VW Golf 4: Turbocharger Issues & High Fuel Consumption

Hello everyone,

I've been passively following for a long time, but I've now registered because I'm stuck on a current problem and can't seem to find a solution. First, let me introduce myself. I'm 31 years old and drive a Volkswagen Golf 4 Variant 1.9 TDI AXR, manufactured in 2002, with 220,000 km on the odometer. It's mainly used for long-distance driving (about 230 km twice a week, very little city driving). I meticulously maintain the car, and it has never let me down before.
Angefangen hat mein Problem, dass ich von heute auf morgen einen sehr hohen Momentanverbrauch (ich weiß - Momentanverbrauch laut Anzeige ist nicht wirklich aussagekräftig) bei moderatem Beschleunigen im 1. und 2. Gang von teilweise über 40l/100km festgestellt habe. Früher ging dieser Wert nie bis 20l/100km. Daraufhin habe ich mich auch durch diverse Themen hier im Forum genau mit dem Thema beschäftigt und etliche Sachen untersucht. Der Durchschnittsverbrauch über inzwischen mehrere Tausend km ist seit dem auch um über 1l/100km gestiegen. Außerdem habe ich vor allem durch Logfahrten mit VCDS-Lite herausgefunden, dass der Ist-Ladedruck deutlich über Soll ansteigt, dann wieder deutlich unter soll abfällt und schließlich mit mehreren Überschwingern sein finales Soll von 2040mbar erreicht. Nach dem ersten Abfallen des Ladedrucks ist im MWB3 kurzzeitig die Rußbegrenzung der niedrigste Wert. Auch die VTG-Ansteuerung in MWB11 fällt zum selben Zeitpunkt ab. Ich kann jedoch nicht sagen, was Ursache und was Wirkung ist. Im Fehlerspeicher ist nichts hinterlegt und auch in den Notlauf ist der Motor noch nie gegangen. Insgesamt läuft der Motor sehr ruhig und gleichmäßig. Startprobleme auch bei den jetzt sehr kalten Temperaturen gibt es nicht. DiI recently reached a top speed of just under 200 km/h.

Here's what I have done so far:
- Error memory: empty.
- Brakes inspected --> uniform heating on both sides, within a range of +/- 2°C.
- Temperature sensors in a cold engine (MWB 7): Intake manifold and coolant temperatures are the same, fuel temperature is 1.2°C lower.
- When the engine is not running: Intake manifold pressure and atmospheric pressure are identical.
- Air filter: new.
- Fuel filter: new.
- LMM: new.
- EGR valve: new.
- Vacuum hoses were individually inspected for damage and, if there was any doubt, replaced as a precaution.
- The EGR valve and the turbocharger solenoid valve were swapped.
- Exhaust manifold to EGR cooler connecting pipe: replaced due to a leak.
- Charge Air Cooler (CAC) with control valve: new, but the lever on the vacuum actuator is broken.
- The VTG (Variable Turbine Geometry) linkage retracts smoothly by approximately 1 cm when the engine is started. Additionally, I have manually moved it back and forth about 500 times using a syringe - it moves smoothly to both end positions, whether the engine is cold or warm.
- Seals for the charge air system: new.
- The intake air path from the air filter to the EGR valve was depressurized as much as possible using a bicycle pump compressor. Approximately 30 seconds after stopping the pumping process, there was still pressure in the system when the valve was opened.
- I tapped the exhaust system with a rubber hammer: no rattling was detected. I also believe that if the catalytic converter is clogged, the overall boost pressure would be too low. However, in my case, it fluctuates around the target value at low RPMs.

Attached you will find a processed log file (created with VCDS-Lite) of measurement blocks 3, 8, and 11 from a full-load acceleration in 5th gear. For testing purposes, I temporarily disabled the EGR valve by blocking the vacuum hose. However, this did not result in any change compared to having the EGR valve activated. Worksheet 2 contains another log recording using only measurement block 11, to obtain a finer time resolution (I'm not sure if this alone will help).

So, you can see that I've already done a lot on my own, and now I'm eager to hear your ideas. I'm really at the end of my rope and hope that you can help me.

Sure, here's the translation:

"Thank you in advance!"

Regards,
Steffen.

Hmm, the MWB11 log data seems to indicate a mechanical jam (e.g., VTG or N75 valve) or excessive play in the mechanical control system.
You've practically ruled out any issues related to the ease of movement test or the EPW replacement.

