.5 bar. Ideally, the air should not escape anywhere.

As I said, in my case, I didn't even get to 0.3 bar. I pumped air into the tire until I could no longer pull the bicycle pump apart, and the pressure had already escaped from the suction tube...

It might seem complicated now, but it's actually simpler than you think and shouldn't be a problem with a little bit of practical skill

Hi,
Okay, I'll take a look. But I think there might be a small issue here. Why does everything work when idling, even though the vacuum pump should be much weaker since the RPM isn't that high?

Also, could you please tell me how the vacuum is measured (is there a DIY option)? And how are the intake air pipes checked for leaks (is there a trick)?

-mFg-

Sven@G4H hat folgendes geschrieben:

Hi, Okay, ich werde das mal überprüfen. Aber ich denke, es ist ein kleines Phänomen, warum alles ohne Last funktioniert, obwohl die Vakuumpumpe eigentlich viel schwächer sein müsste, da die Drehzahl nicht so hoch ist!?

Ja, aber mit steigender Drehzahl bekommt das Magnetventil weniger Strom, selbst wenn der Soll-LD noch nicht erreicht ist (so funktioniert das LD-Management der TDIs).
Wenn der Unterdruck etwas gering ist, kann das VTG dabei schon vom maximalen Anschlag zurückgehen, während es bei normalem Unterdruck noch am Anschlag bleibt.

Nevertheless, your car should not actually be significantly worse than other similarly sized ALHs (with the same rpm->km/h gear ratios and the same software!) once the power output increases.

Weakness and insufficient boost at low engine speeds point me more towards problems in the fuel system (which also reduces the turbocharger's performance), but this should be particularly noticeable in the Pmax range... quite puzzling :(

[quote]Could you please explain how the vacuum pressure is measured (are there any DIY options)?

1. Using a Saug-LDA (suction LDA)

2. Using a water canister and approximately 25 m of transparent aquarium hose (or similar), including a reserve:
Connect the suction devices to the hose and hang them in the canister.
Hang the middle of the hose approximately 10 meters high, start the motor, and measure how far the water is sucked up from the canister.
Target: approximately 8 meters = 800 mb vacuum pressure.

Make sure that air is never drawn in at the end of the canister, otherwise the water can be sucked up through the highest point of the hose and then probably flow further into the engine:evil:

The same applies if the highest point is lower than the water is sucked up (but not higher than 10 meters = water column for 1 bar).

Otherwise, the method works reliably and is precisely calibrated to 1 cm of vacuum (mbar). After all, you were looking for something for DIY enthusiasts... or would you prefer to buy a vacuum-LDA instead? :twisted:

Zitat:

And how are the air intake pipes checked for leaks (is there a trick)?

See the previous answer!

Hi,
sorry, I hadn't read the previous message yet! I think I'll just buy a suction LDA instead, or try to borrow one somewhere!

I've also been thinking about the fuel supply, but as I said, I've replaced the Dieselfilter and blown the fuel line from the tank to the filter with compressed air. Is there maybe another filter in the tank?

-mFg-

Sven@G4H hat folgendes geschrieben:

I think I'll probably just buy a suction LDA instead, or try to borrow one somewhere!

Too bad, I was secretly hoping for a photo with the pressure gauge :mrgreen:

Zitat:

I've also thought about the fuel supply, but as I said, the Dieselfilter has been replaced and the lines from the tank to the filter have been blown verschandeln with compressed air. Is there maybe another filter in the tank?

Hmm, the parts catalog doesn't show a filter as a separate part. . . . But I can hardly imagine that all the dirt that can get into the tank can also be drawn into the thin lines

Hi,

So, I connected an LDA today. I connected it to the line that goes to the fuel pressure gauge, so that I can directly measure the pressure at the fuel pressure gauge. At idle, it's around 600 mbar, and when I give it full throttle in 4th gear at 1200 rpm, the vacuum drops to 700 mbar and only drops to 400 mbar at 2000 rpm! So, it should be correct!

The behavior is still that it doesn't start pulling/building pressure until around 2000 rpm. What else can I check?

-mFg-

Sven@G4H hat folgendes geschrieben:

The behavior is still that he starts to pull or build up pressure only from 2000 rpm! What else can I check?

For example, a blocked catalytic converter.

Hi,
I've suspected the catalytic converter for some time, but checking it is quite involved, so I want to rule out everything else first! However, this also argues against a clogged catalytic converter, as the speedometer indicates a speed of 195 km/h. Shouldn't a clogged catalytic converter be noticeable at that speed!?

I've just attached the LDA to the air intake. At idle, it shows 0, but the needle only starts to rise when I give it full throttle, and at around 1800 RPM, it shows exactly 1 bar when I'm at full throttle! If I only run it at half throttle and keep it below 2000 RPM, does the needle not move? Does this perhaps indicate a leak in the air intake area, or what do you think? I'm definitely going to buy 2 more gaskets on Monday and check them!

-mFg-