Technical advice required RE: inlet manifold carbon deposits

[matthew.lewis2]

Apologies for the length of this post.

Right then, I dropped my car off this morning for Audi to investigate my 'cold morning hesitancy'. I explained I wanted the inlet manifold removed to check for carbon build-up as I suspected this was the cause (I know the hesitancy is a 'feature' of the RS4!!)

Anyway, the master tech was quite defensive, and was reluctant to remove the manifold, capitulating in the end. He pointed out repeatedly that he knew how this engine worked. I tried to re-assure him that I was not questioning his professional judgement, but, I too had some degree of understanding of how this engine worked, and felt that there was an inherent problem.

Can I ask the forum for technical reasons to (hopefully) rebut the following hypothesis proposed by the master tech: -

1. Carbon build-up is due to our poor petrol quality in Dubai. Despite me pointing out that fuel does not pass directly through the inlet manifold as it is an FSi engine (I pointed out that this was part of the cause for the deposits not being washed away), he suggested that the inlet valves were open for a period of time to introduce turbulence whilst fuel is in the cylinder (not sure whether he meant during or after injectors are open) and hence fuel can enter the inlet manifold.

2. He seemed to think carbon build-up is normal. And questioned who would determine that X amount of carbon build-up was excessive, necessitating a claim under warranty for the cleaning. I did point out that had the cyclonic separator been operating as intended, there would not be so much oil vapour in the inlet manifold causing the carbon build-up.

The works being undertaken on my car are as follows: -
1. Check TPI software update ECU available
2. Remove intake manifold and check for carbon build-up
3. Perform compression test
4. Perform injector cleaning
5. Replace leaking DRC suspension (passenger side)
6. Replace engine carbon trims
7. Check rattling from grille next to overhead light

[silverRS4]

The hesitancy upon cold starts is typically an injector problem. The a failed injector(s) may be leaking, allowing the residual fuel pressure in the fuel rail to enter the combustion chamber when the engine is 'off'. The accumulation of fuel in that cylinder causes a misfire upon cold start. The misfire and rough running only lasts 20-30 seconds and then the engine appears to run normal. The misfires can be numerous and a CEL or MIL light is normally shown. This problem can be detected with injector leak-down tests and the faulty injector(s) can be identified. Usually, all eight injectors are replaced. There is no hard evidence showing that the carbon buildup that occurs in every RS4 FSI engine is directly related to injector problems - they appear to be two separate issues.

There may be some fuel that momentarily enters the intake port after fuel spray before the valves close, but its hardly enough to have a cleaning effect on the buildup. That is a poor excuse at best. And yes, carbon buildup is normal on FSI engines; however the buildup rate is such that it can take 10 hours of manual cleaning and walnut shell blasting to remove buildup on a 4.2 FSI with 5,000 miles. Buildup several millimeters thick has been noted ON EVERY SINGLE 4.2FSI engine that's had the manifold removed, whether they have 5,000 miles or 25,000 miles. Fuel quality is not the issue. Driving habit is not the issue. The root issue is inherent with the car. Some Audi dealers are beginning to recognize this, some are not. Regardless of what Audi thinks now, the buildup will at some point affect the performance of the car and have a negative affect on the catalysts. The high amount of oil vapor in the crankcase ventilation system is not removed effectively with the current cyclonic separators, which has a negative affect on ignition timing - again reducing performance. It is a widespread problem that is for sure. I hope your dealer takes a close look at it without relying solely on assumptions.

[ghoonk]

Would it be easier to replace the valves?

[silverRS4]

Would it be easier to replace the valves?

That would require removal of the engine and disassembly of the cylinders heads - huge job. In addition to the cleaning work, the intake manifold removal (for access to the valves) and reinstallation takes a dealership about 4 hours. The walnut blasting is very effective and is probably going to be the method of choice for all FSI valve cleaning. I hear Audi is buying up land in Brazil and southern France. Walnut tree orchards perhaps?

[sonny]

Do they clean both banks or just the inlet banks of Valves?

Interesting read, hope they get it sorted either way, let us know how you get on

[silverRS4]

Sonny, are you referring to the exhaust valves? If so, due to the much higher operating temperature of the exhaust valves, and the fact that oil vapor has been combusted or deposited in the inlet stream, and the direction of flow past the exhaust valves is in the opposite direction when compared to flow past the intake valves, one would expect to find very little carbon on them (who knows with a FSI engine, though). Access to the exhaust valves would require removal of the engine, so lets hope its not an issue. My opinion concerning the catalysts relies on the assumption that any carbon deposits that dislodge from the intake valves will pass through the engine during combustion and redeposit on the catalyst cells. Will they stay there or will they cook/vaporize? Hard to say. Maybe the carbon won't really be an issue on the exhaust side of things. And as for Audi planting walnut trees, I am only kidding.

[yorkie]

Would Brazil nuts be too coarse?

[Gazzer68]

Would Brazil nuts be too coarse?

What the shell or the nut?

[aidanjaye]

The use the shells.

[sonny]

Sonny, are you referring to the exhaust valves? If so, due to the much higher operating temperature of the exhaust valves, and the fact that oil vapor has been combusted or deposited in the inlet stream, and the direction of flow past the exhaust valves is in the opposite direction when compared to flow past the intake valves, one would expect to find very little carbon on them (who knows with a FSI engine, though). Access to the exhaust valves would require removal of the engine, so lets hope its not an issue. My opinion concerning the catalysts relies on the assumption that any carbon deposits that dislodge from the intake valves will pass through the engine during combustion and redeposit on the catalyst cells. Will they stay there or will they cook/vaporize? Hard to say. Maybe the carbon won't really be an issue on the exhaust side of things. And as for Audi planting walnut trees, I am only kidding.

OK makes sense, touch wood.

[yorkie]

Chocolate Brazils wouldn't be much use then!

[aidanjaye]

Chocolate Brazils wouldn't be much use then!

Not really but probably wouldn't make any more mess than whats on the inside of FSI engines....

[SR71]

matthew,

You must obviously be familiar with pippyrips car on this forum?

Check various threads that pertain to it, but, suffice to say, his car has always been run on Shell Optimax and/or Tesco 99.

This the best fuel one can get in the UK and have a look at the inside of his car. Optimax has been specifically recommended to various owners by a certain oil guru because of the cleaning properties of the additives but even they cannot cope with the volume of s**t being fired into the inlet side of this FSI V8.

Print out a few pictures and show them to your mechanic to refute the notion that this issue is dependent on fuel quality.

Even better, tell him the latest shots are the result of only 2000 miles motoring, and ask him again if he thinks the cyclones are working?