Turbo Problems: Overboost Explained

Hi,

Today was another terrible day. First, the clutch started slipping constantly in 5th gear. Then, while overtaking, the car suddenly went into limp mode. I turned the ignition off and on again... and then I was able to overtake again.
At home, the error code 17965 (charge pressure control, limit exceeded) then becomes apparent.
In the log, I can actually see that the boost pressure holds above the 1.5 bar mark for 4 seconds, then gently drops to the correct 0.9 bar. However, the car doesn't go into limp mode or generate an error message after just 4 seconds. It only activates limp mode after 6 seconds (which was difficult to simulate).
That was new to me. I thought the threshold should be much lower. You never stop learning.

Well, Bertil, none of this would have happened if we had used biodiesel *hides*

SeatArosa1.7SDI wrote:

Well Bertil, none of this would have happened if we had used biodiesel *hides*

Okay, I understand. Please provide the German text you would like me to translate into English.
Then I wouldn't have just had one weasel in the engine compartment, but a whole horde... so the hose would have been completely gone .



The hose to the VTG (Variable Turbine Geometry) had a tiny hole, which caused a slight delay in the boost pressure regulation.
However, there's also a positive side to this. Now I understand why the AXR doesn't smoke. The high boost pressure for about 4 seconds is normal. My neighbor's AXR also exhibits this behavior. So, the AXR is supplied with extremely high boost pressure during the acceleration phase, but with very little fuel.

By the way, the VTG is incredibly smooth and easy to operate.

Hello Bertil,

Did the clutch slip only because of your '6 sec. tuning = 1.5 bar boost ', or were there other causes?

How many horsepower did you have temporarily, and what does the 'butt meter' say?

Best regards, Georg.

Hmm, if less diesel fuel is being injected, where is the extra power supposed to come from? The improved combustion due to higher boost pressure certainly won't be the reason.

Georg-TDI wrote:

Did the clutch slip only because of your "6 sec. tuning = 1.5 bar boost

" setting, or were there other causes?

Quote:

The clutch has been intermittently losing power for some time now. Previously, the cause of the problem was not always clear, but now it is. How many horsepower did you have temporarily, and what does the "butt meter" say?

Quote:

No performance improvement detected (reasoning below).

Hm, if less diesel fuel is being injected, where is the corresponding increase in power supposed to come from? The improved combustion due to higher boost pressure certainly won't be the reason for it.}

The trick here is that the temporarily increased boost pressure isn't about increasing performance, but rather about reducing smoke (and thus reducing emissions under EU4 standards).
I've now carefully reviewed the old boost pressure logs and noticed that my AXR engine (when accelerating fully) has been running at 1.5 bar for a few seconds, then dropping back to around 1 bar. This is probably the reason why I have a GT1749V turbocharger on my AXR engine. In theory, it should be too large for my engine. However, since it's operating for a short time with the boost pressure of a 96kW engine, a more stable turbocharger is needed.
That could also be the reason why some people find the 74kW engine (especially the AXR) to feel weak in the higher RPM range. It's amazing what all is being done to minimize emissions. In any case, a lot of air is being "pumped in" to keep the emissions as low as possible.
The AXR barely produces any smoke. Now I understand why.

Hello Bertil,

Did the WoWa (water pump) operation have any noticeable effect on the clutch's lifespan?

Marco wrote:

Hello Bertil, Did the WoWa operation become noticeable based on the clutch's lifespan?

I cannot answer that with a simple "yes" or "no."
The clutch has only been in use for just over 77,000 kilometers, which is definitely too low.
"However, I know of several AXR drivers who have experienced clutch problems, so I suspect the component is undersized. Unfortunately, VW has rejected a goodwill claim."
In the Wowo operation, the clutch never lost its engagement, only when operating in solo mode.

There are also indications that the clutch hydraulics may be involved.
Interestingly, the slipping problems almost exclusively occur during the winter months and then usually only when the engine is cold...

Here are the experiences of other owners of 74 kW vehicles; hopefully, this information will help you with the (often granted) concessions.
Attention, 98 posts ...

http://www.michaelneuhaus.de/php/forum/golf/entry--2-81385-1.htm

Or an expression from the thread, or from the many other threads you'll find by searching for "clutch" there. You can also post without registering if you have any questions.

Roger wrote:

..... Here are the experiences of other owners of 74 kW vehicles; perhaps this information will help you with the (often granted) goodwill gestures. Attention, 98 posts ...

I'm familiar with that thread, but those are far from being all of them.

It's worse in the winter than in the summer, but even with the slightest amount of modification, the clutch slips (even in the summer).
In my case, the clutch starts to slip after about 20 km of driving. However, there are no problems on longer journeys. }

Hi there,

@Bertil, great signature and awesome avatar. I just hope that...

