Audi A4 TDi V6 Quattro running lumpy and smoking!

[James Carlon]

My A4 seems to be smoking a lot more than it should, generally blueish/white when driving at normal speed and excessive black plumes when pulling away (more than most diesels).

I have had the turbo replaced last year as this had completely knackered. Any ideas?? I am not very mechanical so please use lay mams terms where possible!!

 

[ScottyP45]

does sound like its knackered again mate, as if the turbo is pulling its lube oil into the engine and burning it, or the head gasket has gone.

does it smoke on the over-run? i.e. when slowing from speed in gear, clutch engaged (engine braking) - if so then the valve stem oil seals may be worn, how often do you check your oil level?

Mine uses a litre (max down to min) every 6000 miles or so....

 

[aragorn]

Blueish white is oil thats being burned by the engine generally, although it can sometimes be oil thats leaking directly into the exhaust from the valve stem oil seals or the turbo oil seals. You cant be 100% sure without more investigation, where its coming from, but the turbo is a likely culprit, along with valve stem oil seals and the piston rings.

Big clouds of black is generally unburnt derv, but that might follow it being a turbo problem as if the turbo doesnt spool properly you wont have as much air in the cylinders as the ecu wants, and you'll get black smoke.

If your not mechanical then your going to have to get someone to look at it, but i'd be removing the inlet pipe to the turbo and checking the shaft for play, plus looking at the charge outlet to see if theres a lot of oil present that might suggest the turbos had it.

 

[James Carlon]

It was a brand new genuine turbo put on about September time so I really hope it isn't the turbo itself! It doesn't smoke really when idling or slowing down, more on just gentle acceleration driving around town. When I pull away hard at a junction I am now leaving a black splodge on the road!! I did experiment last year with biofuel (proper stuff not neat veg oil) but only one tank full and I have had the fuel filter changed since then just in case. Oil level is fine, doesn't use much.

 

[ScottyP45]

MAF faulty then???

 

[quattrojames]

I would say you want to get it somewhere with VAG-com and get the codes checked to see if any error codes are recorded. These are very temperamental engines (trust me!) and suffer from fuel pump problems, so it could overfueling, it could be an EGR valve problem or anything really. Get that done and go from there I reckon, even if it only eliminates those things it's worth doing.

 

[James Carlon]

How difficult is it to check/replace the EGR valve? Where is located?

 

[quattrojames]

Its top centre of the engine toward the rear, pretty easy to swap I think, costs about £70. It will show up on a code scan though so I would check first.

 

[James Carlon]

What do you reckon to these VAG.com leads and software kits you can buy on ebay? Do you think that would point out the problem accurately enough?

 

[no_idea]

I bought one, I didn't manage to get it work at the time so I bought a proper licensed one. I then realised I was trying to make it work with the wrong software version. (I think it has to be version 4?) I am not sure if these will give you the answers you need as these are 'dumb' leads and are limited in what they can do. If you pm me your address I will stick it in the post you are welcome to give it a go. It is just sitting in my garage.

 

[ScottyP45]

Ok mate, I found this article (its from BMW but refers to them and a renault diesel failure thats affecting other makes too....)

QUOTE:
What follows applies to Renault 1.5DCI engines, but may explain why the diesel turbochargers fail: The EGR valve should open to allow carbon dioxide (which acts as a cooling gas) into the combustion chambers when the engine is under load (>30% boost). This allows the combustion chamber temperature to drop and thus the temperature of the exhaust gases. If it sticks in the closed position the exhaust gas temperature will rise causing a) the turbo bearings to fail and b) engine oil into the induction system. This can cause the engine to run on its crankcase oil until it is either stalled or goes bang. Problems with EGR valves are often the cause of rough running when the valve is stuck in the open position as well. In several cases turbos have blown but the EGR valve has not been replaced. Inevitably the new turbo unit will not last long. END QUOTE

Sounds worryingly familiar eh? Easy to fix tho by checking / replacing the EGR valve. (as first suggested by quattrojames )

 

[ScottyP45]

next I found this audi article on honestjohns.co.uk:

Recalls

July 2008: TDIs with BRE engine code recalled for modified EGR valves and oil coolers to be fitted. Can cause total engine failure.

 

[JohnboyC]

James Carlon - whats the mileage on your 2.5TDi ?

 

[James Carlon]

It's done 83,500.

 

[aragorn]

TBH i've heard of many people blocking off their EGR's when they're having problems with them and never heard of turbo failure because of it...

At full throttle the EGR is closed, and thats when maximum EGT's occur. The valve is only open during part throttle to reduce the combustion temperature and reduce NOx output, at the expense of some power. When full power is demanded, the valve should close and the engine will run on 100% fresh air.

 

[ScottyP45]

what they said was that the valve jams shut, so no extra cooling at all, then the turbo seals get overheated and leak oil into the turbine, and it either cuts out or revs itself to death on its own engine oil until it goes bang or the turbo dies. I know this sounds extreme but I have seen a lorry run on its oil when the turbo oil seals went and the engine eventually blew.

Now, I cant personally see how the egr valves contribution to cooling EGT's could be enough to keep the engine below the destruction temperature of the bearing seals, unless the flippin thing is running on a ragged edge of heat tolerance which you wouldnt expect from a production car. Nevertheless, there is an audi recall for this very problem.

Just had a thought, aragorn, do you reckon it would be possible to view the EGT on vagcom and see the difference between EGR plugged and working normally? Or is the EGT not visible in vag - ive never looked for that one in the blocks list. It would be interesting to find out the difference it makes.

 

[James Carlon]

I have now had the car looked at by a diagnostics guy who found no faults! He reckons that an injector is blocked or not performing properly and needs bench testing. This sounds like an expensive job. Anyone no if any of these injector cleaner products you can get from Halfords are worth a shot?

If so, which one? Some of them are £20 a bottle, some are £8.

 

[ScottyP45]

injector magic was tested amongst others and got a top review in practical mechanics or summat a few years ago in an issue I had. Redex came out good too.

 

[aragorn]

I dont know if the TDI motor has an EGT sensor at all.

I'm not sure i'd trust what this "mechanic" has told you tbh. Anyone who plugs a computer in, and when the computer says theres nothing wrong starts coming out with "ooh well it could be..." seems to me to be a little dodgy.

You need to get the car looked at by a proper mechanic who knows their way around a diesel engine. One that can perform proper testing to see whats going on.

Lots of black smoke indicates incomplete combustion, it indicates you've injected too much diesel for the air charge present, which says either the turbo or its control gear is faulty and not producing enough air, or you have the correct amount of air but the pump is injecting too much diesel.

Blue/white can indicate either oil being burned off in the cylinders, or that the diesel isnt burning at all (ie its not firing). What does the blue/white smoke smell like? acridy oil reek or diesel?

If its diesel then the finger would point to the pump/injectors/timing. if its oil, then you'd have to look at the turbo first, then engine internals