Possible brake booster problem - vacuum leak - pressure test

[Primzy69]

I noticed a slight whosshing sound which stops as soon as you step on the brake pedal. Also brake pedal is a bit squishi...
I would like to confirm my thesis of bad brake bosster, can i somehow do a pressure test to see if i'am right?

Is it possible that due to vacuum leak in brake booster my MAF shows lower mass of sucked air? I read somewhere that the reading of MAF should be 10g/s at 3000RPM, mine shows only 7,8g/s. (2.0tfsi)

Not to mention struggeling with ruff ideling and vibrations for a while now.

[Primzy69]

Is it possible to somehow block vacuum hose to brakebooster and check my MAF readings if it is still the same?

[DaPlatypus]

Unsure about the diagnostic end, but if you are hearing hissing coming from the brake pedal shaft entering the booster and is completely silenced when applying brakes, your booster is going. Had the same thing happen to me.

[Smac770]

Your MAF has nothing at all to do with the vacuum system in a TSI.

There's six pages of procedure for testing the V192 brake vacuum pump as well as testing high and low pressure holding in the hydraulic system in the repair manual. Pay for a day at erwin.audiusa.com and grab the docs for your car. This particular one would be Repair Manual - Brake System.

You already have VCDS and did a scan? You're going to need VCDS to do the diag tests on the V192.

[Primzy69]

Your MAF has nothing at all to do with the vacuum system in a TSI.

There's six pages of procedure for testing the V192 brake vacuum pump as well as testing high and low pressure holding in the hydraulic system in the repair manual. Pay for a day at erwin.audiusa.com and grab the docs for your car. This particular one would be Repair Manual - Brake System.

You already have VCDS and did a scan? You're going to need VCDS to do the diag tests on the V192.

Are you sure about this, because when membrane in PCV was damaged, there was ruff ideling and because of that, engine is trying to compensate with different air/fuel ratio?
You mean testing by this procedure? : https://workshop-manuals.com/audi/a4...m_pump_-v192-/

I have VCDS and so far there are no faults.

[Smac770]

And the PCV is not tied to the vacuum system which powers the brake booster either. But the PCV is very tied to the intake tract.

If you have a vacuum leak, then diagnose that. If you have an intake leak, then diagnose that. But the vacuum system powered by the vacuum pump, which drives the brake booster and the intake manifold runner solenoid and the AC shutoff valve solenoid and the EVAP leak detection and such, doesn't cross paths with the intact tract. You can see the extent of the vacuum system here, https://www.audizine.com/forum/showt...m-Hose-Routing

The only MAF guidance I've ever read is 160g/s at high rpm at WOT. Are your trims lean or rich? Are you showing misfires (watch the live data counters, unless you're getting enough per 200 or 1000 revolutions, you won't get a DTC)?

[Primzy69]

And the PCV is not tied to the vacuum system which powers the brake booster either. But the PCV is very tied to the intake tract.

If you have a vacuum leak, then diagnose that. If you have an intake leak, then diagnose that. But the vacuum system powered by the vacuum pump, which drives the brake booster and the intake manifold runner solenoid and the AC shutoff valve solenoid and the EVAP leak detection and such, doesn't cross paths with the intact tract. You can see the extent of the vacuum system here, https://www.audizine.com/forum/showt...m-Hose-Routing

The only MAF guidance I've ever read is 160g/s at high rpm at WOT. Are your trims lean or rich? Are you showing misfires (watch the live data counters, unless you're getting enough per 200 or 1000 revolutions, you won't get a DTC)?

Ok, that makes sense. So it means that I have 2 problems...
I am almost positive that brake booster has to be changed.
I watched live data, but I'm not that good at resolving what they mean. So can somebody tell me if I read right things?






As you can see, short term was once negative and positive.
Thanks!

[Smac770]

Short term bounces around, that's it's job. Long term is what you would care about, and yours is under |5%|, so nothing to bother with there. No misfires. Might also check the knock voltages; like misfires there is a value for each cylinder so check all four values. No DTCs?
When you log (not watch unless someone else is driving :-) your air mass actual value during a floor it run, does it get up around 160g/s? Mine idles around 3g/s. But without an engine load value or something to designate how hard the engine is working at that 3k (just sitting there in park pressing the pedal vs climbing a hill), that 10g/s is not well qualified.
Could be a motor mount, carbon build up, dirty injectors, and those are just simple things I can envision.

[Primzy69]

Motor mounts have just been changed (both).
Could carbon be an issue that big? I think that it has never been cleaned. Gotta check...

What bother me after checking oxygen sensor (jump sensor) value is mostly standing at 0,64V, voltage of oxygen sensor (broadband sensor) value is standing at 1,436V. I also did the graph...

[Smac770]

Those seem normal for the engine under load. Just to be clear, do you have the 132kW CDNB or 155kW CDNC motor? Most here will have the 155kW CAEB, which is the NAR emissions version of the CDNC. Performance stats like WOT g/s will be different for the 132kW vs 155kW.

On mine, during normal cruising, pre-cat sensor voltage (sensor 1, broadband; IDE00558) bounces up and down around 1.5v and the post-cat sensor voltage (sensor 2, jump; IDE00560) bounces up and down, though with less magnitude than the pre-cat bouncing, around .6-.7v.

At idle, the pre-cat is bouncing around roughly 2.6v and the post-cat is under .25v. Expectation is at fuel cut for the post-cat to be under .2v, or something is not right. What I will see is the post-cat voltage will be flat 0v when the fuel rail pressure is doing its sawtooth pattern (IDE00589 for measured, IDE00201 for intended). If the fuel rail is held flat at spec minimum 4 MPa, the pre-cat voltage comes down under 1.5v and the post-cat voltage creeps up from 0v towards .25v. Not sure what the sawtooth vs flat thing is about, but you'll see it if you idle while logging fuel rail pressure.

At WOT, where you see the fuel rail holding around 15 MPa, spec maximum, is the pre-cat starting around 1.5v and drifting towards 1.0v, while the post-cat starts around .7v and drifts up towards .9v. Again, both always doing their bounce dance if you have high enough sample rate.

Of course, our pre-cat sensor is a wide-band lambda sensor and not an old school O2 sensor. IDE00559 is the actual measurement, lambda ratio and current flow. The voltage value presented as IDE00558 is just for convenience to the tech. The target lambda is in IDE00582 (normally 1.0).

[Primzy69]

Thanks man for taking your time to explain this stuff to me.... it lead me to something new.
We started with brake booster issue, mostly because of ruff ideling. I think i know what may be the problem... I checked camshaft adaptation and it is -5,56° (too much) plus carbon in my intake manifold.
So... lets get greasy :D