Another game of what's this noise?

[temporarysecretary]

I occasionally hear this noise coming from the engine bay. It is very intermittent but I have only heard it at idle with a warm engine.

Van is T6 BiTDI DSG 199.

The noise is a dull knocking sound that comes from the engine bay but can be heard in the cabin if you switch the radio off. It sounds like it's coming from the back of the bay somewhere.

The van drives great. Nice smooth power delivery not using any fluids. Serviced regularly and oil analysis on every oil change.

 

[mmi]

Post in thread 'Where’s This Bit From? . . . . Tonight’s Quiz'

6 Jun 2021

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 T6_CXEB_Hiccup_20181213.mp3

• mmi

• 

Post in thread 'Where’s This Bit From? . . . . Tonight’s Quiz'

7 Jun 2021

I give up on this one. 830RPM = 13.83 R/sec / 2 for 720 deg for injection at tick over = 6.91 secs. Not divisible by 1.5

Thank you very much for the interest Actually I don't have definite answer so explanations, opinions, ideas... all are welcome.

My thought about the phenomena is that the engine is doing a kind of EGR calibration. As the EGR cooler gradually gets clogged, EGR needs to be adjusted accordingly to maintain optimal combustion conditions.

Below a zoomed out version of the recording above - but just two parameters (EGR closure vs. air flow)

So basically...

• mmi

• 

 

[temporarysecretary]

Post in thread 'Where’s This Bit From? . . . . Tonight’s Quiz'

6 Jun 2021

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 T6_CXEB_Hiccup_20181213.mp3

• mmi

• 

Post in thread 'Where’s This Bit From? . . . . Tonight’s Quiz'

7 Jun 2021

I give up on this one. 830RPM = 13.83 R/sec / 2 for 720 deg for injection at tick over = 6.91 secs. Not divisible by 1.5

Thank you very much for the interest Actually I don't have definite answer so explanations, opinions, ideas... all are welcome.

My thought about the phenomena is that the engine is doing a kind of EGR calibration. As the EGR cooler gradually gets clogged, EGR needs to be adjusted accordingly to maintain optimal combustion conditions.

Below a zoomed out version of the recording above - but just two parameters (EGR closure vs. air flow)

So basically...

• mmi

• 

Interesting.

Thank you for highlighting that one. I have searched all over the forum for a similar clip and not found one before.

It's sounds like the same noise other than when mine does it the frequency is higher. Rather than a single hiccup every 1.5 seconds mine tends to be a larger hiccup then multiple smaller ones.