2007 2.7 tdi aut. - humming, resonating noise on low rpms when cold

[cozmo]

Weather has gotten quite cold here in Norway during the last month, and during this period our 07 A6 2.7 TDi has developed (or maybe it's always been like that - got the car this summer in warm weather) kind of a humming or vibrating noise - or just very noisy engine rattle.

This is almost only noticeable when started in cold weather (like +5 Celsius), AND typically most prominent when going slow in 2nd or 3rd gear and going off the accelerator. Like when you've gotten up to speed and slowly take the foot of the accelerator and the rpms decreases. Seems to be happening most on rpms between 1200-1500. Like a loud engine humming, or some kind of resonating noise...Like somehting is vibrating...Hard do describe - as always with car noises

I am not able to reproduce this noise with car in neutral and slowly pressing and/or releasing the accelerator. It is ONLY when car is in gear and moving.

It is almost not noticeable when engine has reached operating temperature.

Any immediate thoughts? Intake manifolds? Gearbox?

I've done ALL work myself on all my previous vehicles (all Saabs and Citroens), but looking under the engine cover on the Audi I was blown away on how little space there is to get around things. Also - I've never worked on a diesel engine before - so I feel kind of helpless

[niall campbell]

Firstly you simply lift off the engine cover and all parts like diesel filter, oil filter are quite easily accessible .

Run car with cover off and see if you still have a rattle, there are 3 or 4 points on the cover that have rubber gromets and they maybe are perished

Failing that start car and look and listen for any pipes disconnected.

All diesels have a " diesel knock " when cold. As the engine warms up, this will decrease.

When was the last service for the engine oil & what oil is in it ?

I change my diesel filter every 20,000 miles as they don't have drains for water, this will make your diesel freeze .

[cozmo]

Thanks for your reply.
I've tried to listen for various pipes disconnected etc, but as I wrote - the sound only occurs when car is in motion and in gear. That makes it a lot harder - because as soon as you are moving - wind noise in your ear as you lean out of the window effectively disrupts most noises from the engine compartment.

I know diesels have a knock when cold. This is is with no doubt somehting different.

Car was last serviced about a 1.5 years ago (long life service) by the previous owner. On the printout it only service "long life oil, 50700B" ...

[niall campbell]

Can you jack the car up on axle stands, switch engine on and engage a gear ?

Is the noise in the gearbox or at the wheel ? Nothing to do with brakes , as in the brake disc shield isn't touching the brake disc ?

Is there a noise if you turn the steering wheel over to the left or right ?

How many miles has your car done ?

Have you changed the transmission oil/ gearbox oil ?

[cozmo]

While I do have had cars on four axle stands before, I'm not that comfortable with such a setup that I feel comfortable running the car while it's up there. Maybe I'm just paranoid...

I'm unfortunately not able to determine exactly where the noise is coming from. However, I'm very confident that it is not coming from the wheel areas, neither is it related to the servo-pump or steering in general. I've replaced several servo-pumps and steering racks on other cars, and this is definately not something like that.

It feels exhaust or turbo related. I suddenly remembered I had something similar on my Saab 9-5 couple of years ago - it made this "humming" noise when engine was pushed on lov revs and high gear. That turned out to be the turbo bypass valve - or often refered to as the "hooter"-valve on petrol turbo cars.

Do these Audi diesel engines have such a valve? I realize I have to read up on turbo-diesel engines..

[markaz]

Can you scan with VCDS? Could it be the engine mount solenoid valve being faulty?

[cozmo]

I'll do a VCDS scan as soon as I have the time.

Engine mount solenoid valve ? Never heard of such a thing. What does it do?

[markaz]

Copied from another site:

the way the mounts work is that there is a fluid chamber with a plastic body in the middle of it, with small channel cut through it. this allows fluid from the top chamber, through the plastic body, to the bottom chamber. the bottom chamber is rubber lined and can deform under pressure. there is also an airway vented to atmosphere, with a rubber membrane separating the fluid from the atmosphere. a solenoid valve, controlled by the motronic, can open or close the airway.

below 1100 rpm (i.e idle), the engine vibrations are not enough to force fluid from the top chamber, through the passageway to the bottom chamber. the airway is open (solenoid valve open). the rubber membrane creates a soft cushion which absorbs the high frequency vibrations.

above 1100 rpm the soleniod valve is closed which blocks the airway and so "hardens" the mount (the fluid has nowhere to go). thus the mount is effectively solid.

the high frequency vibrations at speed are absorbed by the membrane (as in the idle case), while the more damaging low frequency vibrations cause the fluid to force itself through the chamber in the plastic body to the lower chamber, forcing the (lower) rubber chamber to distort - effectively absorbing the vibrations.

