Turbo problem, barely any boost

Hello!

The workshop next door called me in for some help today.

The problem car is a VW Passat Variant with a longitudinally mounted 1.9 TDI engine (code AHH).
TSN: 0603 359
Year: 1999
Approximately 200,000 km.

The problem is a lack of engine power.
Very little boost pressure is building up. When observing the engine running while it's stationary, you can even see the intercooler hoses slightly contracting.

The master mechanic from the workshop next door isn't actually stupid.
"But today, they spent the entire day working on the car, and I believe they were already working on it before that as well."
fought against it.

A few weeks ago, I adjusted the start date of the funding, as he requested, but, as expected, it didn't make any difference.

LMM has likely been replaced several times (only the sensor itself).
The turbocharger has now been upgraded, and a small company near Dresden has repaired/reconditioned it.
but it didn't achieve anything.

We took a test drive together today.
and I took a look at the values:

First: The error memory is empty.

LMM can go up to a maximum of 800.
Boost pressure up to 1.3 bar.
VTG container and support structure are in operation.
Actuator diagnosis for the turbocharger pressure control system is working.

The charge air cooler is clear.
The turbo is spinning.

Driven without the exhaust, no change.

Furthermore, some kind of "tuning box" was connected to the mass airflow sensor (MAF), which was removed, and the cables were re-soldered.

Connecting a vacuum pump to the turbocharger pressure sensor will work.
but somehow, the path that the linkage takes seems...
"It's a bit too long... I'd estimate about 2 cm. Is there something wrong with it? Maybe it was assembled incorrectly?"


We ran the engine in the workshop.
with a capped hose at the turbocharger outlet.
"So, not much air actually came out... Even when I floored it, I mean, normally I would expect that to kick up some dust in the workshop, but it really didn't."

Yes, now good advice comes at a high price.
I also had the idea of somehow looking inside the turbocharger to see if the guide vanes are actually moving.
But I suppose that's not obvious.
Otherwise, the engine appears to be in good mechanical condition, starts easily, and sounds good.

Does anyone have a suggestion on how to proceed?

Air filter on? Did you forget to put a cloth in? Is the cat okay?

mullemaus wrote:

Air filter on?

Cloth left inside? Is the cat closed?

HI!

Okay, the air filter is new.
Something is stuck inside, I'll check tomorrow, but I don't think it's there.
and the exhaust was detached during the test drive.

Is the vacuum leak also present at the VTG? Is the N75 valve working? Check the timing while driving. If it's statically stuck at a high level (4.x...99%), then something is wrong .

Hi!

Yes, the vacuum sensor is working.

During the test drive, I checked the control for the turbocharger boost pressure valve (or something like that).
Okay, so let's talk about the time signature.
That was around 24% at partial load, and about 50% at full throttle.
The accelerator pedal went from 0% to 100%.

I can also perform a more targeted measurement run again tomorrow.

Hi,
Are the hoses already contracting when the engine is idling? Before or after the intercooler?
hg
Herbert.

Hello!

There's nothing to see when it's idling.
If you press the accelerator pedal while the car is stationary.
It is easy to see.
Specifically, it's located on the upper charge air hoses, which are easily accessible. After the LLK.

The tires on my wife's Golf were overinflated.
However, in the case of this particular car, it seems like the engine is drawing in more air than the turbocharger is pushing.

The intercooler intake path must be completely clear, and the neighbor assured me of that.
I can double-check it myself tomorrow, though.

but as I already mentioned,
It feels like not enough air pressure is coming out of the turbo.

It's roughly equivalent to blowing air through the 20 cm long lower turbocharger pressure hose using a standard workshop blow gun with its original nozzle, at a pressure of 3 bar. We tested it there as well, almost directly at the turbocharger outlet.
Not really much.

Could the intake hose from the air filter to the turbo potentially collapse? Then you have the same effect.

Hi,
- Completely inspect the air intake system, from the air filter housing to the intake manifold. Possibly, something is too tight or too loose there.
- Check VTG/loader settings according to the technical article:
Okay, I'm ready. Please provide the German text you want me to translate.
hg
Herbert.

Hello!

Thank you for your help!

I read in the link that the vacuum pressure at the can must be at least 600 mbar.
The value we measured during the test drive was a maximum of 250 mbar.

That's probably the cause.

I will report.

Steffen G wrote:

Hello! Thank you for your help! I read in the link that the vacuum pressure at the can must be at least 600 mbar. The value we measured during the test drive was a maximum of 250 mbar. That's probably the cause. I will report.

Hello Steffen,

However, the large adjustment range you specified doesn't seem to fit.
With only 250 mbar, I'd estimate it's about half the normal distance, so roughly 5-6 mm.

Best regards, Rainer.

Hello!

Thinking about it now, the large adjustment range seems excessive to me.
noticed,
when we tested the VTG with the engine idling, using a hand-operated vacuum pump.

While I was standing still with the engine running, I actually thought...
That's kind of a lot.
I'm not entirely sure. I didn't measure it.

And how is that?
If the vacuum pressure is too low, does the exhaust flow then push the guide vanes back?
or how am I supposed to imagine that?

Well, in any case, the vacuum needs to be fixed first.
before any more time and money is wasted.

Quote:

if the vacuum pressure is too low, the exhaust flow will push the guide vanes back. or how should I imagine that?

No, the vacuum closes the VTG, and if the mechanics are done correctly, it does so relatively independently of what is currently passing through the VTG.

Generally, the VTG (Variable Travel Gauge) is correctly adjusted for this type of load when slightly loosened screws on the VTG housing cause the adjustment rod to extend fully, and the lever is thus at the "up" stop. The impact point of the adjustment in the loader corresponds almost exactly to the fully extended adjustment rod.

Best regards, Rainer.

Hi Steffen,
Just to be absolutely sure - did you measure approximately 1.3 bar of boost pressure during the test drive, and also observe an additional 250 mbar of vacuum at the boost pressure control?
The duty cycle isn't at its maximum.
hg
Herbert.

Hello!

Yes, that's how it was.

There were 2 test drives.
the first one was connected directly to the turbocharger using a vacuum gauge.
I noticed the vacuum pressure was around 250 mbar, but I didn't take it too seriously at first.
The value has only fluctuated slightly. Maybe around 20% lower.
Nothing else happened.

The solenoid valve is new.

During the second test drive, another new mass airflow sensor (MAF sensor) was installed beforehand.
And then, I used my laptop as a sort of co-pilot and checked the values that I considered important.
Okay, so the maximum boost pressure is 1.3 bar, and the duty cycle of the magnetic control valve, as mentioned, is approximately 24% to just under 50% at full throttle.

"AGR" immediately comes to mind. Are the air quality measurements generally reliable?