q2bruiser

So I scheduled my first oil change with the dealer. First one is free here so please no smack about doing it myself.

I talked to the service adviser about DFI engines and the possibility of intake valve crud buildup due to ERG (I know there is no valve). The service adviser says there is no service recommended and kept going on about the 997.2 not having an EGR valve ... as though not having a valve somehow negates the process of EGR. All he would say is "those German engineers figured it out". Maybe he is correct but after seeing all the crud on Audi engine intake valves it makes me wonder.

Have any of you talked to your dealers about this?

James

ADias

I doubt that you need any intake cleaning at this stage. At 40/50k miles perhaps a Top Engine Cleaner treatment.

Macster

EGR (exhaust gas recirculation) takes place. It is a very good way to lower combustion temperature and reduce NOx emissions.

In the DFI engines it is accomplished by variable valve timing and lift to allow some exhaust gases to mix with the incoming air to lower the combustion efficiency of the next combustion cycle.

The problem is exhaust gases are forced to flow not out the exhaust valves but the other direction to some extent.

This puts hot exhaust gases in contact with relatively cool intake valves. Upon contact and cooldown the exhaust gases will deposit solids. On the face deposits will be burned away or removed by the gasoline and its chamber cleaning additives.

However, some exhaust gases will flow even further up the intake system and contact the back side (the upstream side) of the intake valves. The hot exhaust gases will then deposit material on these cooler valve surfaces. These deposits are not removed by gas injected in the chamber cause gas doesn't get up there. Build up can occur.

At some point build up will effect the very critical air flow into the chamber and combustion efficiency which depends upon fairly precise swirling of the enrushing air will fall. This can increase the deposit forming content of the exhaust gases which exacrebates the problem.

Another problem is the build up might get bad enough to start to flake off and the engine can ingest some of the deposits. They are relatively soft but a piece can get stuck in between a valve and its seat momentarily.

The deposits also cause the the valve to gain weight. The valve springs have to cope with a "heavier" valve and this can have bad consequences if the valve deposit weight gets too great.

Run a good brand of gasoline. Buy from a busy station to get fresh gas. Try to avoid real low RPM operation. This is harder to do with DFI engine connected to PDK cause fuel economy requires the PDK shift up very quickly to keep RPMs low and cut fuel consumption.

On a related note try to avoid short trips that fail to get the engine up to temperature and the oil hot.

Use a good grade of oil and don't run it too long. If you run the oil too long it gets contaminated and becomes more fluid. This can result in oil getting past the rings and adding to the deposit forming compounds in the exhaust gases.

Contaminated oil will be more likely to aerate. This will help to increase the oil vapor content of the crankcase air. The oil vapor separator system may be overwhelmed and as a result route crankcase fumes to intake system for burning with a higher load of oil and other crankcase air contaminates. All of these of course can only increase the deposit forming load of the exhaust gases.

Sincerely,

Macster.

ADias

Excellent analysis. Don't you think that periodic Top Engine Cleaner applications would be a good thing and clean up the intake tract?

Macster

Best if possible to avoid getting engine in a condition any top end cleaning needs to be done.

Granted some owners/drivers of these DFI engine'd car will not be able to take all but only some and maybe none (can't be bothered, don't think about it, don't care, etc.) of the steps I believe will help prevent valve deposits. And I do not know for sure, but even if one followed the guidelines eventually deposits could accumulate.

Even if a periodic top end engine cleaning necessary I'd want to do it as infrequently as possible. There's cost, which probably won't be cheap.

But my info is -- second-hand -- that the cleaning process will involve running engine -- at idle? or something higher? -- and feeding it a cleaning compound in the form of a vapor or perhaps a light mist. The amount of time this treatment takes could be minutes to perhaps a large fraction of an hour.
Maybe more if engine's intake valves particularly heavily desposited.

In the meantime this cleaner is removing the valve deposits it can also be working to wash away some of the oil from the cylinder walls. At idle any reduction in the quality of the cylinder wall/piston/piston ring interface will be less harmful, but not without some risk of harm.

