Insufficient charging pressure <2000U/min, but I don't know why.

Hello,

This is regarding a Golf 4 with the ALH engine and a faulty AGR valve. Three weeks ago, a new turbocharger was installed under warranty because the old one's VTG linkage was constantly breaking. The car already lacked power and torque below 2000 rpm with the old turbocharger, and it's the same with the new one! The latest logs (unfortunately, I can't upload them here because I don't know how) show that the boost pressure (at full throttle in 4th gear) is approximately 400 mbar below the target value at 1200 rpm, 200 mbar at 1600 rpm, and around 80 mbar at 2000 rpm, which lasts until 2300 rpm, after which the boost pressure is almost exactly at the target value! The pedal travel is 24.7% below 2000 rpm, which is actually too high! Or?

The air mass is 1200U/min, 300mg/H below the target value, and crosses the target line at 1600U/min, exceeding the target value by 200mg/H! The maximum value of the LMM is 1050mg/H! The minimum limit is always the torque limit starting at 1100U/min.

I have already read numerous technical articles, including those related to troubleshooting, but I'm still not making any progress! I have already done the following:

- Bleed the vacuum system
- Replaced the fuel filter and blew out the lines with compressed air
- Tested and inspected the injectors, OK
- Cleaned and inspected the air-water cooler and pressure lines for leaks
- Checked and cleaned the intake system for leaks
- Tapped the exhaust system with a hammer – no knocking sounds

I really don't know what to do anymore, oh yeah, and the error memory is also empty! What do you think I should do next???

-mFg-

Hey.
How was was the AGR shut down? Was was it, foreign objects in the pipe...?
<TAG2>What does 'The VTG linkage was regularly checked' mean? You can usually tell if the VTG linkage is worn by around 2000 rpm.
Do you have an LDA on board? Have you checked the air filter already?! Have you also logged group 3 and 8?

Hi,
AGR was shut down using sheet metal and the second seal, as well as a foreign object in the vacuum line! The one with the wobbly VTG was shut down with the old turbocharger, of course, you would have noticed that above 200 U/min, but the current VTG is functioning 100%! I don't have LDA on board! The intake path was completely checked and cleaned, all the way to the headlight! I also logged groups 3 and 8. MWB 3 was described above with the air mass values, and MWB 8 should be okay since the torque limit is lowest at 1100 U/min!

I also forgot to mention that I meticulously checked the timing (using a camshaft ruler), as well as the injection start time. The injection start time is exactly between the target value and slightly ahead, so it's actually perfect!

Ultimately, I think the problem is simply that the throttle ratio of the fuel injection control valve at full throttle at low engine speeds is only 24.7%, but it should actually be close to 0% since the VTG must be set to maximum fuel injection pressure! The question is just why the TV doesn't go any lower?

-mFg-

hi

Let's try a 3, 8, 11 log with full load acceleration of 1000-4000 U/min, then we should be able to get some useful data...

m;

Zitat:

The minimum limit is always the torque limit!

Well, that's fine.

Because that's normal, the torque limit is always the lowest during acceleration.

You can also find the log somewhere on the internet and enter the URL here.
There's free web space everywhere.
m;

Sven@G4H hat folgendes geschrieben:

Ultimately, I think the problem is simply that the throttle ratio of the fuel injection control valve at full throttle at low speeds is only 24.7%, and it should actually be close to 0% since the VTG must be set to maximum fuel injection pressure! The question is just why the TV doesn't go any lower!?

Because that's what it says in the software: wink:

To reassure you, try the following:

Feel your way around the cold, stationary engine to the VTG (Valve Timing Gear) bar and note where you need to apply pressure.

Then start the engine, quickly reach for the VTG bar again (before it gets too hot) and try to push it towards the can.

If it doesn't move at all, it's already at its limit, as approximately 600 mb of vacuum are required here, but the pump normally delivers around 800 mb.

Hi,
The VTG bar is definitely at its limit when the engine is idling!
Here are the logs, I hope they work!

http://www.geocities.com/sveng4h/Begrenzungen.JPG

http://www.geocities.com/sveng4h/Ladedruck.JPG

http://www.geocities.com/sveng4h/Luftmasse.JPG

-mFg-

I think the whole issue is a problem of engine management with the turbocharger boost control due to the lack of exhaust gas recirculation (but I'm happy to be corrected).

The engine control unit naturally relies entirely on the mechanical characteristics of the engine. If you simply disable the AGR without the engine control unit adapting to the new conditions, it is clear that the engine will not run as it should in many areas (Incidentally: do you think the AGR was invented so that you could disable it and thus lose your TÜV, MOT, insurance coverage and warranty?).

