204 DSG intermittent momentary power loss

[mmi]

oh, ok, im a complete newb to logging and what not, ill have another go today.
do I need to drive the van for each log to be saved?

1) blockmap - engine not running - just turn ignition on and create the blockmap file (cold engine is just fine)
2) Turbo actuator test - engine idling (cold engine is just fine)
3) Turbo changeover valve test - engine idling (cold engine is just fine)
4) EGR test 1st - engine idling (cold engine is just fine)
5) EGR test 2nd - hot engine idling - thus a bit of driving to warm up the exhaust

 

[mmi]

log files from earlier

Thank you very much for the log files - and especially having markers in the files - helps to pinpoint and confirm the moments of the issues.

Some preliminary thoughts... about the last logged session (of total of three in the recording).

Large scale view in time of markers whereabouts​

A downselected period for closer view - from 760 to 775 seconds​

Well, probably the most illuminating period because of

• high vehicle speed = high engine load
• only few gear changes
• also "things" happen at slower rate thus easier to understand

General conditions - speed, engine revs​

No noticeable glitches in engine speed signal - not even by zooming in.

Turbo actuators​

Obviously at about 764 seconds the pedal was floored, the gear was stepped down to 4th at 764 seconds, and stepped up into 5th at 768.5 seconds.

Turbo vane actuator (blue) and turbine changeover actuator (grey) reach and stay at their "full blast" positions.
Turbo wastegate (red) regulates charge pressure until...

Charge pressures as seen by the ECU​

I guess the pressure drop seen at 767 and 770.5 seconds drive the ECU to start to close the wastegate (squared red in picture one above).

Air mass flow & engine torque​

Air mass flow is in sync with charge pressure - quite naturally. And of course the recorded/calculated engine torque follows.


QUESTION - does this happen also on gear 7?

In the log the 6th gear was used and marked at 830 seconds (below).

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It has been remapped, though I don't think it was a very good one.

My guess is that the turbo just can't handle the excessive air flow and the airflow in turbine vanes simply suddenly "slips" ???

Unfortunately I don't have reference values at the same conditions (4th gear full blast at and above 3800 RPM). Only thing similar by speed I found was only 130 grams/second of air flow - just barely half - but that's on 7th gear so also number of cylinder fill-ups is about half of what would have been on 4th gear.

Of course a culprit could also be a misbehaving manifold pressure sensor (which are known to get clogged). Or misbehaving wastegate actuator or valve.

 

[Cog Head]

Thank you so much for your input & analysis

It happens in all gears if I pull away wile towing the caravan, I booted it in the logging to try to simulate that.
I’ll get the block file and other tests you requested today.

I’d like to get to a point where we can isolate a certain part, or few suspect parts that I need to look into, rather than shooting in the dark at random parts and getting nowhere with it.

We aren’t going away to Europe with it this year, but I’m building a bit of a fear of the motorway hills around Santander in Spain, anyone who’s been there will know them.
The thought of attempting to scale those hills with this high demand / load power dropping out, isn’t very appealing at all.

 

[Cog Head]

turbo and recirculation test

 

[Cog Head]

blackcap from earlier too, the engine wasn't completely cold, it was left parked after towing said caravan home after the weekend.

 

[mmi]

turbo and recirculation test

Thank you.

Turbo actuator test - sweeps a few times from min to max - OK as expected based on the logged journey.



Turbine changeover valve test - sweeps a few times from min to max - OK as expected based on the logged journey.



Also both pressure sensors read same value as seen earlier thus no suspects there either.



