Audi v8 carbon build up?

[blueb10]

Hi;
I think most people are aware that the Audi v8 can suffer from carbon build up. Is there any effective preventative solution to this, such as fuel treatments (Wynns, redex, etc)?
Thanks.

[OPOGTS]

Other than the occasional 'Italian Tune Up' i've not read about anything else that works.

MRC seem to be the widely recognized experts to fix any problems >>> https://mrctuning.com/site/rs4-b7-4-2-v8-fsi/

And the RS246 forums have a wealth of info >>> https://forum.rs246.com/viewtopic.php?f=35&t=9...

RS246 said:

Carbon deposits within the inlet tract which is generally accepted as being caused by valve overlap, a feature of the FSI system. Symptoms can be exhaust smoke, lack of power and in extreme cases, misfiring. Initially it was thought that it was due to excessive oil vapours from the crankcase ventilation system but oil catch cans retro-fitted to some cars have remained largely dry. While many cars will be fouled internally with no problems, only very few actually exhibit any symptoms and these tend to have performed frequent short journeys in urban areas or steady motorway cruising with little use of high revs. If cleaning is required this can be performed by a specialist for around £600 but how long it will remain clean is unknown. Impossible to check before buying really.

[Dr G]

Drive it and enjoy it.

In the event that it becomes an issue have a proper carbon clean carried out by a specialist. There is a tool approved by Audi and a specific grade of walnut blasting media. The fuel system treatments and injected liquid/gas are snake oil.

[blueb10]

Thanks.
Mine is the RS5 and i do occasionally like to use the performance, the v8 sounds great at 8000 rpm.
I just thought that maybe as it is a direct injection engine that the better fuel additives might help reduce the carbon build up.

[FMOB]

blueb10 said:

Thanks.
Mine is the RS5 and i do occasionally like to use the performance, the v8 sounds great at 8000 rpm.
I just thought that maybe as it is a direct injection engine that the better fuel additives might help reduce the carbon build up.

My understanding is the direct injection of fuel into the cylinder rather than using the inlet manifold means the oily residue from the engine breathers in the inlet manifold doesn't get 'cleaned' by air/fuel mixture and eventually turns into carbon deposits by the hot engine.

As the fuel doesn't go into the inlet manifold where the issue occurs you see why fuel additives have no effect on this problem.

[rottenegg]

Nope, no prevention. Not even if you dump the PCV to atmosphere. Exhaust reversion will still carbon up the valves regardless.

Italian tune ups is a thing that's 20 years out of date. Doesn't work on Diesels (clogs the DPF even more) and doesn't work on DI petrol either as it just bakes the carbon onto the valves even more, plus extra blow by PCV oil dumping onto them. Carbon burns off at 400 deg C, so it's not practical to keep the combustion temps at that level for extended periods.

It's worse on n'asp engines as they don't have turbos to force the air in around the intake obstructions, so the airflow restriction is a thing unfortunately and does rob the 4.2 of power if it gets bad enough.

Maybe try switching to 5W40 (if the standard oil is 5W30) and check/replace the PCV, which might slow down the fouling a bit.

Petrol DI is another missold 'green' benefit along with diesel. Absolutely minimal mpg benefit, in spite of only injecting as the piston nears TDC. The only benefit is higher compression ratio because of the cooling effect of spraying directly into the combustion chamber.

It's no coincidence that a lot of high performance VAG engines now have port injection as well as direct.