Direct Injection - Decoke

**johnvw** · 23-02-2011,11:10 AM

Hi all,
Previously I posed a question in regard to Catch Cans, with absolutely no response, SO...

How do you address the problem of carbon buildup behind the inlet valves on direct injection engines ( without dismantling the inlet manifold).
This appears to be the major liability for direct injection and yet it receives so little if not nil attention on this Forum.
Searching the US Forums indicates that this is a BIG concern, particularly for Vw and Audi with direct injection. The use of upper cylinder lubricant appears to 'clean' and reduce the incidence of carbon buildup on the inlet valves. A number of threads and photos have been posted, regretably of earlier models, nothing specific to the A4B8 petrol engine.
I find it hard to believe the A4B8 is not subjected to this carbon problem.

Your assistance would be welcomed, particularly from the Tech`s who most be aware to this and just how to externally remove and reduce the carbon buildup.
Regards John

**theskyfox** · 23-02-2011,11:18 AM

Hi,
First of all...Im no expert in this, but it reminds me of something I read in Audi magazine recently. It suggested that the quality of fuel is a major factor to this..and they demonstrated in a V8 engine how poor quality fuel results in lots of coking/carbon build up, whereas a good fuel like Shell Optimax/BP Ultimate can help reduce this. I realise this doesn't answer your question..but I thought it might be a useful factor in helping reduce the indicidence of the problem in the first place...stick with a good premium fuel and it may help! As far as I am aware the quality of fuel in Europe tends to be of a much higher standard than that produced in some parts of the USA; giving a cleaner burn and with various additives.

-Andrew

**johnvw** · 23-02-2011,11:26 AM

Thank you Andrew,
Yes I also have read this and have no reason to doubt.
I am running a 95 octane fuel ( Caltex Australia), and using the correct 504/507 ( from memory) Audi recommended oil.
The car is relatively new and I can see small oil residue in the breather vent hose ( I expect this to continue, consequently the carbon build up ).
Regards John

**J_B204** · 23-02-2011,04:54 PM

Absolutely right, lower octane fuels don't burn as cleanly. Lived in the US for a couple of years and remember seeing fuel as low as 87RON. Part of the reason US market cars don't perform as well ad European market motors - engines can't be as highly tuned and in any case a low RON fuel will never deliver top performance or MPG, coupled with the fact that the US gallon is smaller than Imperial means comparing fuel economybetween US and European is very difficult. Whoops seem to have gone off topic sorry!

**Crasher** · 23-02-2011,05:07 PM

It puzzles me how direct injection can have a build up on the back of the inlet valve, indirect never suffered from this so maybe indirect kept the valves clean.

**theskyfox** · 23-02-2011,05:15 PM

Out of curiosity, do you think the newer generation of TDi engines may suffer from this too? The reason I think that is because as far as I'm aware both the FSI and TDi engines use the Common rail technology concept (i.e. Direct injection). As such, both the engines aren't really that far apart in engineering terms...

-Andrew

**Crasher** · 23-02-2011,06:15 PM

I think any build up on a direct injection engine, whether petrol or diesel, must be due primarily to crankcase ventilation fumes and then EGR gases, sticking to the back of a hot inlet valve.

**johnvw** · 24-02-2011,06:03 AM

Dear Crusher,
With indirect the fuel 'washes' over the inlet valve, direct injection does not hence the build up of burnt fuel/oil vapor.
I believe diesel direct injection is far worse due to the higher compression ratio ( blowby).
Regards John

**Crasher** · 24-02-2011,10:10 AM

Yeh, I kinda know that after 30 years in the trade...

My point was that due to direct injection NOT washing the back of the valve, the type of fuel used cannot be the cause for inlet valve deposits and there should be not reversion either, so any build up can only be from what comes down the ports. i.e. crankcase and EGR fumes.

**johnvw** · 24-02-2011,10:36 AM

Dear Crasher,
That`s right, but after 30 years in the trade how is this carbon build up removed, (without dismantling the inlet manifold ).
Everyone seems to suggest sucking the upper cyl. lube via a vacuum hose, I am unaware of the correct hose to use on the A4B8 ( CDN petrol ).

The IAT is mounted directly above the throttle body, I am wondering if this would be an appropriate place to temporarily insert a plastic hose and feed the lube into the inlet manifold.
It is very interesting to note lots of suggestions, but nothing specific.
Thank you for your assistance
Regards John