1.4 TDI AMF: Turbocharger boost only from 2800 RPM

The following problem:

For the past week, my turbocharger has only been reaching its full boost pressure above 2800 RPM. Above 2800 RPM, the boost pressure curve is as it was before.

Here's what I've done so far:

The pressurized system was tested at 3 bar and no leaks were detected.

Checked the turbocharger boost hoses according to the hose routing diagram (I replaced the turbo about 20,000 km ago and wasn't sure if all the hoses were in the correct positions).

Intake manifold removed and turbocharger play checked - no play, all OK.

The LD control valve is supplied with 1 bar of compressed air without a running motor, and while doing so, the actuator diagnostics are performed – the wastegate rod moves smoothly.

LMM über Grundeinstellung 003 geprüft. 260 m. AGR 430 without EGR (Exhaust Gas Recirculation).

Disconnected the pressure hose from the turbocharger control valve. This disables the turbocharger boost control. The wastegate remains closed all the time. I noticed that the boost pressure starts building up at 2000 RPM, just like before. After that, it naturally increases and then drops off because there's no longer a limit on the boost pressure.

Test drive completed, and the following data was recorded:

MWB 008:
Torque limiting always provides the lowest value - which is normal.

MWB 011:
Should the LD (likely referring to a pressure reading) remain constant at 2244 mbar between 2000 and 3950?
Is the low-pressure area around 1050 millibars?
At an altitude of approximately 2200 meters, the air pressure is about 1250 millibars.
At an altitude of approximately 2600 meters, the pressure is about 1500 millibars.

I'm a bit at a loss right now. If I hadn't checked the LD control valve, I would have replaced it. But it turns out that the valve is fine.

Regards,
Thomas.

Please log 003-008-011.

"009 is uninteresting, but the air mass value (003) is important!"

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

I logged the LMM separately. If necessary, I can re-measure 003-008-011 in relation to it.
The LMM values are also too low up to 2800 RPM.

Regards,
Thomas.

Today I re-checked the wastegate using a warning light relay circuit. The wastegate opens when the pressure reaches 0.95 bar at the pressure sensor. I also checked an old turbocharger and it requires 1.5 bar.

For some reason, the engine control unit is opening the wastegate too early.

Is it possible that the hose routing diagram is incorrect? Currently, the hoses are connected as shown in the image attached. Could someone please confirm this?

Regards,
Thomas.

The connection looks okay - my single-phase AC unit also has the same type of hose.

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

'Cat broken - try hitting the cat enclosure with a hammer and listen for a hollow sound!'

Starting at a pressure of 0.95 bar in the pressure sensor, the wastegate opens. I also checked this on an old turbocharger, and it requires 1.5 bar.


'0.95 seems a bit high to me... after all, the boost pressure is regulated, so a reduced pressure is being delivered to the wastegate.'

It's already clear that the old turbocharger requires more adjustments, as it likely only uses a wastegate as a mechanical limiter, unlike your TDI which has an active control system. What car and engine is the old turbocharger from?

The pressure of 0.95 bar was measured without the engine running. When the engine is running, the exhaust backpressure helps to open the valve.

The old loader is exactly the same as the one that's currently installed. The wastegate failed right up until the end.

If I disconnect the hose from the pressure sensor, the pressure builds up as before. It's just that it builds up too much. Therefore, I don't really believe it's the catalytic converter. However, I will still check it. Unfortunately, the exhaust system from the turbocharger onwards is a single piece with no connection point.

Yesterday, however, things changed slightly. The turbocharger still doesn't provide boost until 2800 RPM, but then it suddenly builds up to 1.75 bar and maintains that pressure. The programmed map is set to 1.25 bar.

Furthermore, I'm just going to swap the connections on the control valve anyway. It can't get any worse than it is now.

Regards,
Thomas.

The control unit is programmed to a pressure of 1.25 bar.

aaaaahhhh - we're getting closer to the solution now... Do you have a tuning file installed?

Yes, of course. But I just realized that I forgot to mention it above.

Regards,
Thomas.

Was are you looking for?

'EDIT: Do you have a mechanical boost pressure gauge, or does VAG-COM display the values? It would be interesting to see what the comparison between ambient pressure and boost pressure shows when the engine is idling. If there are significant differences, it could be due to the turbocharger sensor...'

'Hi, the control unit has been soldered. I only have the tuning file stored in the control unit, nowhere else. However, the chip has been working perfectly for over a year.'

'There is a boost pressure gauge present. Otherwise, I wouldn't be able to tell if it currently has a maximum of 1.75 or 2 bar. The sensor only measures up to 1.6 bar.'

I have already checked the intake manifold pressure and ambient pressure. The values are plausible.

Regards,
Thomas.

I just checked on Kat. She sounds healthy and there are no unusual noises.

I figured out why it suddenly started regulating up to 1.75 bar. There's a small tube in the hose between the turbocharger and the control valve. Apparently, when I tried it without any boost regulation, that tube got pushed out. It popped out right at the level of a clamp that covers it.

It now regulates properly again, setting the pressure to 1.25 bar starting from 2800 RPM.

Now, the only question that remains is why it's opening the wastegate below 2800 RPM. There must be enough pressure for the wastegate to open; otherwise, it wouldn't open.

I've been thinking about it. It could be that the line leading back to the intake manifold is partially blocked. The pressure goes to the pressure sensor, the turbocharger control valve opens, but the pressure can't escape. Therefore, the wastegate remains open. Only at higher boost pressures can this restriction be overcome.

Maybe I'll disconnect the hose from the intake manifold later. Then it will just blow directly into the open air.
EDIT: Not working.

Regards,
Thomas.

How about the valve spring in the wastegate actuator? Could it be broken, which would cause altered regulation behavior (opening at lower pressure, automatic opening)?

Try moving it manually. It should be quite difficult, to the point where you probably can't do it (depending on how much strength you have).

By the way: soldering carries the risk that the solder joints may become detached ('cold solder joints').

Okay, so it was my turn again today. I filled the pressure regulator with spray oil, and also oiled the pressure rod and the wastegate itself from the outside. Then I replaced all the pressure hoses and resoldered the chip. I also checked the catalytic converter again on the lift, and it sounds full; there's no rattling.

I may look like a hairy beast right now, but it was worth it. The boost is fully engaged from 2300 RPM.
Sometimes it starts building pressure from around 2000 RPM, but sometimes not until 2200 RPM. In higher gears and when going uphill, the latter obviously causes the engine to go into limp mode.

Regards,
Thomas.

Quote:

Sometimes it starts building pressure from as low as 2000 RPM, but sometimes not until 2200 RPM.

In higher gears and when going uphill, the latter naturally causes the engine to go into limp mode. }

Huh?

Okay, I'll make it simpler:

With the engine running at full throttle, the boost pressure gauge starts to move from around 2000 RPM. The engine continues to rev up, and it reaches its maximum boost pressure just below 2200 RPM. However, sometimes the gauge doesn't start moving until 2200 RPM, and the full boost isn't reached until 2300 RPM. If you drive uphill in 5th gear at 2100 RPM, you might experience a limp mode because the desired and actual boost pressure are too different.

Regards,
Thomas.