However, if you're still thinking about your case, it's strange that the boost pressure is below the target value (when the AGR is disabled, it should always be above). There's probably only a leak or a faulty pressure sensor or valve. Are you sure you didn't mix up the target and actual boost pressure values? That would certainly make sense. The fact that it lacks "bite" could also be due to incorrect air-fuel mixture formation due to the lack of AGR.

If the mass airflow sensor response was logged during startup, I would say that indicates a leak in the line to the MAF sensor. How did you check for leaks in the intake system?

Edit: Also, laut deiner Liste hast du auch noch nicht überprüft, ob dein stillgelegter AGR-Ventil dicht ist. Wenn das natürlich undicht ist (was natürlich von der Motor-/Abgastemperatur abhängen kann, wer weiß was du da gebaut hast ), dann hast du einen Fehler.

...and if the LMM is simply not responding?

If you already have the AGR, you can try the diode trick.

My old 1Z is now running much better at low speeds with a diode, because it doesn't need to regulate the pressure itself to bring the turbo to boost.

You have also not yet checked whether your deactivated AGR is sealed.



I would also check that. I once had a case where a friend's sheet metal had rusted through (he had used 0.4 mm steel sheet, well, it lasted about half a year... ).

[quote="ampac"]This can also be due to incorrect mixture formation due to a malfunctioning AGR.

BeKli hat folgendes geschrieben:

You haven't really grasped the principle/function of the AGR in diesel engines, have you?!

The AGR reduces the air mass in the cylinder; if it's missing, the air mass would have to be too high in certain operating conditions, resulting in a lean mixture. That was my thought process.

@ BeKli

Zitat:

The AGR reduces the air mass in the cylinder

Not quite correct.
The air mass – or what is generally referred to as such – is the "fresh air mass".

The rest is drawn out of the exhaust, which consists not only of mass-less, non-usable components for combustion.

When it comes to diesel engines, the terms "mixture formation" and "lean/rich" are rarely used.

A diesel engine always runs "lean", meaning with an excess of air – our TDI even with a 20% excess.

Zitat:

The engine control system naturally relies completely on the mechanical properties of the engine.

That's also not entirely correct. This is the key difference between control and regulation.

A control system simply says "do it like this" and assumes it's sufficient.

A regulation system measures and corrects.

The AGR (Exhaust Gas Recirculation) is regulated - however, relatively independently of the other engine parameters, so deactivating it has no (performance-wise, rather partial) effect.

Hi,
The AGr is 100% airtight. I have a sealing material, stainless steel sheet, and another sealing material, and I tightened the screws again after 100km! I only visually inspected the intake pipe.

The LMM value is naturally too high at idle, as this is where the exhaust gases from the AGR are missing, and therefore the required air passes completely through the LMM. This should also be the case at full throttle, as the AGR should also be open there! You can also see in the diagram that the air mass is much too high from 200 U/min, normally it is around 850, but it is 1050, but this should not be a problem as the boost pressure is correct at speeds above 2000 U/min!

Why is the LMM value so low at low RPM? Could a faulty LMM be providing incorrect readings at low RPM, while functioning correctly at high RPM?

-mFg-

Sven@G4H hat folgendes geschrieben:

Hi, The LMM value is naturally too high at idle, as there is no exhaust gas from the AGR to compensate, and therefore all the required air passes through the LMM.

I don't quite understand what you mean, but in any case, only the unmetered fresh air passes through the LMM.

dieselmartin hat folgendes geschrieben:

The AGR is controlled - however, it is relatively independent of other engine parameters, so deactivating it has no effect (in terms of performance, rather partial).

I understand the difference between control and regulation; no problem.

However, to my knowledge, there are no sensors that measure the amount of exhaust gas returned. Therefore, the ECU must rely on the AGR valve adjustment, which it probably does. However, if the AGR valve is closed, the ECU can adjust it as it pleases, as the amount of exhaust gas returned is naturally always 0. But the ECU doesn't notice this.

Or am I wrong again?

Sven@G4H wrote:
Hi,
The LMM value is naturally too high at idle, as there is no exhaust gas from the AGR in this case, and therefore the required air passes completely through the LMM.

BeKli wrote:
I don't quite understand what you mean. However, the uncompressed fresh air always passes through the LMM.

When the AGR is fully open, the engine takes in both uncompressed air and exhaust gases. If the exhaust gases are no longer present, the engine naturally takes in more uncompressed air. This causes the LMM value to increase!
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