Power loss in the lower RPM range, 1.9 TDI-PD 130 hp

Hello,
I'm new here, and I've already searched the forums, but...
Here's the translation:

"I'm having the following problem with my Golf IV, manufactured in October 2003, with 27,000 km on the odometer, engine code ASZ:"

Leistungsverlust im Bereich 1500 bis 2100 U/min (muß immer öfter am Berg herunterschalten) keine Kraft in diesem Bereich, Schub setzt aber dann ganz plötzlich und abrupt ein(bei ca 2000-2100), weiterhin verzögertes Einsetzen des Antriebsschubes bei vollem Durchtreten des Gaspedals im mittleren Drehz.bereich (2100-3000). In Abhängigkeit von der Belastung(Gang) Setzt der Schub ca 3-5 s (je höher der Gang desto länger die zeit) später ein. MotoHowever, in that mode, it delivers full power and maximum speed.
These symptoms appeared gradually.

During the first inspection at VW, problems were reported. The mass airflow sensor was replaced, but there was no change. The control valve for the turbocharger's vacuum control was replaced, but there was no change. The control valve for the EGR system was also replaced, but there was no change. I had a 100 HP PD Golf as a previous car, which reminded me of the old performance of my Golf. It started pulling strongly from 1500 rpm. Now, VW believes that everything is fine with my Golf and that I am imagining things.

Following that, I conducted measurements of the vacuum pressure at the control unit of the turbocharger during a test run, in order to better quantify my observations. I won't reproduce all the numbers here, but I can say...

The following was observed: At idle (all pressures are negative in bar), the value was approximately 0.5. At 900 RPM, the value was... (The sentence is incomplete).
; 0.4 at 2000; 0.3 at 3400.
In the lower RPM range (1500-2100), with the accelerator fully pressed, the pressure gauge briefly rises from 0.5 to 0.6. At 2000 RPM, the pressure drops abruptly to 0.2, followed by a significant increase in power.
Similarly, when accelerating in the higher gears at a moderate RPM, as soon as the pressure drops after about 3-5 seconds, the power boost kicks in. (Higher gears result in greater lag). The higher the initial RPM, the less the lag.
With small changes in the accelerator pedal, the pressure responds more quickly. During normal driving in higher gears, the pressure is 0.2-0.4 bar. As you approach top speed and under full load, the pressure approaches 0.

My conclusion: The turbo and canister are okay (I checked the hoses and connections for leaks and proper fit, and there's no sign of damage from rodents).
AGR cannot be the cause, otherwise you would experience power loss and soot formation even at higher engine speeds.
Only the turbocharger control system, or some other sensor, or the interaction between the EGR system and the vacuum control system, remains to be investigated. What is causing the delay? (Is it an overreaction, or a short-term limp mode, triggered by too rapid an increase in boost pressure?)

I'm curious to know if anyone else is experiencing similar problems. I will definitely continue to deal with VW regarding the warranty and won't just accept it, as it was expensive enough.
Best regards, Cetano.

Hi,

Are you sure that the vacuum cylinder is actually moving the VTG (valve)? To me, it sounds like the VTG is sticking, and only moves when there is sufficient vacuum pressure.

Test: Connect a vacuum hose from the VTG sensor to a LARGE syringe, then pull on it with force. This should allow the VTG to move smoothly and without jerking from stop to stop.

She doesn't do it: Apply copper paste (and hope that the VTG doesn't get stuck in turbo) and then either manually adjust the mixture with the syringe, or try Ulf's trick (-> search).

Best regards,

Jan.

In my opinion, a sticking VTG (vacuum transducer gauge) is not the cause, because if that were the case, the vacuum would increase, and the thrust would start delayed in relation to the pressure drop (the sensor would react late). However, the pressure drop and the thrust occur simultaneously.

To me, that sounds quite logical. The moment the turbocharger builds up the desired pressure, the control unit is satisfied and stops working so intensely on the VTG (Variable Turbine Geometry), effectively reducing the vacuum to prevent a sudden and violent overboost.

cetano wrote:

I don't think a sticking VTG is the cause

, because if that were the case, the vacuum would increase, and the thrust would start delayed in relation to the pressure drop (the canister would react late). However, the pressure drop and the thrust occur simultaneously}.
It might be... but for a more detailed analysis, we would need the logs from the turbocharger pressure control system and the throttle position sensor, recorded during the time the error occurs.

