Low Boost Below 2000 RPM - Troubleshooting Guide

Hello,
es geht um einen Golf 4 mit dem ALH Motor und defekter AGR, vor 3 Wochen wurde auf Garantie ein neuer Turbolader eingebaut weil beim alten das VTG Gestänge regelmäßig gehangen hat, dem Auto fehlte mit dem alten Lader unter 2000U/min schon der Biss bzw. spürbar Leistung und mit dem neuen Lader ist es genauso wie vorher! Die letzten Logs (kann sie leider nicht hier reinstellen da ich nicht weiss wie) zeigten das der Ladedruck (bei Vollgas im 4. Gang) bei 1200U/min ca. 400mbar unter dem Sollwert liegt, bei 1600U/min noch 200mbar unter dem Sollwert, bei 2000U/min fängt dann ein Überschwinger (Istwert geht über Sollwert) von ca.80mbar an der bis 2300U/min andauert, danach liegt der Ladedruck ziemlich genau auf dem Sollwert! Das Tastverhältniss ist unter 2000U/min bei 24,7%,also eigentlich zu hoch! Oder?

The air mass flow rate is 300 mg/h below the target value at 1200 RPM, but crosses (actual value exceeds target value) the target line at 1600 RPM and then goes 200 mg/h above the target value! The maximum value of the air mass flow rate is 1050 mg/h! Below 1100 RPM, the torque limit is always the limiting factor.

I've already read all the relevant articles and search results on this topic, but I can't figure out what's causing the error! Here are some things I've already tried:
- Vacuum hose blown.
- Replaced the fuel filter and blew out the lines with compressed air.
- Have the fuel injectors checked for leaks and have their spray pattern inspected; OK.
- Intercooler and pressure pipes cleaned and checked for leaks.
- Intake path checked for leaks and cleaned.
- Tapped the exhaust with a hammer --> no rattling noises.

I'm really at a loss now and don't know what else to do. Oh yeah, and the error memory is also clear! What do you think I should do next?

-Sincerely-,

Hello.

How was the EGR valve disabled? Was it due to metal debris, foreign objects in the hose, ...?

'What does it mean that the VTG strut was regularly engaged? You can usually tell when a VTG is malfunctioning, even above 2000 rpm.'
Do you have a landing gear indicator (LDA) on board? Have you checked the air filter yet?! Did you also log data for groups 3 and 8?

Hi,
AGR was shut down due to a leak with the metal plate and secondary seal, as well as a foreign object in the vacuum hose. The issue with the variable turbo geometry (VTG) you mentioned existed with the old turbocharger. Of course, it was noticeable even outside of the 200 RPM range back then, but the current VTG is working perfectly! I don't have any LDA (Lambda Probe) installed. The intake path has been completely checked and cleaned, all the way up to the headlight. I also logged data from groups 3 and 8. As mentioned above, MWB 3 (Mass Air Flow) shows the air mass values, and MWB 8 should be fine because the torque limitation is lowest at 1100 RPM.

I forgot to mention that I also checked the valve timing (carefully verified with a camshaft alignment tool) and the injection timing. The injection timing is exactly between the target value and slightly advanced, which is actually perfect!

Ultimately, I think the problem is simply that the boost control valve's throttle ratio only reaches 24.7% at full throttle in lower RPM ranges, and it should ideally be close to 0%, as the variable turbine geometry (VTG) needs to be set for maximum boost! The question is, why doesn't the TV go any lower?

-Sincerely-,

hi

"Try setting the logging to channels 3, 8, and 11 while running at full load with acceleration between 1000 and 4000 RPM; you should be able to get more useful readings that way."

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Quote:

Below 1100 RPM, the torque limit is always the limiting factor.

"Well, that's okay."

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

You can disable the logging somewhere on the internet and then just paste the URL here.
Free web space is available everywhere.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Sven@G4H wrote:

Ultimately, I think the problem is simply that the throttle valve ratio of the charge pressure control valve only reaches 24.7% at full throttle in lower RPMs, and it should actually be close to 0%, since the variable turbine geometry (VTG) needs to be set for maximum boost pressure! The question is, why doesn't the TV go any lower!?

Because that's what it says in the software .

To help you calm down about this, try the following:

Feel your way along the VTG rod (with the engine off and cold) to find where you need to grip it.
Then start the engine, quickly grab the VTG rod again (before the area gets too hot), and try to push it towards the can.

If it doesn't move even a millimeter, then it's also at its maximum capacity with 24%, because approximately 600 mbar of vacuum pressure is required for that, but the pump normally delivers around 800 mbar.

Hi,
"You're right, the VTG rod is definitely hitting the limit in idle mode, touching the load cell!"
Here are the logs; I hope it works!

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

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

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


-Sincerely-,

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

The engine control unit (ECU) relies entirely on the mechanical conditions of the engine. If you simply disable the EGR system without informing the ECU about the new operating conditions...
It is clear that the engine no longer operates as it should in many areas (By the way: do you think the EGR was invented so that you would disable it, thus losing TÜV [German technical inspection], AU [exhaust emissions test], insurance coverage, and warranty?).

