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exhaust soot - oil or fuel???

 
Old 02-10-2011, 09:56 PM
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slicky rick
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Default exhaust soot - oil or fuel???

in our quest to find what the heck it is with oil consumption exhaust soot and other engine issues... My car does not consume oil... i went through the first 10k km without adding a single drop of oil. actually removed some of the oil since dealer over filled first time i took delivery of the car... But i noticed, specially after the 10k km oil change,...there is more exhaust soot. been cleaning the pipes more often.. did not notice doing that before...could it be due to an overfilled crankcase??? could it be that the electronic indicators are not doing the right job of monitoring and the level indicated was actually an overfill and the engine just burns off everything we put in just like in other older porsches were overfilling caused a lot of smoke??? so for those whos seem to consume oil its actually because of an overfill and we keep putting oil and engine keeps burning. im thinking that the dealer overfilled again and engine is burning off the excess. i will keep all posted after i take the car for a longer drive...
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Old 02-11-2011, 11:18 AM
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The soot can come from crankcase oil but can also come from fuel. Do you have a 2009 or later Carrera? If so, you have DI and this might be the cause of the soot. My BMW 535 has DI and there is quite a bit of soot around the tail pipe. DI is basically a similar set up used by Diesel engines. Also, with DI engines there can be a substantial amount of carbon build-up in the intake area of the head. I am not sure but this might also contribute to soot in the tail pipe? Finally, my 2008S ( with port injection) uses very little oil ( approx. 1 qt/ 7000 miles) and I have a slight amount of soot around the tail pipes.
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Old 02-11-2011, 11:34 AM
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this soot issue has been discussed in our forum so many times but the solution has not yet presented itself...just shooting some ideas... because as you say it could be oil or fuel...funny because my car's fuel consumption is low compared to older models and does not consume oil....so which is the cause?
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Old 02-11-2011, 11:57 AM
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The soot is from the car running very rich at normal speeds around town and on the highway. When I track my [email protected] the exhaust tips inside turn white...just like the GT3 Cups cars exhaust tips....this is optimal and normal.

I've heard of some guys getting the ECU re-programmed from Softronic, EvomsIt and so forth and the car soot's less around town but I have not witnessed this for myself plus a ECU re-program will voide the warranty of the powertrain.
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Old 02-11-2011, 02:41 PM
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As Mike says what the OP sees is probably due to running rich - which always happens in slow driving. In any case, I have yet to see a car that does not have a film of dark dust in the rear after a while, especially high speed driving. and that film is mostly due to brake dust (which is oily), settling in the rear due to the vacuum created by the airflow. Have you considered that?

P.S. - Macster corrected my wrong conventional wisdom big time. Slow driving less rich but slow exhaust velocity - higher soot deposition. Thanks Macster!

Last edited by ADias; 02-12-2011 at 07:08 PM.
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Old 02-11-2011, 03:01 PM
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Originally Posted by slicky rick View Post
this soot issue has been discussed in our forum so many times but the solution has not yet presented itself...just shooting some ideas... because as you say it could be oil or fuel...funny because my car's fuel consumption is low compared to older models and does not consume oil....so which is the cause?
One can have low fuel consumption or run lean and still produce soot. Traditional Diesels are known for running lean and still producing soot. I sometimes wonder if the new cars produce more soot to get around the CO2 emmissions standards that are getting more strict in Europe.

I wonder that since the DI engines inject the fuel into the combuston chamber rather than in the intake area befoe the valve that there is a bit less time to get the fuel adequately distributed before the spark resulting in micro rich areas leaving carbon particles behind.
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Old 02-11-2011, 06:35 PM
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Some additional info....

http://bznotes.wordpress.com/2007/01...n-gdi-engines/

also on pages 22 and 23 of the paper on the site below ( a bit detailed) discuss the issues of combustion with DI engines...it all seems to be related to inadequate fuel distribution of fuel in the air.

http://oxford.academia.edu/LongfeiCh...ection_Engines
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Old 02-11-2011, 08:10 PM
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Originally Posted by slicky rick View Post
in our quest to find what the heck it is with oil consumption exhaust soot and other engine issues... My car does not consume oil... i went through the first 10k km without adding a single drop of oil. actually removed some of the oil since dealer over filled first time i took delivery of the car... But i noticed, specially after the 10k km oil change,...there is more exhaust soot. been cleaning the pipes more often.. did not notice doing that before...could it be due to an overfilled crankcase??? could it be that the electronic indicators are not doing the right job of monitoring and the level indicated was actually an overfill and the engine just burns off everything we put in just like in other older porsches were overfilling caused a lot of smoke??? so for those whos seem to consume oil its actually because of an overfill and we keep putting oil and engine keeps burning. im thinking that the dealer overfilled again and engine is burning off the excess. i will keep all posted after i take the car for a longer drive...
Your car has a serious problem. It is owned by someone who spends too much time staring at its exhaust pipe outlets and not enough time staring through the windshield from behind the wheel.

