Heads up Carbon on Porky DI engines

[Andyuk911]

I have spoken about this before.,

This is just to provide a heads up on what WILL happen to the New Direct Injections Porsche engines,

ie 997 Gen 2 etc

http://www.planetporsche.net/cayman-boxster-chat/3...

My advise is regular oil changes and use of the Wynns products

http://www.wynns.be/news.aspx?l=EN&isectionid=...

[Two Stallions]

So glad I have the 997.1 model.

[baz1985]

So DFI can now be lambasted as 'Directly F8cked-up Injection'.

[Andyuk911]

In a word yes.... it has great benefits for power and emissions ... but within a few thousand miles kills itself.

More cars will move to Direct Injection and over time the cleaners will get better

[Two Stallions]

I had a Mitsubishi GDI (petrol) engine back in 2003. It went back to Mitsubishi twice to have the valves de-coked! It was a massive problem, confirmed by the service department. Glad to get shot of that car.

[AndrewKillington]

Andyuk911 said:

In a word yes.... it has great benefits for power and emissions ... but within a few thousand miles kills itself.

Andy
What are the syptoms? loss of power? smoke?
Kills itself in a few thousand miles

[Two Stallions]

My Mitsubishi gradually started to run rough and stalled on a couple of occasions. De-coked and ran OK for about 20K miles!

Edited by Two Stallions on Monday 12th October 12:22

[Andyuk911]

AndrewKillington said:

Andyuk911 said:

In a word yes.... it has great benefits for power and emissions ... but within a few thousand miles kills itself.

Andy
What are the syptoms? loss of power? smoke?
Kills itself in a few thousand miles

Sorry, my post was a bit OTT ...

From known tests of Audi RS4s it takes about 2-4k miles for the carbon to build.

When I sold my RS4 at 30k miles, it was running absolutely fine .... but as somepoint if will need a decoke.

The point of the post was to show it happens to Porsche, hence the original link above.

The bottom line, over time performance will reduce ...

[Andyuk911]

Two Stallions said:

My Mitsubishi gradually started to run rough and stalled on a couple of occasions. De-coked and ran OK for about 20K miles!

Edited by Two Stallions on Monday 12th October 12:22

Did they clean it for free? ..... I bet not .... I think they should have done!

[Two Stallions]

The first one was done under warranty, the second one was a "goodwill gesture"..... 'kin goodwill gesture, it's a design fault and they try to make it sound like they're doing you a favour!

[SFO]

this is quite staggering ...

engineer out the IMS, introduce lots of coke.

madness

[Ian_UK1]

Two Stallions said:

The first one was done under warranty, the second one was a "goodwill gesture"..... 'kin goodwill gesture, it's a design fault and they try to make it sound like they're doing you a favour!

To be honest it's not a design fault. As you're aware, the coking-up of the back of the valves is caused by oil particles from the crankcase rebreather and oil seepage down the inlet valve guides. This is normal in any internal combustion engine and is just a characteristic of burning fuel/air in an enclosed, oily environment. It was just a lucky thing that manifold fuel injection washed the backs of the valves clean on every inlet stroke of the engine. It also kept them much cooler too due to evaporation of the fuel as it hit the valve - this also tended to keep any oil from sticking and carbonising. DFI just goes back to what used to happen before manifold fuel injection and also happens in all diesels - no direct fuel spray to wash the inlet valves clean.

It WILL, however kill the performance of the engine over several thousand miles as the deposits build up. Firsly the valves don't flow any air at small openings and secondly the overall effective diameter of the inlet tracts is made smaller. This has the additional effect of changing the shape of the inlet tracts to the detriment of flow and also adds a very large and turbulent boundary layer. Thirdly, any swirl action on the inlet charge is compromised and designed-in stratification of the charge in the chamber will suffer. It will be interesting to dyno these engines at, say, 5000miles and then again at 20,000. Wonder just how much they'll lose?

Back to the 'good old days' of decoking your engine every 25000 miles or so I'm afraid.....

Ian

Edited by Ian_UK1 on Monday 12th October 16:02

[Ian_UK1]

Andyuk911 said:

My advise is regular oil changes and use of the Wynns products

http://www.wynns.be/news.aspx?l=EN&isectionid=...

I'm not sure that the Wynns products will do any good - the deposits on the backs of the valves are so hard, they virtually have to be machined off. I've heard of workshops soaking the valves, once removed from the engine, for 24-hours or more in chemical cleaners (not unlike Wynns) to no avail. So unfortunately, I don't think a few milliseconds exposure to the spray as it passes the valves whilst the engine is operating will do anything at all.

[shoestring7]

Two Stallions said:

I had a Mitsubishi GDI (petrol) engine back in 2003. It went back to Mitsubishi twice to have the valves de-coked! It was a massive problem, confirmed by the service department. Glad to get shot of that car.

Yup, I had months of running problems with an Fsi engined Audi A2, the eventual cure was a decoke.