Do you think your conclusions regarding boost pressure and its regulation are correct? I don't necessarily agree. We've had several similar cases recently, but in those instances, the boost pressure issue was different.

Here are a few thought-provoking ideas:
- adhesive pressure container
- faulty or sticking wastegate valve.
- but jerky VTG movement.

I can't tell you much about the clutch. I would put pressure on VAG (Volkswagen Group) accordingly, and I'm sure that will also lead to a good resolution with them.

Well,

After a few failed attempts, I'd like to provide the solution to the problem now.

To begin with, this problem was not mentioned in any scientific articles, and it also consisted of several issues.

Initially, I suspected a stuck variable turbo geometry (VTG) unit, but that wasn't the issue. The boost pressure control valve also wasn't the problem. However, after a test drive, as I parked the car in the garage, I heard a crackling noise after a while. What was that? After some searching, I discovered that the vacuum actuator for the VTG was stuck in the maximum position. Something (possibly oil residue) was preventing it from returning to its normal position. However, if you manually move the linkage, you can't detect this fault.

Okay, so the boost pressure was reduced more quickly, but the overshoot of 1.5 bar remained.
Where else should I look?

I was also able to rule out any apparent vacuum issues.

Aus Frust hab ich dann meinem Frisch gereinigeten K&N Luftfilter gegen einen alten Papierluftfilter getauscht und siehe da .... der Ladedruck verhält sich wieder völlig normal! .... WWhat was that?
When I disassembled the filter, I discovered that it was completely full of concrete. A few weeks ago, I drove through a cloud of dust near a cement factory. I got paid for a car wash, but I didn't think about the air filter. The cement mixed with the filter oil (and possibly some humidity) to form a concrete-hard mass, significantly reducing the airflow.

I've experienced some air conditioning issues before, but never anything like being cemented in... that was my first time.

EDIT:

A request for goodwill coverage for the clutch is still being processed.

An interesting facet. But probably too rare to be included in a specialized article .

Can concrete also get into the VTG container, perhaps through the "oil smear" you mentioned?

Roger wrote:

.... Can concrete also get into the VTG container - the "oil smear" that you mentioned?

No, it was definitely resin-coated. Concrete doesn't get resin-coated .

Bertil wrote:

However, after parking the car in the garage after a test drive, I heard a crackling sound after some time. What was that? After some searching, I discovered that the vacuum actuator of the VTG (Variable Turbine Geometry) was stuck in the maximum position. Something (possibly oil residue) was preventing it from returning to its normal position. However, if you move the linkage by hand, you cannot detect this error.

Hi Bertil,

what all there is... what exactly did you observe that made you determine that the "adhesive" is in the can and not in the turbine housing?

By the way, if we broaden the definition of "VTG" to include the actuation mechanism, specifically considering the can as part of the VTG, then I believe it is indeed covered by the technical article.

In
I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the text from the URL you mentioned, and I will be happy to translate it for you.
it is explicitly pointed out that the cans may be stuck .

ulf wrote:

what all there is... exactly what did you observe that made you determine that the "adhesive" in the can is located and not, for example, in the turbine housing?

The rod can be easily checked for free movement mechanically. In my case, it moved freely from end to end.

While the engine is idling, disconnect the vacuum hose from the control valve (N75). With a mechanically fully functional VTG system, the control valve should immediately return to its default position (minimum boost pressure). However, if the control valve is stuck, it will remain in the maximum boost pressure position for a period of time.
The error can only be reproduced under vacuum conditions!

Quote:

If we broaden the term "klememnde VTG" and include the actuation mechanism, considering the "can" as part of the VTG, then, in my opinion, it is indeed covered by the technical article . However, it might not hurt if, instead of the actual VTG mechanism, the can itself also gets stuck.

The can didn't get stuck, it was glued. Flushing it with alcohol solved the problem. A lot of black/brown sludge came out.
Unfortunately, I don't have a schematic diagram of this device, so I can't form a clear picture of what happened.


You didn't mention the concrete-covered Lufti anywhere ... it's probably more of a rare occurrence...

Bertil wrote:

The can didn't get stuck, it just got glued. Flushing it with alcohol solved the problem. A lot of black/brown sludge came out. Since I unfortunately don't have a schematic diagram of this device, I can't form a picture of what happened.

Schitt model is good .

Is there, in fact, any theoretical possibility of how oil could get into the AXR container (assuming it's not due to manufacturing residues)?

"In the case of the AFN, ALH, and ASZ engines, I believe this issue only occurs when the engine is stationary, as oil vapor from the crankcase is drawn backward through the pump and gradually seeps into all parts of the pneumatic system."
However, I assume that the vacuum pump "disposes" of the air drawn in by discharging it into the crankcase.