However, despite everything, it's strange that the boost pressure is below the target value (when the EGR system is deactivated, it should always be above). It could only be a leak, a faulty pressure sensor, or a defective valve. Are you sure you haven't mixed up the target and actual boost pressure values? That would actually explain it. The lack of power could also be due to incorrect air-fuel mixture caused by the missing EGR system.
If the air mass flow sensor data was logged during startup, I would say that it looks like there's a leak in the intake manifold leading to the MAF sensor. How did you check the intake path for leaks?

Edit: According to your list, there's also something else you haven't checked yet: whether your deactivated EGR valve is sealed. If that's leaking (which could depend on the engine/exhaust temperature, who knows what you've done ), then you've found your problem.

...and what if the mass airflow sensor is simply broken?

If you already have the AGR (automatic air recirculation) system enabled, you could try the diode trick.

My old 1Z engine performs much better at low RPMs with the diode modification because it doesn't restrict the pressure it needs to spool up the turbocharger.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

The lack of bite could also be due to incorrect fuel mixture caused by the absence of an EGR system.

You really haven't understood the principle or function of the diesel exhaust gas recirculation (EGR) system, have you?

According to your list, there's also something else you haven't checked yet: whether your deactivated EGR valve is sealed properly.

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

ampac wrote:

BeKli wrote: The fact that it has insufficient bite could also be due to incorrect fuel mixture resulting from a missing EGR system. You really haven't understood the principle or function of the diesel EGR system, have you?

The AGR (Abgasrückführung) reduces the amount of air entering the cylinder. If it were absent, the air mass would be too high under certain operating conditions, ultimately leading to a lean fuel-air mixture. That was my reasoning behind it.

@ BeKli

Quote:

The EGR valve reduces the amount of air entering the cylinder.

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

The remaining components are extracted from the exhaust gases, which not only consist of substances that are useless for combustion but also contain other elements.

When talking about diesel engines, the terms "mixture formation" and "lean/rich" are not typically used.

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

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Quote:

The motor control system naturally relies completely on the mechanical aspects of the motor.

That's not entirely correct either. That's the crucial difference between control and regulation.

The new control system simply says "do it this way" and assumes that it will work.

A regulation measures and corrects.

The AGR (Abgasrückführung) system is controlled, but it operates relatively independently of other engine parameters. Therefore, disabling it has little effect on performance; it might slightly alter the exhaust gas composition instead.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi,
"The AGr (presumably a component) is completely sealed; I have a gasket, then a stainless steel plate, another gasket, and the screws were tightened again after 100 km! I only visually inspected the intake manifold!"

The mass airflow sensor (MAF) value is naturally too high at idle because the exhaust gases from the EGR system are missing, meaning all the required air passes through the MAF. It should theoretically be the same at full throttle since the EGR would also be open then. As you can see in the diagram, the airflow mass is much too high starting at 200 RPM; normally it's around 850, but it's showing 1050. However, that shouldn't be the problem because the boost pressure seems correct at engine speeds above 2000 RPM.

Why is the mass airflow sensor (MAF) value so low at low engine speeds? Could it be that a faulty MAF sensor provides incorrect values at low speeds, but functions correctly at high speeds?

-Sincerely-,

Sven@G4H wrote:

Hi, The mass airflow sensor (MAF) reading is naturally too high at idle because the exhaust gases from the EGR system are not present, meaning that all of the required air passes completely through the MAF.

I don't quite understand what you mean, but in any case, the LMM (likely referring to a Low Moisture Membrane) only allows fresh air that hasn't been compressed to pass through.

dieselmartin wrote:

The AGR valve is controlled, but it operates relatively independently of other engine parameters, so deactivating it doesn't really have a significant impact on performance; it might slightly affect emissions instead.

I know the difference between control and regulation, no problem .
To my knowledge, there is no sensor that measures the amount of exhaust gas being recirculated. Therefore, the ECU must rely on the EGR valve setting, which it probably does. However, if the EGR system is disabled, the ECU can adjust the valve as it sees fit, but the actual amount of recirculated exhaust gas will always be zero, although the ECU doesn't detect this.

Or am I wrong again?

Sven@G4H wrote the following:
Hi,
The mass airflow sensor (MAF) reading is naturally too high when idling because the exhaust gases from the EGR system are not present, meaning that all of the air being drawn in passes completely through the MAF.


BeKli wrote the following:
I don't quite understand what you mean, but in any case, the LMM (likely referring to a Low Moisture Membrane) only allows fresh air that hasn't been compressed to pass through.



When the engine is idling, the EGR valve is fully open, allowing it to draw in uncompressed air and exhaust gases. If the exhaust gases are reduced, the engine naturally draws in more uncompressed air, which increases the mass airflow sensor (MAF) reading.
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