Vacuum Measurement on 2.5 TDI Engine

Hello everyone,

Currently, I am troubleshooting a performance issue with my AKN.

In the basic control program 11 (boost pressure at idle speed), I am unable to achieve the target boost pressure even when the control signal is at 99%.
What was noticeable was a potential blockage in the VTG linkage. After assisting it with a screwdriver, I achieved the correct pressure.

A vacuum measurement, taken at a point between the check valve and the pressure transducer, showed a pressure of -450 mbar at idle speed.

Are the measured -450 mbar sufficient?

Greetings.
René.

From memory, that's not enough information. There was a thread recently where values were mentioned.
/viewtopic.php?t=10418&highlight=vacuum
I think the value should be similar for the AKN, and I'll measure it on mine later if I get the chance.

René_S wrote:

A vacuum measurement, taken at the measuring point between the check valve and the pressure transducer, showed a pressure of -450 mbar at idle speed. Are the measured -450 mbar sufficient?

No.

The topic has now also been included in a technical article about common mistakes.

I took measurements today: At idle, at the closed port just before the bypass valve (BKV), I measured 0.95 bar of vacuum, which makes me question the accuracy of the pressure gauge (Conrad).

I took measurements today: At idle, at the closed connection just before the BKV (Brake Control Unit), it was 0.95 bar of vacuum, which makes me question the accuracy of the pressure gauge (Conrad).

Hello Christians,

'I'm also seeing this value now, but without any downstream consumers connected. With the EGR and VTG connected, it's still around -800.'

It takes about 2 seconds for my air knife nozzle to reach a pressure of -800 millibar. This seems like a very long time to me...

However, 800 mBar should be sufficient. Mine has 500 mBar at the VTG sensor when idling, and a maximum of 600 mBar at full throttle with low RPM, but at that point, the VTG is already at its limit.

@René_S:
What type of pressure gauge are you using (from Conrad)?
I would also like to get one.

Hi,

A vacuum hose runs into the left wheel well.
There should be a pressure vessel located there (which is only visible after removing the wheel arch liner).
It often happens that the connection to the container comes loose, causing the pressure to drop.

Simple test: Use a hose clamp to pinch off the hose, then take a measurement.

Hello.

I checked this. I used the check valve located between the BKV (presumably a valve) and the pressure transducer. I connected the check valve, pressure gauge, and the hose to the pressure reservoir. After vigorously pulling on the RSV (presumably a valve or component), I observed a pressure of at least -0.5 bar.
A pressure drop could be used to detect a leak without having to disassemble the wheel and wheel well.

Good luck.
René.