SS7

[Andyuk911]

Ian_UK1 said:

Andyuk911 said:

My advise is regular oil changes and use of the Wynns products

http://www.wynns.be/news.aspx?l=EN&isectionid=...

I'm not sure that the Wynns products will do any good - the deposits on the backs of the valves are so hard, they virtually have to be machined off. I've heard of workshops soaking the valves, once removed from the engine, for 24-hours or more in chemical cleaners (not unlike Wynns) to no avail. So unfortunately, I don't think a few milliseconds exposure to the spray as it passes the valves whilst the engine is operating will do anything at all.

Ian,

I do agree with you in one breath.

Wynns(and others) know the problem, they did produce a doc showing it helped.

The only real way is to a before and after ..... but I don't know anybody who could do this.

I wonder if Porsche will cough up to decoke an in warranty new 997 gen2.

I know of one RS4, that had a damaged to an injector and another with non sealing valve.

I think most manufactures will be forced to DI, purely to meet emissions ..

[D900SP]

This has been a problem for many years: The 928 had similar problems and the repair was to remove the intake manifold and walnut-shell blast the intake ports.

I have seen 996 engines with similar issues, to the extent that the engine ran rough due ta excessive leakdown caused by carbon on the valve seats.

Part of the issue (IMHO) is that most engines are desgined for constant high-rpm operation and what actually happens is low speed town driving with long periods of idling and the occaisonal "spirited" drive.
We currently have a 14K mile 2006 997 cab that runs rough due to carbon issues, it's whole life has been low-speed town driving for very short distances....

As we can run the number of operating hours the engine has onthe system tester, dividing that number by 30, usually gives the actual miles driven as on the odometer, most cars are around the average speed of 30 mph.....

Edited by D900SP on Monday 12th October 18:34

[Andyuk911]

D9000sp,

to clarify, even if you use super unleaded with all the cleaning additives, this does not stop the carbon as NO fuel passes the valves.

For a 996, this problem does not happen, as the fuel is injected into the intake track and 'washes' the valves. No coke will build up with Super unleaded.

There is a sound case to say a 997.1 will have better long term performance over a 997.2


ps

If you have a carbon issue, switch to Super unleaded(97/98/99)(it has cleaning additives), DON'T run 95 in your car.

Edited by Andyuk911 on Monday 12th October 20:14

pps

I have just noticed you are in the US ... get your customer to use high quality gas .... why don't you 'Seafoam' the car .. that will fix it ....then reset the ECU

Edited by Andyuk911 on Monday 12th October 20:50

[SunDiver]

There's a picture below in the link of what MRC found on the new-model RS4 - also a direct injection engine.

http://www.mrctuning.com/index.php?option=com_cont...

"The valve stems were coated in a carbon layer and gummed up with an oily residue further restricting air flow. This is a common appearance in FSI cars due to the lack of fuel passing through the intake manifold and cleaning any deposits that build up over time..."

[D900SP]

Andyuk911 said:

D9000sp,

to clarify, even if you use super unleaded with all the cleaning additives, this does not stop the carbon as NO fuel passes the valves.

For a 996, this problem does not happen, as the fuel is injected into the intake track and 'washes' the valves. No coke will build up with Super unleaded.

There is a sound case to say a 997.1 will have better long term performance over a 997.2


ps

If you have a carbon issue, switch to Super unleaded(97/98/99)(it has cleaning additives), DON'T run 95 in your car.

Edited by Andyuk911 on Monday 12th October 20:14

pps

I have just noticed you are in the US ... get your customer to use high quality gas .... why don't you 'Seafoam' the car .. that will fix it ....then reset the ECU

Edited by Andyuk911 on Monday 12th October 20:50

We strongy advise our customers to only use Chevron, Shell or Texaco "premium" grade fuel. The preference is Chevron.

The last 996 we repaired with poor running had so much carbon debris the valves were being held open, with the exhaust removed we could feel and see the leakage when using a leakdown tester. The intakes were the same.

Recently rebuilt a 928S4 engine that would not start due to the valves being held open by a mixture of oil and carbon with also the piston rings stuck in the lands. Again, an everyday short trip car.

Drive a town use only Cayenne TT and compare to a "driven as it should be" TT and note the performance, even making allowances for the transmission map.

The 997.1 with the running problem actually "diesels' when turning off. Not much can be done about this apart from repairing the engine. This is not an unknown issue.

We have tried various additives, they do help, but do not "cure".

I also think that the oil-change intervals are way too far apart, I recommend, at the minimum, once a year depending on how the vehicle is driven. We use only Mobil-1 on water cooled current Porsche models.

[Andyuk911]

You are talking about a DIFFERENT issue to me.

To be clear, if you run a DI engine on the super duper fuel it WILL carbon up.

If you run a 996 etc 'normal' injection on super duper fuel it will NOT carbon up.

What you are speaking about is LOW GRADE GAS in the USA, this is NOT relevant to this thread.