Turbo Problem: Low Boost? Troubleshooting Guide

Hello!

The neighboring workshop called me in for 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 at idle, you can even see the charge air hoses slightly contracting.

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

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 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 operational.
Actuator diagnosis for the turbocharger pressure control is working.

The intercooler 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 wires were resoldered.

Connecting a vacuum pump to the turbo pressure sensor will work.
but somehow, the path that the linkage takes seems...
"There seems to be a bit too much material here... I'd estimate about 2 cm. Is there something wrong? Perhaps it was assembled incorrectly?"


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

Yes, now good advice comes at a high price.
I also had the idea of somehow looking inside the turbine to see if the guide vanes are actually moving.
But I suppose you can't see that.
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? Rag left inside? Catalytic converter blocked?

mullemaus wrote:

Air filter on? Rag left inside? Catalytic converter blocked?

HI!

Okay, the air filter is new.
There's a pad in there, I'll check tomorrow, but I don't think so.
and the exhaust was broken during the test drive.

Is the vacuum also present at the VTG? Is the N75 working? Check the timing while driving. If it's statically at its maximum value (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.
It was around 24% at partial load, and close to 50% at full power.
The accelerator pedal went from 0% to 100%.

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

Hi,
Are the hoses already constricted when the engine is idling? Should they be placed 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.
Und zwar an den oberen Ladeluftschläuchen, die gut zugänglich sind. NAfter the LLK.

The hoses on my wife's golf cart were bulging quite a bit.
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; the neighbor assured me of this.
"But I can double-check it myself tomorrow."

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

It's roughly like blowing air through the 20 cm long lower turbocharger boost 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 get sucked in? Then you would have the same effect.

Hi,
- Completely check the airflow system, from the air filter intake pipe to the intake manifold. Something might be blocked or constricted there.
- Check VTG/loader settings according to the technical article.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.
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...
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, actually.
I'm not entirely sure, though. I haven't measured it.

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

The VTG (Variable Transit Gauge) is usually correctly adjusted for this type of tank car when slightly loosened screws on the VTG housing cause the adjustment rod to be fully extended, and the lever is thus at the "up" stop. In other words, the stop of the adjustment in the tank car corresponds almost exactly to the fully extended adjustment rod.

Best regards, Rainer.

Hi Steffen,
Just to be absolutely sure, you measured approximately 1.3 bar of boost pressure during the test drive, and in addition, you observed a vacuum of 250 mbar 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 also only fluctuated slightly. Perhaps around 20% downwards.
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, using my laptop as a sort of co-pilot, I took a look at 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" comes to mind spontaneously. Are the air volumes generally plausible?