ARL Engine Problems: Troubleshooting & Repair

Hello,
I drive a Golf 3 TDI that I converted about 2 years ago with the "big" PD TDI engine, with the engine code ARL. My pride and joy has been running very well so far, but now it's having problems. The mileage is approximately 60,000 kilometers.

"When accelerating, there is a lot of black smoke coming out, and the engine has less power; the loss of power isn't extreme but noticeable. Furthermore, the amount of black smoke increases with higher RPM, and the engine feels sluggish. This is accompanied by a distinct hissing/whistling sound coming from the engine compartment. Fuel consumption is only slightly increased."
I already replaced the air filter, but it didn't solve the problem, just like cleaning the mass airflow sensor (which was replaced about 10,000 kilometers ago). There are no new error codes in the engine control unit (there aren't any new ones because my ABS speed sensor on the rear right is defective...). I checked the EGR valve on the "cold" side and found only a small amount of deposits, which I removed. The valve itself was also moving freely. I visually inspected the pressure hoses, but they seemed to be okay at first glance, as did the intercooler pipes (as far as you can see). I also took it for a test drive and logged the data using VAGCOMM (measuring blocks 03, 08, 11), which you'll find in the attachment. I can't fully interpret these values, but I think the boost pressure of 2.5 bar during the two full-throttle phases from 2000 to 4100 RPM seems normal, and I hope the turbo isn't the culprit (it's very expensive...).
Next weekend, I plan to remove the low-pressure coolant hoses and pressure hoses for a thorough inspection (and cleaning if necessary), and also disable the EGR valve. How can I inspect the large low-pressure coolant hose that's located in front of the water cooler? Do you have any other suggestions?

Greetings from the North.
Olli [/list]

How can I attach the file (the log) here? If that's not possible, I'd be happy to send it to you by email.

Hmmm....

'Knocking' usually indicates insufficient boost pressure. The hissing sound you described is another indication of this. A visual inspection alone is generally not conclusive. Even if your boost pressure eventually reaches 2.5 bar absolute, that doesn't necessarily indicate a functioning turbocharger or intact charge air system. Look for the 'leak' and check the free movement of the variable turbine geometry (VTG).

Otherwise, the technical article on performance degradation will likely be helpful as well.

Okay, I will definitely do that. How can I check the ease of operation of the VTG (Variable Turbine Geometry)? Could you possibly identify something from the VAG log data? Would I be able to email it to you?

Here you'll find a lot of information for testing the VTG (Vehicle Train Monitoring System). You can either find it in the articles or using the search function. Why send logs via email? If you take measurement block 11 and use value 2 (target) and value 3 (actual), and create a chart with something like Excel, you'll see for yourself what's going on.

Hello Olli,

'Firstly, the boost pressure is certainly not 2.5 bar, but rather a maximum of around 1.5 bar! Furthermore, the hissing sound, as already mentioned, is a clear indication of a leak in the charge air system.'
The methods for checking the ease of operation (VTG) have been discussed countless times and should be straightforward after studying the relevant articles. Please don't take it personally, but these topics have already been discussed extensively here. If you have any questions about understanding something, we are happy to clarify them.

Let's start: https://community.dieselschrauber.org/en/viewtopic.php?t=3004

Have fun! / Enjoy the rest of your time.

"I don't want to bother anyone here with questions that have already been asked. I will also be conducting further tests over the weekend. I was just hoping that someone might be able to take a look at the logs, as I am new to this and would like to learn from an experienced user. I'm not too lazy to implement any suggestions given. I thought maybe we could extract more information from the logs. I have modified my car, and the engine noise and the turbocharger sounds are much louder and more intense in the Golf 3 compared to the well-insulated Golf 4. It seems like the whistling sound has gotten louder, although that could just be my imagination. When you're dealing with a problem, you start questioning things (was it always like this, or is it only happening now?). Checking the intake system and the turbocharger probably requires removing the engine, at least as far as the turbocharger is concerned, because the engine bay of the Golf 3 is somewhat smaller than that of its successor. And if there are any other clues in the logs, I will definitely check those first. I have already looked at some articles here on the forum and compared them to the target values, but I'm having a bit of trouble because I can't find those target values specifically for the ARL engine."

Hello,

Okay, please share the log file with me, and I'll post it here. But please don't format it as a column of random numbers.

I just sent it to you via private message.

Here's the log, initially without any further analysis:

Oh my god, this mess of numbers.

Please review Group 11, values 2 and 3! You never reach the target value above approximately 2000 RPM. Additionally, you are experiencing extreme overshoots during 'deceleration.' Therefore, please check the VTG (variable turbine geometry) and the tightness of the charge air system, including the intercooler! In my opinion, the mass airflow rate is okay.

'Edit: It shouldn't be the VTG. The hissing sound contradicts that.'

Hello Zak1976,
If you hear hissing coming from the engine compartment, there's likely a leak somewhere after the fuel tank (ATL). This should be noticeable when accelerating while the vehicle is stationary.
Best regards,
Günther.

First of all, thank you for the response. After some thought, I also suspected a leak between the turbocharger and the EGR valve, or a faulty boost pressure regulator, but that doesn't seem to match the measured values.
Do you have any tips on how I can specifically check the large language models (LLMs), other than a visual inspection?

A leak in the intercooler system is usually detected by the presence of oil mist at the leaking point.
It is also possible to seal off the charge air path after the turbocharger's compressor up to just before the EGR valve. Simply insert a tightly sealing plug into the piping after the turbocharger. Similarly, connect it from the direction of the intercooler just before the EGR valve. However, install a tire valve in this plug and then pressurize it with an air compressor to 2 bar. If this pressure drops within, say, half an hour, then your charge air path is leaking. (Caution! Pay attention to pressure equalization!!) Otherwise, it is likely due to an EGR valve that is not sealing properly.

But even in this case, the search function could have helped you.

How can these significant "deviations" be explained when there's a sudden "loss" of acceleration (e.g., due to a leak)? These are sometimes deviations of almost 100%??????????

Hello,
It can originate from the characteristic time constant of the VTG adjustment.
Best regards,
Günther.

Due to the more aggressive control of the VTG (Variable Turbine Geometry) used to achieve the target boost pressure, the turbine blades are positioned quite steeply in the exhaust stream. Consequently, it takes a certain amount of time during 'descent' (reducing power) for the blades to be repositioned within the exhaust stream so that the target boost pressure is reached again. This somewhat sluggish behavior also depends on the characteristics of the exhaust flow. However, these overshoots are present in such systems. If your intercooler system is working correctly, you will likely still experience similar overshoots. Probably not as severe. Also, you will certainly be able to observe overshoots when adjusting the maximum boost pressure.