Golf 4 Performance Issues: 110 HP Pump Denoise

Hello!

I currently have a Volkswagen Golf with a 110 HP PD engine (engine code AJM) that has a rather interesting problem.

Error codes read, none found. EGR valve checked mechanically, it's working correctly.

The car drives, but with maybe only 70 horsepower or so. What's interesting is that if you floor the accelerator while driving, you feel a brief, strong push into your seat – you notice the 110 horsepower. But then, about a second later, it feels like someone is pulling the handbrake. It then continues to accelerate very slowly until the rev limiter. If you let off the gas and then press the accelerator again, exactly the same thing happens.

'Is there a similar type of regulating valve like in the 1Z engines that might be incorrectly reducing the boost pressure? It seems that way, but then there should be something stored in the error memory, right?'

Measuring injection timing doesn't really make sense for direct-injection engines, does it?

Greetings.

Hi,

If it's an AJM engine, I would first look for the missing 5 horsepower... because it should have 115 hp.

Just kidding.

You can find information on how to check the injection timing in Ulf's article. In the case of a PD (likely referring to a specific type of engine or system), all adjustments are made mechanically.
A pressure test would be a good idea. Ideally, even a complete test drive with a measurement protocol.

Then, check the turbocharger's variable geometry turbine (VGT) for proper operation (it tends to get stuck), and perform Bertil's suggested test drive with a boost pressure measurement. It seems the boost pressure is too high, which then causes the engine to go into limp mode.
However, this should already be recorded in the file system. Perhaps you read it too late and he deleted it. (Is that a feature of the software?)

Another case for CLICK.

Hi!

'Thank you, I was able to identify the problem. During a test drive, it immediately became apparent that when full throttle is applied, the boost pressure suddenly jumps to 2800 mbar, whereas only 2250 mbar is required. This will likely cause the control unit to enter limp mode. However, I'm surprised that no error code has been stored in the diagnostic memory.'

Can someone tell me where the corresponding control valve is located in a Volkswagen Golf 4? I'm familiar with it from the 1Z models, but I haven't seen anything that looks similar.

Greetings and thank you!

... try searching for "VTG that's stuck"; you'll find your error 99% of the time... Julian already mentioned it! The control valve is almost certainly not defective.

/viewtopic.php?t=2992&highlight=stuck+VTG

Hi!

Okay, I just used VAG-COM to alternately activate the control valve and observed the rod movement, which worked perfectly, moving smoothly from minimum to maximum. I also connected a large syringe and pumped it back and forth a few times, sometimes with less force, sometimes with more. Everything seemed to work fine; there was no sticking or anything like that, so unfortunately, it probably isn't the rod itself.

However, the valve doesn't seem to be doing anything either; otherwise, it probably wouldn't have been able to function in a wave-like pattern according to VAG COM rules.

Very strange... Does anyone have any other ideas why the car suddenly goes into limp mode after the turbo pressure spikes?

Thank you.

I also checked the LMM (mass airflow sensor), installed a new one from a Passat PD (also with the AJM engine), but there's no difference.

Greetings.

Can you measure your boost pressure using an analog gauge and compare it to...?
Comparing MSG values.
Maybe it's slightly defective!

Bin heute mal etwas länger Autobahn gefahren, er kommt max. auf 170 km/h, allerdings ab ca. 140 km/h nur noch 'Schubweise'.. It's really weird...

You can feel the turbocharger building pressure, then it seems to go into limp mode, hesitates for 1-2 seconds, then the pressure comes back, and it goes into limp mode again, needing its 2 'thinking' seconds, then the pressure returns... It's really strange.

Hi m3nx,

I don't think this has much to do with the classic 'emergency mode.' That usually only activates after a reboot of the car. It seems more likely that the control unit is trying to compensate for excessive pressure surges in the turbocharger in a very aggressive way. As can be read in other threads, a variable turbine geometry (VTG) turbocharger can sometimes exhibit erratic behavior. Therefore, I suggest not just analyzing the boost pressure with a test drive, but also logging all other parameters.

- LLM values including the duty cycle of the solenoid valve.
Boost pressure.
- Fuel injection quantity, including fuel temperature.

Furthermore, I would definitely take a close look at the AGR (Abgasrückführung system) and temporarily disable it for testing purposes.

Hello m3nx!

The cause of your problem is likely a faulty VTG (variable turbine geometry), even if the actuator diagnosis was successful.
When there is a significant overboost in the charging pressure, the engine control unit (ECU) drastically reduces the fuel injection amount to reduce the mechanical stress on the engine. This has the effect of being like someone engaging the handbrake.

At what temperature did you perform the actuator diagnosis? It's possible that the hesitation only occurs at very high coolant temperatures. Try performing the test with a cold engine, then with the engine warmed up after a few minutes of idling, and finally with the engine hot after some time running at full throttle. This might help you identify the cause of your problem.

Regards,
Alex.

Hi!

'Thank you for the tips. I will now re-check the jerky behavior of the VTG by performing a test run with logging and graphs. I will check the mentioned parameters such as mass airflow rate, control valve, boost pressure, etc., and then report back.'

Greetings.

Hi!

Okay, the VTG (Variable Turbine Geometry) is definitely malfunctioning or can no longer be controlled precisely enough. Under full load, the boost pressure exceeds the target by about 300 mbar, then it's reduced, then it increases again, and there's another overshoot... This keeps happening repeatedly. I'm now going to try cleaning and lubricating the control rod somehow.

Hopefully this will work, because it actually worked quite well using vacuum or a suction pump... I'm very surprised that the solenoid valve can't achieve the same result.

Greetings.