Hi,

Cetano, I don't have an answer to your silly problem, but I'm experiencing the exact same issue with my Seat Leon 1.9 TDI with 130 horsepower.

I bought it brand new in April 2004, and the problem you described was present from the very beginning. I initially attributed it to the break-in period, and it did improve somewhat over time, but I've now driven 10,500 km. This delayed power delivery occurs mainly in my Leon when the weather is very hot.
I had everything checked by a Seatmann technician, and he couldn't find anything wrong. The temperature sensor readings are normal, the pressure sensor has also been checked, and all other values were apparently also okay.

However, on some days it runs perfectly normally, pulls strongly from low RPM, and revs up smoothly. I've also considered a sticking VTG (variable turbine geometry), but I haven't checked it yet, as the problem isn't currently occurring.

Perhaps someone in this forum can provide an answer; I would be very interested to hear it!

Regards,

amd-ede

Following your good advice, I re-examined the VTG (Variable Turbine Geometry) control unit on the turbocharger. Using a vacuum pump and a vacuum gauge, I tested it. It functions perfectly (without any sticking) and operates linearly across a pressure range of 0 to -0.6 bar (at each end of the control lever's travel), so the problem is not likely to be with the control unit itself.
"With the help of VAG software, I believe it's possible to record data from multiple channels (e.g., accelerator pedal potentiometer, boost pressure, VTG vacuum, engine speed) simultaneously, especially during critical situations (which is what I've done using rudimentary methods)."
It's probably difficult, and not every expert is motivated to find mistakes...
On Friday, I have an appointment with the relevant engineer from VW (at my request). I will provide further updates.

Here's the translation:

"New update: A VW service engineer from Wolfsburg was here. He talked about things like power output and tolerances, etc. (He was a bit unapproachable, wearing a tie and collar). He didn't provide any information to the customer. I returned the car yesterday (for the 4th time). They want to run a few more tests (deactivating the AGR system temporarily, replacing various vacuum-controlled valves again, and...). "
The EGR valve appears to be heavily carbonized (which is not surprising, given a return rate of up to 40%).
VW has everything under control... it's so exciting... keep us updated.

@cetano:

Are you aware that the 74 kW motor generally responds better at lower speeds compared to the ASZ?
I've already driven a Golf IV with the 74 kW engine twice, and it performs "in the lower RPM range" better than all the ASZ engines I've driven so far.

It is also somewhat normal for the tearing process to begin quite abruptly at an ASZ (Air Separation Zone) speed of around 1,900-2,000 revolutions per minute.
Do you perhaps have the opportunity to visit another service center for comparison? Hmm, a turbo lag of 3-5 seconds is definitely too much.

Given the EGR issue, I'm a bit surprised, especially considering the mileage. My intake manifold looked almost new at 30,000 km, with a thin layer of soot in some places, but also some areas that were still metallic and shiny. I drive a lot on the highway. Do you perhaps drive mostly in the city? If so, have the dealer thoroughly verschandeln the intake manifold under warranty and then permanently disable the EGR system.
Since you mentioned carbon buildup, I would suspect the EGR valve. It can significantly affect the engine's response if it closes slowly. However, if that's the case, you should also be able to see soot.

Roger wrote:

Are you aware that the 74 kW engine, from the start, generally responds better in the lower RPM range compared to the ASZ? . . .Hmm, 3-5s Turboloch sind jedenfalls eindeutig zuviel.

. . . when at least ~1700 rpm is applied.

Therefore, I also believe that something is wrong with cetano and amd-ede's car.

If both had an LDA, a direction for further investigation could already be derived from that .

Quote:

. . . wenn mindestens ~ 1700 rpm anliegen.

He wrote about the range between 2,100 and 3,000 RPM. At 1,700 RPM, I would still describe it as a lack of initial acceleration, but when I press the accelerator at 2,100 RPM and have to wait, I would call it turbo lag.

Thank you for your message. Regarding the AGR valve, I hope that VW will verschandeln the intake manifold as well. They will probably replace the entire valve. I haven't noticed any unusual noises. I mostly drive long distances and use the pre-heating function (standby heater).
The 100 hp PD engine really delivers good power from low RPMs, but it didn't perform like this before.
"Perhaps it's a small issue with a significant impact (e.g., the turbocharger boost pressure overshoots, and the control unit reduces the boost pressure using the variable geometry turbocharger until a constant boost pressure is achieved, or the control unit may need a reset, possibly by reflashing the software or replacing the control unit, or something else...). I also have the diesel fuel return temperature sensor and the intake air temperature sensor at the intercooler on my list of possible causes."There's still a warranty on it, so before I come up with any solutions, I'll have it checked and repaired by VW first.
"And for as long as it takes, I'm driving a rental car that costs me nothing. Right now, it's a brand new Caddy with a payload capacity of 750 kg and a 51 diesel kW engine. This is the last car I'll be driving for a while... I'm already missing my T3 Doka (of course, a diesel, a reliable one)."