So, it seems the only option left for me is to get an explanation of how the game works. With over 200,000 km on the odometer, the problem could very well be in the VTG (Variable Turbine Geometry) mechanism, meaning that without a new or refurbished turbocharger, you probably won't get rid of the issue.

ulf wrote:

So, it seems the only option left for me is to explain the game.

I'm not a Loader expert, but besides the game explanation, could an overly aggressive control signal (i.e., a misaligned VTG rod) also be an explanation?
However, I also don't understand how they could possibly get misaligned from one day to the next.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It can also be used as a verb, meaning "to gust."

guste100 wrote:

but besides the explanation of the game malfunction, wouldn't an overly aggressive control (i.e., a misaligned VTG rod) also be an explanation?

Yes: for the initially too high charging pressure.
More likely no: this is due to the constant oscillation between the actual value and the setpoint. In a properly functioning control loop, this oscillation should stop after a maximum of two cycles, even if the offset is not correct (which could indicate a misaligned potentiometer linkage).

Hello everyone,

First of all, thank you for the initial responses.
Since I can't detect any jolts or jamming in the VTG adjustment, I would actually like to rule out this issue.

I may have forgotten an important detail when describing the problem. Specifically, the instantaneous fuel consumption reading on the display jumps sharply upwards as soon as I slightly press or release the accelerator pedal. It's between 5-10 liters per 100km in lower gears, but significantly less in higher gears.

I'm not sure if a certain noise is related to the intercooler issue or something else entirely. Especially when accelerating with a cold engine, there's a whistling sound coming from the front right area (which could be escaping air) when I release the accelerator for gear changes. This is particularly noticeable when accelerating close to walls. However, this has been happening since I bought the car over 70,000 km ago, and until recently, it hasn't affected fuel consumption. I can't definitively say whether it has gotten worse or not. What speaks against it being related to the intercooler problem is that I thoroughly checked the entire intercooler system for leaks and found nothing. If there's a small hole somewhere in the system (e.g., caused by rodents), could this explain the measured curves?

Could you perhaps tell me again if I'm doing something wrong when creating the vacuum? I bought a vacuum kit and connected the air inlet side to the hose from the air filter. I connected the sealing plug with the hose in front of the EGR valve. Since there is a quick-release coupling here instead of a hose clamp, and the plug doesn't seal completely as a result, I wrapped some sealant tape around it. However, I have now ordered a suitable hose to ensure that it is 100% airtight. After that, I pressurized the system to about 1 bar using a bicycle pump and didn't notice any whistling sounds.

Regards,
Steffen.

The AXR is a pump-injector (PD) engine, where the fuel injection quantity is calculated based on the opening times of the PD injectors. If you experience unusual behavior in the fuel consumption display, such as fluctuations when releasing the accelerator pedal, I would also investigate potential electrical problems, such as sensors for throttle position or ground connections.
Do the fuel injection amounts logged via VCDS and the throttle position sensor value exhibit similar behavior to the fuel consumption display?
hg
Herbert.

Hello Herbert,

Okay, that's not good news... electrical connection problems don't sound promising at all. I honestly have no idea where to even start looking.

Which specific values for fuel injection quantity and throttle position sensor readings are you referring to? What kind of test drive should I perform here, including a full-throttle acceleration test? Which diagnostic trouble codes (DTCs) should I log?
I only checked the values from 0-100% of the accelerator pedal position (the last value in the diagnostic data block 10) while the engine was idling. It felt like these values accurately reflected the actual accelerator pedal position.

What additional measurements can I take to narrow down the source of the error? Where and how would you look for contact or ground faults?

Regards,
Steffen.

Hi Steffen,
Unfortunately, I can't tell you exactly which specific data points those are, but you can find them yourself. In any case, you will need the throttle position and the fuel injection amount. If the fuel consumption is also available through these data points, that would be even better. And of course, including the engine speed would make sense.
And then you need to reproduce the high power consumption reading and the behavior when gas is depleted during the logging process.
hg
Herbert.

Herbert wrote:

Unfortunately, I cannot tell you exactly which specific materials or products those are,

I am unable to access external URLs, so I cannot translate the text from the provided link. Please provide the text directly, and I will be happy to translate it for you.
Last download, sheet MWB overview.