Also the wastegate can also be tested using VCDS but the recorded data already shows that it operates correctly.
Just fullfilled/edited the procedure into the posting

Post in thread '[T6_measured] 01-Engine - Built-in tests for turbocharger'

13 Oct 2024

01-Engine - Basic Settings​

IDE07136-Test of wastegate actuator (only Bi-Turbo)​

HOW-TO​

Engine running​

VCDS > Select > Engine > Basic Settings > IDE07136-Test of wastegate actuator​

Select "Measuring Values"​

Pick up the following data items for monitoring:

IDE00021 Engine RPM​

IDE00347 Air mass: actual value:​

IDE07736 Turbocharg.2 compress.outlet: press.sensor 1 bank 1: raw value​

IDE07738 Charge air cooler inlet: pressure sensor 1 bank 1: raw value​

IDE07744 Particle filter: air...​

• mmi

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I’d like to get to a point where we can isolate a certain part, or few suspect parts that I need to look into, rather than shooting in the dark at random parts and getting nowhere with it.

I think the issue is that the requested 3.5 bar charge pressure is simply too much asked. Stock CXEB does at maximum only 3.1 bar.

Still interested to see results of the EGR test - to evaluate DPF condition - as the blockmap data a kind of suggests some degree of blockage there.

4) EGR test 1st - engine idling (cold engine is just fine)
5) EGR test 2nd - hot engine idling - thus a bit of driving to warm up the exhaust

Thread '[T6_measured] 01-Engine - Built-in test for EGR'

23 Apr 2023

So it seems - inevitable P0401.

Well, visited a VW garage to be tested - the van had accumulated 30 events in ECU's memory since July 2021 (since 20 months now). Eventually managed turn on the emission light at event number 31 - thus had a priviledge to have EGR flow tested. The result - pending - the ODIS went to an unending loop without a concluding result.

Meanwhile, I think I have reproduced the EGR flow test using VCDS. However, I don't have any reference value to estimate the degree of EGR cooler blockage. Neither did ODIS tell the reference value (should have told but the computer...

• mmi
• egr p040100 t6_measured
• Replies: 83
• Forum: Engine, Gearbox, Exhaust, Drivetrain

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[Cog Head]

Once again, thank you!

I’ll try to get the EGR & watergate actuator tests done this evening.

Does the van need to be driven or will a period of ticking over be ok to get the exhaust hot enough?

 

[mmi]

Does the van need to be driven or will a period of ticking over be ok to get the exhaust hot enough?

Whatever is convenient for you - we'll be in the right ballpark anyway - as the actual temperatures are recorded



S3 is DPF input
S4 is DPF output

 

[Cog Head]

I’ll do this in the morning, I just realised the van is parked rot next to the neighbours house, I don’t think they’d appreciate me running tests at 22:21

 

[Cog Head]

egr test - cold
waste gate actuator test

 

[Cog Head]

hot erg test log is attached

 

[mmi]

waste gate actuator test

I believe the below is just ECU output to sweep the wastegate actuator from it's minimum to maximum thus not it's actual position.

I believe there actually is no electrical feedback from the actuator itself. Can't find anything suitable in measurement values. Also the workshop manual wastegate adjustment procedure doesn't give anything electrical reference - just a mechanical setting.

– Apply a vacuum of 390 ± 10 mbar to vacuum unit.
– Move lever arm -1- in direction of -arrow- and hold in closed position.
– Screw nut -2- in direction of vacuum unit until it comes into contact with lever arm -1-.

Thus the wastegate adjustment feedback comes from pressure sensors to relieve excessive pressure.



Anyways, we can indirectly verify that the wastegate actually does move by monitoring e.g. the pressures after the turbos. The sensors plotted are actual values from the sensors (below)


I would conclude that the wastegate works correctly.

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Just to complement the above - also was verified the other two actuators do not affect analysis as they are stationary during wastegate sweeping. They are swept into their "rest" position and held there during the test (below). They do have position sensors - read as voltage below.

 

[Cog Head]

while I’m in the van I’m running a manual DPF regen
This is the screenshot before

 

[Cog Head]

Part way through with a few more datapoints

There seems to be a lot of soot and ash mass in there, do you think that could be causing engine back pressure and the boost to spike and stall the turbo vanes momentarily?

 

[mmi]

while I’m in the van I’m running a manual DPF regen

Can you run the EGR test again - after finished DPF regeneration - thus to see pressures of a "clean" DPF?

