LD Vacuum Leak: 890mbar Idle, No Pressure?

'Hi, recently I haven't been able to reach the target boost pressure of 2250mbar (chip), but only around 2050-2100mbar. At idle, the pressure is only 890mbar. The turbocharger whistles as usual, and I haven't noticed any increased play, but I'll check that again tomorrow. Can I assume that my turbocharger is slowly failing? I can hear a faint, indefinable noise under full load, but it only occurs when driving at full throttle.'
I'm a bit lost, as I was actually planning to go on vacation soon.


Best regards, Dr. B.

What about the search function?


'Is the intake manifold okay? Is the boost pressure line sealed? With the engine off, is the ambient air pressure the same as the boost pressure?'

That's just the standard program...

..oops sorry, I didn't write that down. The mass airflow sensor (LMM) is fine, I checked the turbocharger pressure system as best I could, but unfortunately, I couldn't rule it out. Nothing is misaligned on the VTG (variable turbine geometry) rod, and the linkage is easy to move. I can't understand the issue with the vacuum at idle; it wasn't like this before, and I haven't found anything about it in the search.

What does a diagnostic system report regarding ambient pressure and boost pressure when the engine is not running? The values for ambient pressure and boost pressure should be relatively close to each other in this situation. If they are not, the boost pressure sensor may be defective.

How do you measure 8xx mbar?

How about you tell us a little more: mileage, condition, etc.?

Hi!
Negative pressure while the engine is running usually indicates intake problems -> is the air filter okay? Or is the air supply clear?

Best regards,
Dirk.

hello pretzel,

I've also thought about that. But first, we need to address the other issue... However, it could also be as simple as a problem with the pressure indicator.

'So, I just took another measurement and did a test drive. Even when the engine is off, the difference is around 90 mbar, meaning it's only 890 mbar. The LLM (likely referring to a specific engine parameter) goes up to 1250 at full load and around 3000 RPM, and about 450 at idle. Oh, and I read all the boost pressures using Vagcom, but unfortunately, I don't have a reference value from a Lambda sensor or anything like that. How can I test the pressure sensor in the engine control unit (ECU)? What else could it be?'

Thank you for your quick help!

It either looks like a clogged 'measuring hose' or a faulty sensor.

'I'll check the hose from the pressure pipe to the wastegate tomorrow. Is there a way to test the pressure sensor? What kind of sensor does the AFN engine have, 250 kPa? The pressure sensor also seems plausible because of the vacuum at idle. If I add the missing 90 mbar to the maximum actual pressure, I get close to the target pressure. Shouldn't the turbocharger compensate for that, though?'

You can find the Bosch part number on the sensor... Is it already located in the control unit?

Okay, maybe. If the sensor stops measuring, then no... In that case, the manufacturer can place the probes anywhere they want in the exhaust stream. It won't matter anymore.
Warning: Excessive stress could lead to turbocharger damage.

'Yes, the pressure sensor is located in the control unit. To determine if the sensor itself is the problem, would using an LDA (Linear Density Analyzer) as a reference be helpful? Or is the tolerance of the LDA too large to clearly read the difference? Do you happen to know approximately how much a pressure sensor costs? Could it still be something else? At what percentage does the duty cycle become unhealthy?'


Best regards, Sebastian.

dr_braun wrote:

..yes, the pressure sensor is in the control unit. So, to find out if it's the sensor, would using an LDA (Linear Density Analyzer) as a reference be helpful? Or is its tolerance already too large to clearly read the difference? Do you happen to know approximately how much a pressure sensor costs? Could it still be something else? From what percentage is the duty cycle unhealthy? Best regards, Sebastian

90 mBar is a bad reading; it indicates either a contact problem or that one of the two pressure sensors is faulty.

The duty cycle should not get stuck at the extreme values during normal operation. This indicates potential mechanical jams or other inconsistencies in the control loop.

Best regards, Rainer.

'nda' is always a good idea...

I can't tell you how much that part costs. But it definitely can't be a global product. Also, I think there might be problems with sourcing parts from ET (presumably a parts supplier). You can probably forget about VW. Bosch might be an option, but only if the workshop/dealer has a good selection.

Otherwise, it could be many things. But, as you mentioned, most of it has been checked and found to be satisfactory.

@Rainer:

'Are you referring to the three solder joints in the control unit when you talk about contact problems? The pressure of around 90 bar can be observed throughout the entire speed range, except that around 2000 rpm, it reaches 2250 bar, and that value is then also displayed? That's quite strange.'

Hi,

just to be sure:

The 90 mbar difference in the boost pressure sensor reading could also be a sign of a malfunctioning chip tuner that is unable to increase the boost pressure in any other way... -> 10c boost pressure tuning.

Can you rule that out?

Or, have you ever read boost pressure and ambient pressure as (almost) the same values after chip tuning, with the engine idling?

@Ulf:

'I can't completely rule that out, as I didn't measure these values with the engine idling. The target pressure has been increased to 2244 mbar, and the car was running really well, significantly better than the previous chip. I only installed this ECU last Thursday, and the LD problem started since last weekend (Sunday). Unfortunately, I don't have a second ECU available, and I'm planning to go on vacation next week (over 2500 km), so everything should be okay then, so I don't get stranded abroad .'



Thank you again for your help!