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D3 - Engine Bay Everything under the bonnet

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  #1  
Old 12th May 2022, 06:43 PM
rory_pamphilon rory_pamphilon is offline
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Default Odd pump/grumbling noise from engine bay when coming to a stop

Hi,


Have had this symptom for a while, no real issues with the car other than this but im curious what may be causing it.

When coming to a stop, can be a gentle or harsh stop, doesnt really matter, i can hear something that sounds a bit like a pump, splutter and then stop. A bit like an engine stalling if it were manual and you stamped on the brakes, except its not the engine obviously. Quite difficult to describe, its not particuarlly loud, coming from front/possibly left hand side of the engine bay. It definately sounds like something that is struggling to keep running as car slows to a stop and the minute the wheels stop this thing chugs and dies.

Things I have checked/changed...

Air con, had this regassed the other day, no issues reported. Old gas was still fine and pump seems fine.
Car serviced recently, oil/filters changed etc, didnt fix the problem.
Tryed running aircon in econ mode for a while, this possibly reduced it a little but i might just have been imagining it.
Very slight leak on radiator, top it up every month or so.

Could it be the secondary air injection pump?


Thanks
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  #2  
Old 13th May 2022, 10:43 AM
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steamship steamship is offline
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Not sure if this applies to your car, but some D3s had an electric vacuum pump in the braking system. If yours has it, it might be a vacuum leak from that causing the issue, especially if you notice it when braking to a standstill.

Might be worthwhile updating your signature line to include the specifics of the car, for future reference.
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Old 19th May 2022, 05:34 PM
rory_pamphilon rory_pamphilon is offline
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Hi,

Sorry not sure whats up with my signature, i thought i had one. will update asap.

My A8 is a 3.0Tdi QS 2007.

How can i tell if it has the extra vacum pump that you mention? Is it something you can see if you lift the bonnet?


Thanks
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Old 20th May 2022, 08:51 AM
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steamship steamship is offline
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Quote:
Originally Posted by rory_pamphilon View Post
My A8 is a 3.0Tdi QS 2007.
Just checked and the electric vacuum pump in the braking system only applies to the petrol engines (BBJ, ASN, BVJ and BSM).

Now this or may not be relevant, but might be worth checking for a perished pipe. The 3.0tdi also has a vacuum system on the EGR, but no idea how it operates. The attached image might help.
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
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  #5  
Old 30th May 2022, 09:08 AM
rory_pamphilon rory_pamphilon is offline
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Thanks,

I will have a look into this. Ive noticed zero issues really apart from the odd noise so not in a major hurry, its curiosity more than anything.

Will feedback if/when i know more.

Cheers
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  #6  
Old 31st May 2022, 01:05 PM
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This will likely be your air suspension compressor. It turns off when the car comes to a stop. It also pumps out a jet of air through the outlet to purge the air dryer.

As the compressor ages and itís piston ring gets worn, it will become noisier.

Mike
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