 

[Cog Head]

after regents EGR test

 

[Cog Head]

Completed DPF regen
The soot amount has dropped to -2.80, not entirely sure why a negative number is show there

 

[mmi]

hot erg test log is attached

Engine RPM​

EGR valve position​

• 0 = no exhaust recirculation,
• negative value = exhaust recirculation through the EGR cooler
• positive value = EGR cooler bypassed - not seen above, but somewhat explained in [T6_measured] Winter specialities

Airflow at intake while EGR valve is sweeped​

An estimate of EGR cooler performance based on air flow ratios between EGR min/max positions​

Based on reference data in [T6_measured] 01-Engine - Built-in test for EGR - very good.

Differential pressure across the DPF​

Fairly high pressures were observed - in comparison with data in [T6_measured] 01-Engine - Built-in test for EGR
Of course fairly high soot content at the time of test contributes to higher values (as the pressures will be lower immediately after DPF regeration)

Differential pressure across the DPF - Double scaled illustration​

Temperatures along the exhaust pipe​

just to verify the conditions are comparable with other measurements as the DPF differential pressure strongly correlates with DPF temperature

 

[Cog Head]

Thanks again for your time!

So as I understand… I may be wrong… EGR is good, DPF, is good, turbo actuators are all good…

So we’re looking at the remap as the possible problem as it’s asking for too much boost?

 

[mmi]

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There seems to be a lot of soot and ash mass in there, do you think that could be causing engine back pressure and the boost to spike and stall the turbo vanes momentarily?

That's a possibility - at least a contributing factor - especially if the power loss didn't happen earlier.


The ash mass is a calculalated value for DPF lifetime expectancy - it's assumed that at 110 g it's all finished.

However, I'm more concerned about relationship between soot calculated and soot "measured".

Normally DPF regeneration is triggered solely on calculated value which sweeps from 5..6 to 24 grams (on your engine).
As the "measured" is most likely based on differential pressure across DPF, it normally is much less than the calculated.
However, whenever the "measured" reaches the calculated it will take the control of the DPF regeneration.

In the blockmap data we see that DPF has reached the state that soot measured can take the controls. E.g. on April 3rd the DPF regeneration will be triggered by soot measured (16 grams calculated vs. already 23.08 grams "measured" - regen will be triggered at 24 grams)



My statement would be that the DPF needs to be replaced (or cleaned) in any case fairly soon to avoid too frequent DPF regens (which actually are already happening every now and then (16 vs. 23 grams).

It's probably the accumulated ash which is the potential problem - the ash won't burn away being a residual of burned soot and oil additives.

Thanks again for your time!

So as I understand… I may be wrong… EGR is good, DPF, is good, turbo actuators are all good…

So we’re looking at the remap as the possible problem as it’s asking for too much boost?

EGR + cooler = ok
DPF is about to reach critical state - quite possibly contributing to the power loss issue, too.
Turbo actuators = ok
Fuel pressure = ok (though not mentioned here)

A thought about DPF flushing on T6​

Post in thread 'DPF Regen Frequency / Issues / Force discussion.'

9 Jul 2023

Both 2019 vans so I guess so.

Thanks - good to know. I have had concerns about DPF cleaning because on T6 NOx SCR catalytic converter (the NOx trap) is integral part of the DPF - just not to flush also the catalyst coating (likely "only" copper zeolite).

VW SSP 564, p.28.

SSP 564 - The T6 2.0L TDi

VW Self Study Programme, Document 564 - The 2.0 litre TDI Engine In The T6 The introduction of modern, particularly efficient Euro-6 engines represents a central feature of the new T6. All units are equipped with Blue Motion Technology as...

www.t6forum.com

The coating material is mentioned in the VW Self Study Programmes below - e.g. available here

VW SSP 424 Exhaust Gas Aftertreatment System Selective Catalytic Reduction,​

VW SSP 540 SCR Exhaust Gas Treatment (Passat...​

• mmi

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