Possible causes of high emissions?

N

norris_309

Registered User
Joined
Mar 30, 2014
Messages
471
Reaction score
65
Points
28
Location
bristol
Hi All,

My 2004 a4 1.9tdi (avf) failed the mot the other day on a couple of things, one being the emissions. (initially I thought it was because I took that car in cold. it was still not up to 90 when I collected it after mot)

But, I've just heard back that on the re-test it failed again on the emissions & they 'tweaked' something to get it through?...
(I know I need to call the garage to see what they tweaked for more of an idea)

But while being sat in work, I'm just wondering if there is anything you guys can advise on what could cause higher emissions?

Before the retest, I put in a new air filter & ragged it around, then made sure the Mrs took it for a drive to get it to temp before taking it in.

The car had an oil change in Feb this year, fuel filter was changed last feb.

Any thoughts?
 
They'll have just revved it up for a bit to warm the CAT up.
You have to give these engines a bit of a blast regularily to clear the cr*p out of them.
I change my fuel filter at every 9k service, & would advise you do that soon.
Coolant temp sensor is a common failure & will cause the ECU to fuel incorrectly, which can cause high emissions. The only way to check what the ECU is getting from the CTS is with VCDS or diagnostics that can read the engine sensors. CTS failure doesn't always cause the EML to come on so you can't rely on fault codes to diagnose.
 
I do give the car a blast every week as the Mrs drives short distances in the cars for work. (when you say 'blast' how high revs we talking & for how long?)
Maybe I'm being a p**sy lol, I probably got 3.5k-4 in 3rd & you sometimes get a little smoke out then it seems pretty clean.

We alternate between the audi & the golf (plus her impractical mini convertible! lol) to make sure I drive the 2 dervs to get them on a run.

I normally change the oil & filter every year & the fuel/air/pollen every other, and the car does about 8k a year.
I'll take the advice on board however & change the fuel filter soon.

I've heard of people filling fuel filters with diesel cleaner before fitting?.... any input on that, I've not used anything like that before.
I nearly put some millers ecomax diesel treatment in before mot until I realised the bottle was way out of date.

CTS is interesting, I've changed the thermostat in the past as it was reading temps all over the place.

At least it's passed... I guess. but still a slight concern for me.
 
My AVF used to struggle with emissions on the MOT, but after removing the CAT it's flown through!
 
Man , it must be smoky to fail a mot smoke opacity test .

My avf is always half or less than half the 3.00 limit .
 
  • Like
Reactions: DieselJake and pauldazzle
^^ Mine has no cat or EGR or any supposed smoke helpers yet it'll easily pass the eyes of an MOT tester.

Always get a friendly MOT either way though.
 
Thats the odd thing, it's not smokey at all!? not when started up/driven normally or driven hard.
I've looked through the past MOTs and they are all well under the 3.00 limit.

The new MOT has a reading of 0.75... and only that single reading, not the usual 3 readings with the average taken.

Oh well, it's passed thats the main thing, and it seems to be running fine.
 
Indeed if at the first rev it passes clearing it's throat , no further testing is required .
 
Mrs took the car for the retest, They told her it failed again on the emissions but that they then 'tweaked' something and got it to pass??..
and that 1 reading on the mot is very low, so looks great. (until next year)
cheers for the responses
 
Don't like the sound of that , Mrs took it for retest and they 'tweaked' something !
 
  • Like
Reactions: DieselJake
Always worth changing the oil and filter with emission problems, having on average put 20+ vehicles through an MOT each year I have learnt fresh oil can go a long way to solving the problem.
 
Anyone had experience of terraclean? Basically disconnect fuel, connect this cleaning agent and run the car, it's supposed to break down all deposits and keep the engine running super smooth and lower emissions.
Saw it on WD, and thought if I ever have an old diesel I'd give it a go
 
Pops848 said:
Anyone had experience of terraclean? Basically disconnect fuel, connect this cleaning agent and run the car, it's supposed to break down all deposits and keep the engine running super smooth and lower emissions.
Saw it on WD, and thought if I ever have an old diesel I'd give it a go
Click to expand...

I'm pretty interested in this too.

If it's any good someone should set up a group terraclean or something I'd be all over that.
 
Little research and it looks as if there are about 500 service centres in the UK at the minute.
Cost wise - quote from site
We Randstad are the importers of TerraClean . We set Recommended Retail Prices. Vehicles up to 2.0L engine size £ 110.00 vehicles above 2.0L engine size £ 130.00. Larger engined vehicles including Trucks and Buses will cost more. Your local operator can give you a firm price, before you agree to the service

Find a local service agent.
https://www.terraclean.co.uk/find-a-local-agent
 
I'd look more closely at maybe a partially sticking egr valve , after all it's those dam devices why they are so smokey and later decided a dpf was needed .

Another flawed device to fix another flawed device...
 
You must log in or register to reply here.

Similar threads

JamieOS
My 1.8T Failed MOT/NCT on emissions and also has high fuel consumption.
Replies
5
Views
3K
pauldazzle
pauldazzle
ei2gfb
high pitched whinning from rear of car
Replies
4
Views
763
ei2gfb
ei2gfb
a4sline190
Mot Emissions
Replies
1
Views
725
A4Andy
A4Andy
A
Thinking of selling,valuation help if possible?
Replies
24
Views
1K
BahnStormer77
BahnStormer77
Pabs
Emissions Control Light
Replies
6
Views
760
paulsb
paulsb
Top
Back