Hi cetano,

das könnte eine falsche VTG-Stellung am Anschlag im geschlossenen Zustand sein (max. Unterdruck in der Steuerdose). Ich meine damit, das die geschlossenen Schaufeln der VTG den Turbinenzustrom schon soweit verschließen, den Abgasstrom drosseln und sich so kein Ladedruck mehr aufbauen kann (Wirkt wie eine Motorbremse). Es gibt hier eine Einstellschraube mit Kontermutter für diesen Anschlag. EA single rotation is enough to slightly open the blades again, bringing them back to their full range of motion.
Therefore, your measurements make sense. The jump from 0.6 to 0.2 bar of control vacuum causes the boost pressure to build up only when the variable turbine geometry (VTG) opens.

Best regards from Sepp.

Sepp wrote:

This could be due to a misaligned VTG position at the stop in the closed state... There is an adjustment screw with a lock nut for this stop. Just a single turn is enough to open the blades slightly at the stop. Therefore, your measurements make sense. The jump from 0.6 to 0.2 bar of control vacuum below atmospheric pressure is only achieved by opening the VTG, which then builds up the boost pressure.

Hello Sepp,

An interesting theory.

While this would be the first case of its kind that I've heard of, it seems generally plausible to me.

If VAG (Volkswagen Audi Group) doesn't have any other solutions besides replacing the charger, and that fixes the problem, then that would support your assumption... let's wait and see.

He's driving again, just like the old days.

After 2 days of intense work at VW, it's finally done. My doubts disappeared after the test drive with the service technician, who had the best understanding of the issue and who worked closely with Wolfsburg on this problem (via hotline, multiple times).

Regarding Sepp's suggestion: How can the alignment shift, especially after 30,000 km? Or could there be a material-related change (slight deformation due to heat)?
I also asked the service technician. It could be a possibility, but determining the extent to which changes would be necessary would require further testing and time.

In summary: VW performed the diagnostic test using VAS 5051 (on a stationary vehicle) for the tenth time. All modules were checked, including functional tests.
"So-called fault-triggered tests were performed. For example, when the possibility of temporarily disconnecting the intake air temperature sensor is selected, the program instructs the user to remove the sensor and spray it with refrigerant while it is connected. Only when the temperature reading drops is it confirmed that the sensor is functioning correctly."

During this diagnostic procedure, which was guided by error codes, the boost pressure was also checked while the engine was idling at 1400 rpm and at operating temperature. (The engine speed is maintained by the engine control unit).
Here's where the error occurred:

"Report: The boost pressure control is not working correctly. The values are:
Air pressure: 995 mbar. Duty cycle: 0 percent.
Air pressure: 948 mbar. Duty cycle: 99 percent.
The difference in air pressure is 48 mbar, which is outside the expected range of 100 to 200 mbar.
- Check the valve as follows:
Is that clicking sound audible?
Is the linkage not moving because the magnetic valve is not working?
Moved ...........................not, although the M........ is working?" (the corresponding key must always be pressed)

"... Since the connecting rod is functioning correctly, but the boost pressure was not achieved, the problem must be with the turbocharger - Replace the turbocharger..." (I obtained the log on land)

And that's exactly what VW did, after the service technician called Wolfsburg again. There, they doubted the test and assumed that the technician had accidentally pressed the wrong button. However, the repeated test confirmed the situation.
There was nothing obviously wrong with the old loader, but it's a world of difference, like night and day. I just don't understand it...

I also have the vacuum circuit diagrams for ARL, ASZ, and AXR engines (for anyone who needs them...).
I'm sorry it's so much, but I think it's all important.
Thank you again for your ideas.

"How is it possible that the boost pressure control isn't working within the specified range, but then the turbocharger is simply replaced?"
Please correct me if I'm wrong, but to me, this suggests a potentially faulty VTG (Variable Turbine Geometry) canister or a malfunctioning boost pressure control valve, but not necessarily a faulty turbocharger itself. Furthermore, the linkage seems to be functioning.

What do the others think?