Hello everyone,

I have now conducted two more measurement runs. In one run, I logged data for parameters MWB 1, 2, and 10. In the other run, I logged data for parameters 1, 4, and 10. I hope that these are the correct values you were looking for.

During the tests with engines 1, 4, and 10, I also performed a full-load acceleration test and analyzed the results in a diagram. It's evident again that there's an issue with the air intake. Both the MAF sensor and the intake air pressure briefly drop around 1300 RPM, just like in my previous logs. However, the fuel injection quantity appears to be good based on its curve.

In the second diagram, I have depicted a typical acceleration scenario with gear changes. Unfortunately, I lack the experience to properly interpret this diagram.

I have attached the relevant log files as an Excel file. Perhaps you could take a look at them and provide your assessment.

Unfortunately, I still don't understand why the intake air pressure is dropping or fluctuating so much around the target value. Do you have any other suggestions for things I should check?

Regards,
Steffen.

I would once again check the vacuum system for leaks and look for any foreign objects/obstructions in the intake manifold and exhaust system.

Hello,

I just completely disassembled the entire vacuum system again and installed the absolute minimum setup with brand new vacuum hoses. The only components that were installed were: the N75 solenoid valve with 3 new vacuum hoses to the air filter, to the vacuum hose of the tandem pump, and to the VTG (Variable Turbine Geometry) sensor. The N18 (exhaust gas recirculation cooling switching valve), pressure accumulator, and check valve were not installed! Since I had already swapped the N18 and N75 previously, I want to completely rule out any issues with the vacuum system now.

Regards,
Steffen.

Steffffen wrote:

Since I had already swapped the N18 and N75 valves before, I want to completely rule out the vacuum system now.

As I mentioned earlier: either something is mechanically stuck, or something has too much play.

Hello everyone,

There are new developments again. Unfortunately, I still haven't found the error. Recently, the following actions have been taken:

I took the car back to the workshop again to have it checked for the following issues:
- Intercooler circuit -> sealed/blocked.
- Vacuum system -> leak-tight.
- VTG adjustment --> "smooth and free of play, like new."
- Exhaust system blown through and not clogged.

The workshop's last suggestion was the turbocharger pressure sensor. I tried to replace it today, but unfortunately, it wasn't as successful as I had hoped. Because the two screws were very rusty, I treated them with WD-40 and let them soak overnight. Despite being careful, both screws broke off. The remaining pieces can't be unscrewed from the plastic of the intercooler, even with a large pair of pliers. Does anyone have any ideas on how to get them out? Temporarily, I secured the new sensor with one screw by wedging it through one of the other holes in the sensor. However, even with the new sensor, the behavior hasn't changed. I'm really at a loss now.

Currently, I'm noticing that the car pulls noticeably worse for the first few kilometers immediately after starting up in extremely cold temperatures. The fuel consumption during acceleration remains much too high.

Where can I continue searching for the error? Could it possibly have nothing to do with the boost pressure, and are the boost regulation problems just a secondary issue?

Thank you in advance for your help.

Regards,
Steffen.

Steffffen wrote:

VTG adjustment --> "smooth and free of play, like new".

Did you also disassemble the loader and check if all (!) VTG blades move simultaneously when the external lever is activated?
If not, excessive play can still be the cause of the turbocharger surge.

Quote:

Currently, I only notice that the car pulls noticeably worse for the first few kilometers immediately after starting in very low temperatures.

The fuel consumption during acceleration remains much too high. } Then, log MWB values 3, 8, and 11 simultaneously during the problem phase, without any interruptions.
I know this will be a huge log file, but in my opinion, you can't get anywhere with just small, individual logs when dealing with this type of question.

Hello Ulf,

Regarding the statement about the VTG adjustment being "smooth and free of play," I unfortunately can only refer to the workshop's assessment. I would have liked to be present during the entire inspection, but I was not allowed.

What do you mean by a test drive with engine loads of 3.8 and 11? Also, a full-load acceleration test? This is described in my very first post, which is attached. Since the problem of excessively high instantaneous fuel consumption during acceleration persists and doesn't just occur sporadically, it was also present on this particular trip. Furthermore, the engine speeds remain unchanged.
If a different route is required for this, I'll have to wait a bit longer until the snowfall stops.

Regards,
Steffen.