[MarkTM]

Tiptronic tranny fluid/filter change according to zf should be done at 50k miles thereafter. Dirty or low fluid will not show on a VCDS scan.

[cozmo]

Got around doing a VCDS scan today.
What gets me a little worried is the glow plug faults. But they are dated half a year back...??

Copied the modules with faults from the log :

Thursday,05,November,2015,11:59:04:62939
<snip>


00-Steering Angle Sensor -- Status: OK 0000
01-Engine -- Status: Malfunction 0010
02-Auto Trans -- Status: OK 0000
03-ABS Brakes -- Status: OK 0000
05-Acc/Start Auth. -- Status: Malfunction 0010
06-Seat Mem. Pass -- Status: OK 0000
07-Control Head -- Status: OK 0000
08-Auto HVAC -- Status: OK 0000
09-Cent. Elect. -- Status: OK 0000
0E-Media Player 1 -- Status: OK 0000
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
18-Aux. Heat -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
34-Level Control -- Status: OK 0000
36-Seat Mem. Drvr -- Status: OK 0000
37-Navigation -- Status: OK 0000
42-Door Elect, Driver -- Status: OK 0000
46-Central Conv. -- Status: Malfunction 0010
47-Sound System -- Status: OK 0000
4F-Centr. Electr. II -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
53-Parking Brake -- Status: OK 0000
55-Xenon Range -- Status: OK 0000
56-Radio -- Status: OK 0000
57-TV Tuner -- Status: OK 0000
61-Battery Regul. -- Status: Malfunction 0010
62-Door, Rear Left -- Status: Malfunction 0010
65-Tire Pressure -- Status: OK 0000
67-Voice Control -- Status: OK 0000
69-Trailer -- Status: OK 0000
6D-Trunk Elect. -- Status: OK 0000
72-Door, Rear Right -- Status: OK 0000
76-Park Assist -- Status: OK 0000
77-Telephone -- Status: OK 0000

-------------------------------------------------------------------------------
Address 01: Engine Labels: Redir Fail!
Part No SW: 4F7 910 401 D HW: 4F0 907 401 C
Component: 2.7L V6TDI G000AG 0020
Revision: --H05--- Serial number:
Coding: 0011372
Shop #: WSC 02334 758 00200
VCID: 24470A1BE72E243ED0B-8071


4 Faults Found:
005658 - Glowplug for Cylinder 1 (Q10)
P161A - 001 - Open Circuit
Freeze Frame:
Fault Status: 01110001
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 145226 km
Time Indication: 0
Date: 2015.04.29
Time: 17:47:05


Freeze Frame:
RPM: 840 /min
Torque: 128.7 Nm
Speed: 0.0 km/h
Duty Cycle: 1.0 %
Voltage: 13.68 V
Duty Cycle: 21.3 %
Temperature: 15.3°C


005659 - Glowplug for Cylinder 2 (Q11)
P161B - 001 - Open Circuit
Freeze Frame:
Fault Status: 01110001
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 145226 km
Time Indication: 0
Date: 2015.04.29
Time: 17:47:05


Freeze Frame:
RPM: 840 /min
Torque: 128.7 Nm
Speed: 0.0 km/h
Duty Cycle: 1.0 %
Voltage: 13.68 V
Duty Cycle: 21.3 %
Temperature: 15.3°C


005660 - Glowplug for Cylinder 3 (Q12)
P161C - 001 - Open Circuit
Freeze Frame:
Fault Status: 01110001
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 145226 km
Time Indication: 0
Date: 2015.04.29
Time: 17:47:05


Freeze Frame:
RPM: 840 /min
Torque: 128.7 Nm
Speed: 0.0 km/h
Duty Cycle: 1.0 %
Voltage: 13.68 V
Duty Cycle: 21.3 %
Temperature: 15.3°C


005661 - Glowplug for Cylinder 4 (Q13)
P161D - 001 - Open Circuit
Freeze Frame:
Fault Status: 01110001
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 145226 km
Time Indication: 0
Date: 2015.04.29
Time: 17:47:05


Freeze Frame:
RPM: 840 /min
Torque: 128.7 Nm
Speed: 0.0 km/h
Duty Cycle: 1.0 %
Voltage: 13.68 V
Duty Cycle: 21.3 %
Temperature: 15.3°C