The cleaner could also compromise the lubrication of the lower end -- the end nearest the valve heads -- valve stems/guides.

Of course the cleaner will have to be selected that removes valve deposits and yet doesn't harm the O2 sensors or the converters.

Then after the cleaning I'm almost sure and oil/filter service will be required cause some cleaner that goes into the chambers will not completely exhaust out the exhaust ports but end up in the oil which will dilute the oil.

I'm not saying the (possible) cure is worse than the disease but the cure -- top end engine cleaning -- is not without its own set of issues.

Sincerely,

Macster.

q2bruiser

Thanks Macster. I agree with your synopsis which is why I am curious about the cleaning. I am fortunate that mine is not a daily driver and I always get the temps up. I will be changing the oil every 6 months as well.

Hopefully she stays clean up top but I don't see how the intake valves will not incur some buildup.

JKH

8haggis

If I can add just a bit more information on EGR...

Engines which have EGR valves have what is called external EGR. This is the routing of the exhaust gas from the exhaust manifold to the intake manifold by piping and its flow is controlle d to the engine by an EGR valve.

In this system, the exhaust gas interfaces with all of the induction system from the throttle body to the cylinder. (Intake manifold, fuel injectors, intake valves, etc.)

The engines without EGR valves have what is called internal EGR. This is the ingestion of exhaust gas into the combustion chamber and is achieved and controlled by varying the valve timing. This is sometimes referred to as VCT, VVT, iVVT, Valve Phasing, and the such. In the 4-cycle combustion process, simply put, you would do the following:
Open intake valve, pull down piston sucking air from intake, close intake valve, move piston up to compress gases, ignite, move piston down to generate work, open exhaust valve, push piston up to expel exhaust gas, close exhaust valve, repeat.

To achieve internal EGR, you change the timing of the overlap of the exhaust and intake valves to alter the above sequence of events. (I will cut into the above cycle at the point of work generation.):
move piston down to generate work, open exhaust valve, push piston up to expel exhaust gas, move piston down to suck in exhaust gas from exhaust manifold, close exhaust valve, open intake valve, continue to move piston down and suck air from intake, close intake valve, move piston up to compress, ignite, repeat.

This is a bit simplified as there is actually some valve overlap which means that both valves are open at the same time for both engines, but that would make the explanation less clear.

A lot of durability and performance testing was performed to determine the necessary maintainence schedule recommended by the OEM, but over-maint of the vehicle is likely only harmful to your pocket book.

q2bruiser

Sounds like the service writer at my dealer is right.

JKH

Macster

Hopefully not the same ones that "figured" out the IMS of the older style engine.

That said, I don't think the new DFI engines will load up their intake valves if given reasonable servicing and use. And maybe not even if given unreasonable servicing and use.

I almost bought a new Porsche with a DFI engine. Just so happens I found a used 996 Turbo first. But my next Porsche will almost certainly have a DFI engine and might even have a PDK transmission.

The new Porsche I considered had DFI engine but 6-speed manual transmission. I'm actually a bit more leery of the PDK than I am of the new DFI engine. I do not necessarily think the PDK bad or premature but I'm more concerned how it works in the every day driving I engage in. I didn't take a test drive of a PDK car but will have to have one before I commit.

But this is a few years away. In the meantime I get to sit back and see how the new DFI engines and PDK transmissions hold up and what if any issues they may have.

Sincerely,

Macster.

RPMert

FWIW, How about this stuff? Even though Porsche says, "No additives," it can't hurt, IMO. Unless new direct injection is weirdly different.

nyca

A fuel additive isn't the solution here, this cleaning on a DFI involves injecting the solution directly into the intake rail - which on a DFI engine, has no fuel in it, just air and the recirculated exhaust gas which has oil in suspension.

I've been reading that when Mercedes brings DFI to the US, there is going to be a refillable cannister on the car that holds such a solution.

Has anyone with a 997.2 had their oil tested after an oil change, to see if it has fuel in it? The audi's are doing this too, fuel mixed into the oil - apparently from the high pressures atop the cylinder forcing it down in the crankcase - another reason to change oil in such an engine more frequently then the manufacturers spec.