What is it that makes a 100k diesel sound like a tractor?

[jammy_basturd]

Got an Audi A3, that has done nearly 100, 000 miles, and typically of a diesel it sounds like a bag of spanners. It's been fully serviced on time all it's life and been taken well care of.

What makes it sound like a bag of spanners, is there anyway to get it sounding nearly as smooth as it did when it rolled off the production line?

[Fetchez la vache]

My saab diseasal has always sounded like a bag of spanners...

[EDLT]

VAG's TDI engines always sound a bit agricultural. How old is it?

[Zad]

A new injector pump and a set of injectors?

Price them up and then realise why they don't get replaced just because they sound a bit rough.

[jammy_basturd]

Ahhh, so it's the injection system that is the cause of all/most of the noise?!

It's a 2001 car.

[Patrick Bateman]

I would imagine it sounded much the same brand new...

[Petrolhead_Rich]

Not just VAG, my volvo s40 (ford engine) was quiet at 30k, but now with 130k it sounds like a pixy is hammering the piston down with a hammer!

I did manage to get it to improve with a good oil flush and change, but it's still not as good as it was!

[anonymous-user]

"diesel" combustion noise is incredibly sensitive to the rate of pressure rise in the burn cycle, and as the engine runs with excess air at all times, this rate of pressure rise is completely dependant on the injected fuel quanitity and it's burn rate. Modern common rail diesels do as many as 5 "pre" injections to try to smooth the "Noise" (that is 5 seperate tiny little squirts of fuel before the main big injection). As the injector nozzles wear, the exact timming and dispersion of these fuel "clouds" changes, and the combustion noise tends to increase. The EMS system will try to "adapt" it's individual cylinder fuel quantity and timing to minimise noise (which is why you find "knock" sensors now on diesels!!)


If you want to waste a fun** 10 mins, start a modern diesel engine from cold, leave it idling, and see if you can spot the moment the ems swaps to "pre" injection mode (for emissions and fuel economy reasons, the initially cold engine with just be running with "main" injections only)

BTW, if you really want to hear what it sounds like, take the oil filler cap off at idle and have a listen down the hole, it's HORRIBLE to listen too!! (and shows yoy how much the acoustic covers etc actually do)

• no express guarentee can be given to ensure that this is in fact "fun" for all or any parties, individuals or other sentient life forms attempting this sort of thing, and a strict policy of zero refund in the case of dissapointment will be maintained ;-)

Edited by anonymous-user on Sunday 21st November 12:01

[GTRmad]

EGR valve

[uuf361]

VAG diesels are not the quietest even when new in my experience.....

[redgriff500]

Can sound MUCH louder if a cambelt change is bodged and pump timing it out.

[Dave J]

ford engines have problems with the harmonic damper going, this makes the engine rough and nosiy

[masermartin]

uuf361 said:

VAG diesels are not the quietest even when new in my experience.....

In my experience too - my Bora is noisier than my old man's Focus, although granted there's 25k more miles on it too.

[GingerWizard]

thrust bearing on the gear box is a noisy rattle and quite common on diesels to become loose...

[Mr2Mike]

The PD engines sounded like a bag of spanners straight from the showroom. If it's worse than a new one it could be that a timing belt change hasn't been done very well and the pump timing is out.

[anonymous-user]

My neighbour has a brand new A3 tdi, 1.9 I think, it sounds hellishly rough and noisy, noisier than any of its competitors, I assumed VAG diesels all sounded like that, irrespective of mileage?

[Merlot]

The XUD in my Dturbo sounds like a knackered Transit.

Still, they all sound like that and for a daily driver I'm happy for the trade in exchange for 50mpg!

[paoloh]

I have an Astra with a 1.7 CDTi engine in it. Injectors went and I had a 2nd set fitted and the engine is considerably more tappety and it sort of hangs around after taking your foot off the accelerator but what is weird, is the noise goes the higher up the rev range you go.

Does this sound like the new set of injectors are worn?

[Wycombe83]

Merlot said:

The XUD in my Dturbo sounds like a knackered Transit.

Still, they all sound like that and for a daily driver I'm happy for the trade in exchange for 50mpg!

Yep clatter my XUD goes on a cold morning, not to mention the blue smoke it belches out once it fires. Amazingly you don't get the smoke whilst it warms up.