Best way to prevent cokeing up/carbon issues?

[CycleSi]

Hope to be collecting my RS4 this week with only 21k.

Assuming it is not already coked up, then what is the best way to prevent it from happening? I know they need to be revved regularly but what else would help?

Thanks,
CycleSi

[Rick_RS4]

It'll be coked just not as bad. Mine was after 4k.

Do a search been covered a few times. Quire recently actually

[CycleSi]

Most of the posts seem to cover how to remove the carbon as opposed to preventing it in the first place.

[adsgreen]

Hope to be collecting my RS4 this week with only 21k.

Assuming it is not already coked up, then what is the best way to prevent it from happening? I know they need to be revved regularly but what else would help?

Thanks,
CycleSi

Nothing massive
- don't overfill the oil
- don't do short journeys
- Do use full throttle and RPM where possible (when oil up to temp and appropriate / safe do so).
- try to get some heat into the engine once in a while (get the oil nice and hot)

Even then it won't go away.

You *could* use some Direct Injection cleaner - a good place could be the vacuum line just by the manifold actuator flaps as this goes straight into the intake manifold and won't hurt the fragile MAF sensor. Not sure what it'd do to the one way valve though... Some people use a football pump adapter and poke it in where the MAF goes.

And yes - it will have coke. I'd wager possibly quite bad depending on how the previous owner used it over their 3k miles / year driving.

[bam_bam]

Ahhhh, the C word.
I love it.

[JohnFC]

I bought my first RS 4 (a 2006 cabrio) a year ago at 56,000 miles. It has been dyno tested and diagnosed at 8% down on the expected 414 bhp due to coking. Since then (about 8 months ago but only 4,000 miles on) I have used Momentum 99 fuel from Tesco, Audi Fuel Additive about once a month (probably not doing anything but makes you feel good!) and given it regular bursts to the red line. I am easily fooled but I believe further coke can at least be minimised; primarily the higher grade fuel clearly maximises the bhp but also assists to slow down carbon build up.

[coldo]

Agree the best way is to just use it as intended.

That said, I've got a 65k car, never been carbon cleaned to my knowledge, yet the 0-60 and the 3000rpm-8000rpm tests were conducted and the car performed as a standard car in good order is expected to. Also went up against cars of similar power (E92 M3, 380bhp Impreza, Evo X FQ360) and again matched up as you'd hope. I appreciate you can't disregard the low dyno results some cars make but I'm inclined to say that the power loss from 'coking up' isn't as bad as people make out.

Incidentally the people who noise up this known issue are often the ones who've never owned a B7 RS4, like my mate with a ford puma, for example... he insists my car is only making 330bhp as they all 'coke up' by 50k!

[PetrolDave]

Most of the posts seem to cover how to remove the carbon as opposed to preventing it in the first place.

That's because you can't - carbon build-up to some extent is inevitable in any 100% direct injection petrol engine. There's no fuel vapour in the inlet manifold to wash off any EGR/blow-back effect so carbon build-up WILL happen.

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Interesting reading on the latest GDI engines... looks like a combination of things has reduced it. The main one ironically is changing the valve / injector timing along with the fuel spray pattern so make sure fuel doesn't contact the intake valve. Apparently this is a major contributor... I wonder if early GDI designs were trying to use the fuel spray to clean the valves inside the cylinder and actually made things worse.
Who knows... the sad point is that on a B7 there's nothing you can do.
Accept it, don't worry about it and move on.

[GAZ-MAN]

I use tesco momentum petrol and not going to lie it gets driven hard pretty much everyday obviously once heaten up properly, that's what these cars are made for and why they rev like they to do get driven hard "my opinion anyways "

[Brooner]

i think you have to factor in a carbon clean as part of your maintenance if your keeping the car long term i had mine first done at about 30k then 45k just to see how much build up there was it was worse than i thought iw would be after 15k but i was going to do this every 15k if i kept the car

[lexos]

Hi,
Sorry for my poor english, but you can really avoid having carbon back...

Of course you can avoid having it again.. I confirmed that. I cleaned up mine at 85000km, now I have got 130'000km, no carbon , nothing (after reopening).

You have to :

- clean it first (of course)
- remove the not working part from audi (the oil separator with triple cyclones)
- close the entry (by removing the oil separator you will get a hole there).
- install a catch can (or at least a pipe)

The main problem is the oil separator, which is not working as it must. Oil are going back to the admission where it was supposed to have only air...
So if you don't remove that part after cleaning, you will get the same issue after some kilometers.

Be aware that you cannot just remove it and close all the remaining pipes...This motor needs to breathe (in both directions). So you have to permit the oil vapor to leave the engine and some air to come back if needed.

regards.

[adsgreen]

not always the case. Other people have fitted catch cans in addition to the OEM PCV and not reported any benefit.

[TonyHayers]

The oil separator works like that by design, by the way...

Blow-by gas volume is dependent on engine load and RPM. The fine oil (“oil spray”) is separated by means of a cyclone separator. Cyclone separators have a high separation efficiency over only a small volumetric range. For that reason, one, two, or three cyclones of the fine oil separator operate in parallel, depending on the gas-flow rate.

The cyclones are released by the control piston. The displacement of the control piston against its spring force is dependent on the gas-flow rate. Piston ring flutter at very high engine RPMs and low engine load can result in a very high gas-flow rate.

The crankcase internal pressure is set by the two-stage pressure control valve. The bypass valve, together with the control piston, ensures that the cyclones operate at the optimum operating point (if the volumetric flow rate is too high or too low, it will impair the functioning of the cyclones).

When the bypass valve opens, a fraction of the blow-by gas flows to the engine untreated, but the remainder is optimally treated by the cyclones.

[barryrs]

I do wonder just how effective the oil separator is though.

"Blow-by gas volume is dependent on engine load and RPM.

The cyclone oil separators have a high separation efficiency over only a limited volumetric range. For that reason, one, two, or all three cyclones operating in parallel will be needed depending on blow-by volume.

Internal crankcase pressure is regulated by the two-stage pressure control valve. The by-pass valve, together with the control piston, ensure that the cyclones work at the optimum operating point. If the volumetric flow rate is too high or too low, it will impair cyclone operation.

When engine load and RPM are high, blow-by gas flow volume is high. Blow-by gas pressure against the control piston works against the spring pressure and opens passages to more cyclones.

Separated oil is collected in an oil reservoir beneath the cyclones. It cannot drain out of the reservoir until the oil drain valve is opened. The oil drain valve is closed as long as the pressure in the crankcase is higher than in the oil separator. The valve opens automatically due to gravity
only at very low engine RPM or when the engine is not running because the pressures are at equilibrium.

When the engine is running at very low load but at a very high RPM, the piston rings can begin to flutter. The blowby gas pressure is very high and the fine oil separator is unable to operate at its peak efficiency. At this point, the by-pass valve opens and a fraction of the blow-by gas flows to the intake manifold untreated."