2009 997.2 Carrera Cab Black residue on exhaust tips
 

Hey Porsche Friends
Is it normal to have black residue on the stainless steel exhaust tips?
And if so How and what can clean it off?

I think that is pretty standard on the DFI engines.

There have been many comments on the tips. Seems like many have done the ceramic coating on them. May want to look into the threads?

I've used P21S Total Auto Wash and paper towels. Don't want to spend too much effort because they just get dirty again. I've thought about the ceramic coating thing, but if you let them get dirty enough they look like they are ceramic coated. *shrug*

Any metal polish with a fine grit in it will work just fine.
Wash them first to get most of the crud off,then use the polish.

Simple Green and even wheel cleaner and a brush will clean most of the soot off. Then you can further clean them with metal polish and refinish the brushed look with fine sand paper.

Now after you dot his every 2-4 weeks chasing clean exhaust tips and get tired of that you can unbolt them and sand them down and spray paint them with black hi-temp exhaust paint

Not a DFI exclusive. I see plenty of blackened tips in port injection engines. This is due to smog-control rich running reqs.

As others stated - no big deal to clean, easier if done regularly. Steel pipes are easel polished with any .

Actually for smog/emissions compliance these engines run on the lean side, at around 14:1 air:fuel ratio.

It is at this (or nearly this -- I think the actual air ratio is a fraction higher) that the converters are most efficient. Their efficiency drops quite a bit if the mixture gets much richer (or leaner). The window of ideal is very narrow.

The only time these engines operate richer (ignoring when started from cold) is when the driver via his right foot makes a big enough torque demand.

Then the DME adds fuel creating a richer mixture more condusive to making HP to satisfy the torque demand of the driver.

At the same time the DME suspends emissions monitoring exiting closed loop mode operation and entering open loop operation. With the right OBD2 test tool one can observe this as it happens by monitoring the OBD2 system status flags and the short term fuel trims. Ignition advance gets adjusted too.

Now about that soot...

There are two converters between each bank of cylinders and the exhaust tip. The slight amount of soot there is more a result of the converter output than anything else.

The converters process the exhaust gases quite thoroughly and as a result they generate combustion byproducts and they really have their work cut out for them at engine start and as they warm up. They are fed -- on purpose -- an excess of gasoline -- with air courtesy of the secondary air injection system -- to help them warm up quicker. During this warm up phase they are transitioning from non-functioning cold gatherings of steel and catalyst metals to the hot (600C and hotter where they work best) little furnaces they are.

Soot is the byproduct of this.

My cars have it and don't bother to clean the tips on a regular basis. I have cleaned them a few (very few times) and they regain their thin coating of soot in almost no time when the engine restarted and allowed to run.

The soot doesn't keep collecting/building up, it just doesn't go away.

All IC engines produce this soot and all cars have this layer of soot. It is just more visible with our Porsches due to the shape of the exhaust tips which are more open giving us a peak at these areas less visible in other cars.

As long as the engine is running ok as long as the CEL is off there is nothing of any interest to see at the exhaust tips.

The much more interesting view is out the windshield from behind the wheel.