Readiness: 0 0 0 0 0


-------------------------------------------------------------------------------


-------------------------------------------------------------------------------
Address 05: Acc/Start Auth. Labels: 4F0-910-852.clb
Part No SW: 4F0 910 852 HW: 4F0 905 852 B
Component: FBSAUDIC6 ELV H31 0230
Revision: 09010701 Serial number: 10601500906415
Coding: 0000135
Shop #: WSC 02323 758 00200
VCID: E3C5C90722A0E306691-80B6


Subsystem 1 - Part No: 4F0 910 131 G
Component: FBSAUDIC6 EZS H45 0080


Subsystem 2 - Part No: 4F0 910 335
Component: FBSAUDIC6 KSG H27 0080


Subsystem 3 - Part No: 4F0 910 220 K
Component: FBSAUDIC6 IDG H01 0060


1 Fault Found:
00956 - Key 2
002 - Lower Limit Exceeded - Intermittent
Freeze Frame:
Fault Status: 00110010
Fault Priority: 3
Fault Frequency: 52
Reset counter: 176
Mileage: 146790 km
Time Indication: 0
Date: 2015.08.13
Time: 08:17:46




-------------------------------------------------------------------------------


-------------------------------------------------------------------------------
Address 46: Central Conv. Labels: 4F0-910-289.lbl
Part No SW: 4F0 910 289 K HW: 4F0 907 289 K
Component: Komfortgeraet H26 0210
Revision: 02100026 Serial number: 01072545550000
Coding: 3547889
Shop #: WSC 02335 758 00200
VCID: 326BFC43ADDABA8E527-8067


Subsystem 1 - Part No: 1K0 951 605 C
Component: LIN BACKUP HORN H03 1301


Subsystem 2 - Part No: 4F0 910 177
Component: Innenraumueberw.H01 0020


1 Fault Found:
01699 - Motor for Central Locking; Hatch/Trunk (V53)
009 - Open or Short to Ground - Intermittent
Freeze Frame:
Fault Status: 00101001
Fault Priority: 3
Fault Frequency: 8
Reset counter: 171
Mileage: 147730 km
Time Indication: 0
Date: 2015.09.19
Time: 12:22:14




-------------------------------------------------------------------------------


-------------------------------------------------------------------------------
Address 61: Battery Regul. Labels: 4F0-910-181.lbl
Part No SW: 4F0 910 181 E HW: 4F0 915 181 A
Component: J0644 BEM H12 0590
Revision: 00000000 Serial number: 00000000156264
Shop #: WSC 00493 128 52362
VCID: 23450907E2202306A91-8076


Subsystem 1 - Part No: 4F0 915 105 E
Component: von VA0 57100770SK
Coding: 34463039313531303545205641303537313030373730534B
Shop #: WSC 00000 384 00290


5 Faults Found:
02272 - Quiescent Current Stage 1
000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 7
Fault Frequency: 8
Reset counter: 255
Mileage: 145287 km
Time Indication: 0
Date: 2015.05.21
Time: 14:44:36


02273 - Quiescent Current Stage 2
000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 7
Fault Frequency: 6
Reset counter: 255
Mileage: 145287 km
Time Indication: 0
Date: 2015.05.21
Time: 14:51:03


02276 - Quiescent Current Stage 5
000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 7
Fault Frequency: 3
Reset counter: 255
Mileage: 145287 km
Time Indication: 0
Date: 2015.05.21
Time: 14:51:13


02274 - Quiescent Current Stage 3
000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 7
Fault Frequency: 3
Reset counter: 255
Mileage: 145287 km
Time Indication: 0
Date: 2015.05.21
Time: 14:51:23


02277 - Quiescent Current Stage 6
000 - - - Intermittent
Freeze Frame:
Fault Status: 00100000
Fault Priority: 7
Fault Frequency: 2
Reset counter: 255
Mileage: 145287 km
Time Indication: 0
Date: 2015.05.21
Time: 14:51:33




-------------------------------------------------------------------------------
Address 62: Door, Rear Left Labels: 4F0-910-795.lbl
Part No SW: 4F0 910 795 E HW: 4F0 959 795 E
Component: TSG HL H21 0210
Coding: 0017450
Shop #: WSC 02327 758 00200
VCID: 2E53E833B9E29E6E36F-807B


1 Fault Found:
02110 - Window Regulator Switch
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 3
Fault Frequency: 2
Reset counter: 185
Mileage: 148073 km
Time Indication: 0
Date: 2015.09.30
Time: 11:46:05




-------------------------------------------------------------------------------