Where’s This Bit From? . . . . Tonight’s Quiz

[mmi]

The EGR injects inert gas into cylinders to reduce oxygen concentration of the fuel/air mixture, which slows combustion, which leads to a reduction in the peak
combustion temperature, which reduces nitrogen oxide emissions. Lambda sensor provides long term feedback for EGR to keep oxygen level as "low" as possible.

NOx sensor is purely on exhaust aftertreatment side - provides feedback to AdBlue system to clean the leftover NOx emissions.

 

[n10n]

@DXX
Some help - hopefully...

View attachment 118719

I have no idea what I’m talking about but noticed the rpm and rail pressure dipping, could these really be affected by EGR flap alone? I’m thinking something more mechanical like compressor or something in the clutch. Or maybe VGT flexing as commanded charge pressure peaks?

Edit: switchable water pump solenoid could make such noise and affect rpm as pressure changes. By looking at scope graphs it’s hard to tell which change comes first and which are reactions.

 

[mmi]

True chicken-egg problem! My thought has been it's all EGR driven, which causes significant/sudden change in air flow, at the same time ECU tries to maintain steady RPM which in turn causes the rest - e.g. fuel pressure and charge pressure jump around.

The data was logged almost 5 years ago - everything brand new then.

Anyways, something similar was mentioned here

Noise at 1350rpm

Hi guys i need help. wierd noise coming from my 2016 T6 140HK TDI DSG, non adblue version I think it’s the last t5 engine. The sound appears time to time, mostly when I drive and the engine is warm, but maybe 1/50 rides the sound also appears in neutral (also warm, never cold) today it did so...

www.t6forum.com

 

[n10n]

True chicken-egg problem! My thought has been it's all EGR driven, which causes significant/sudden change in air flow, at the same time ECU tries to maintain steady RPM which in turn causes the rest - e.g. fuel pressure and charge pressure jump around.

The data was logged almost 5 years ago - everything brand new then.

Anyways, something similar was mentioned here

Noise at 1350rpm

Hi guys i need help. wierd noise coming from my 2016 T6 140HK TDI DSG, non adblue version I think it’s the last t5 engine. The sound appears time to time, mostly when I drive and the engine is warm, but maybe 1/50 rides the sound also appears in neutral (also warm, never cold) today it did so...

www.t6forum.com

Indeed. Yours sounds much more like sharpish clunk rather than a woosh in the other threads. Also idling vs slightly increased rpm. But could there really be two separate mystery sounds with similar frequency?

I don’t particularily wait for detecting similar in my van although I must admit this is VERY intriguing and it would be really interesting to see if internal CAN or larger set of advanced measuring values could fork out some insights.

 

[mmi]

Spoiler: Cheat sheet 1

G18

Spoiler: Cheat sheet 2

5Q0898047

Spoiler: Cheat sheet 3

Webasto doesn't work - Caravelle T6

Do you have any idea why it stops by itself? The cause is stored in fault codes (of controller 18-Aux. Heat)

www.t6forum.com

 

[Dellmassive]

i loved this quiz. . . . we should start doing it again.

 

[MagicOli]

Well, not exactly a bit, rather T6 diesel behaviour - every now and then.

T6. Engine hot. Starts when vehicle has reached standstill. Engine on tick-over - 830 RPM. Stop/start doesn't shut off the engine.

Sound clip attached - a "hiccup" regularly every 1.5 seconds. Can last up to two minutes. Recording made outside. Best heard on right side of vehicle (standing by right front wheel). Can be heard in cabin, too.
View attachment 118644
View attachment 118631

@mmi Did anyone work out what this sound is caused by? Our T6 at 22k has the same noise in exactly the same conditions as you described. Now at 27k and still the same. Drives fine. What is that component in post #65?

 

[mmi]

@mmi Did anyone work out what this sound is caused by?

It's caused by the sudden stop (slow down) of the air flow in the air filter box and air intake ducting. Those parts are made of such a thin plastic so they expand a by sudden flow stop inside thus making the thudding sound. The engine measures the blockage of EGR cooler by alternating exhaust flow between EGR cooler and direct flow to exhaust. So better the cooler, more change in air flow, and thus more sound. Perfectly normal operation for the engine.

The noise can be reproduced even controlled way - by running engine's build-in EGR test - link below

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

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 -...

www.t6forum.com

What is that component in post #65?

It's a temperature sensor in the auxialiary coolant heater/parking heater. Just click open up the cheat sheets in the "spoilers" and eventually a link to part's diagram.

 

[MagicOli]

It's caused by the sudden stop (slow down) of the air flow in the air filter box and air intake ducting. Those parts are made of such a thin plastic so they expand a by sudden flow stop inside thus making the thudding sound. The engine measures the blockage of EGR cooler by alternating exhaust flow between EGR cooler and direct flow to exhaust. So better the cooler, more change in air flow, and thus more sound. Perfectly normal operation for the engine.

The noise can be reproduced even controlled way - by running engine's build-in EGR test - link below

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

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 -...

www.t6forum.com

It's a temperature sensor in the auxialiary coolant heater/parking heater. Just click open up the cheat sheets in the "spoilers" and eventually a link to part's diagram.

That’s an impressive level of knowledge, thank you for explaining it. So, do all T6 diesel engines make this sound when up to temp and idling?

 

[mmi]

So, do all T6 diesel engines make this sound when up to temp and idling?

That's what I believe - at least the EU6 engines (with AdBlue). However, they do it only every once in a while - not happening everyday.