If there was anything wrong the fuel consumption, oil consumption, exhaust smoke, a CEL or just general (or specific) engine symptoms would be present.

Soot at the exhaust tips is normal. All IC engines produce soot as a by-product of their burning gasoline/diesel/whatever and this soot will collect on the exhaust outlets.

Sincerely,

Macster.
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Old 02-11-2011, 08:15 PM
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hahaha i like that Macster. i guess that the problem with these cars... the weakest link is the nut behind the wheel....somethings always loose
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Old 02-11-2011, 08:23 PM
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one thing i noticed though. it seems that the direction that mike is saying could be right... this soot i noticed when i tried to do economy runs on the highway doing from 60 to 120 kph and cruising with no exciting accelerations. i did 12.5 kms to a liter which i think was very good. i will try to get some acceleration into my drive later and see if it does anything... prior to the oil change i would always do spirited driving and produced very little soot... maximum speed 232kph and regular runs to 200kph now im cruising at 100 so maybe the engine is asking what the f... are you doing?..sissy. if this was the case can you imagine how much more economical our cars would run if Porsche also managed to control the richness of the mix when cruising or just puttering around town...
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Old 02-12-2011, 05:49 PM
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Originally Posted by mdrums View Post
The soot is from the car running very rich at normal speeds around town and on the highway. When I track my [email protected] the exhaust tips inside turn white...just like the GT3 Cups cars exhaust tips....this is optimal and normal.

I've heard of some guys getting the ECU re-programmed from Softronic, EvomsIt and so forth and the car soot's less around town but I have not witnessed this for myself plus a ECU re-program will voide the warranty of the powertrain.
Sorry, but no.

Around town the engine's being fed an air:fuel ratio of 14.7:1 (actually within a very narrow window on either side of this ratio) cause the engine produces the best exhaust gases for the converters. The converters have a very narrow window of exhaust gas make up in which they can most completely post-process the exhaust gases.

On the track -- or even on the street -- the engine controller unit (Ecu) can deviate from the 14.7:1 ratio moving to a richer mixture to satisfy the driver's torque demands. (You can tell when the Ecu does this by noting when it moves from closed loop operation to open loop operation.)

Thus almost certainly because of the high torque demands made by the driver on the track the engine is running a *richer* mixture than it would running around town.

The reason the soot appears around town and disappears after some track time at the track there is the higher exhaust gas flow which works to expel the soot before it can collect and blast off any that does collect; the higher (and more prolonged) exhaust gas temperature which works to burn the soot in the exhaust gases before it can collect.

The white exhaust tips are normal for track driving, but are not optimal nor are they gonna happen on a car driven on the street, unless one can manage to drive the car on the street like he drives it on the track.

Might add that Porsche is very good at controlling the fuel mixture at all times, and around town especially. Most cars spend the bulk of their time operating at 30% load or less so efficient operation at these lower loads is paramount to ensuring drivers enjoy the car, do not take exception to its behavior at part throttle around town driving.

When I drive my 03 Turbo reasonably sane (as I do always) fuel consumption drops and the on-board computer display mpg number creeps up to over 20mpg and can reach nearly 24mpg.

If I get even a bit agressive with the throttle that mpg reading can drop faster than Mubarek's popularity.

The Turbo doesn't have it but my 06 GTO had an instantaneous mpg readout and I could easily with agressive driving get that thing into single digits (ouch!). But on steady state cruising in a high gear with engine rpms low the instantaneous mpg reading would sometimes get into the mid-30mpg range.

Sincerely,

Macster.
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Old 02-12-2011, 07:04 PM
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Originally Posted by Macster View Post
Sorry, but no.

Around town the engine's being fed an air:fuel ratio of 14.7:1 (actually within a very narrow window on either side of this ratio) cause the engine produces the best exhaust gases for the converters. The converters have a very narrow window of exhaust gas make up in which they can most completely post-process the exhaust gases.

On the track -- or even on the street -- the engine controller unit (Ecu) can deviate from the 14.7:1 ratio moving to a richer mixture to satisfy the driver's torque demands. (You can tell when the Ecu does this by noting when it moves from closed loop operation to open loop operation.)

Thus almost certainly because of the high torque demands made by the driver on the track the engine is running a *richer* mixture than it would running around town.

The reason the soot appears around town and disappears after some track time at the track there is the higher exhaust gas flow which works to expel the soot before it can collect and blast off any that does collect; the higher (and more prolonged) exhaust gas temperature which works to burn the soot in the exhaust gases before it can collect.

The white exhaust tips are normal for track driving, but are not optimal nor are they gonna happen on a car driven on the street, unless one can manage to drive the car on the street like he drives it on the track.

Might add that Porsche is very good at controlling the fuel mixture at all times, and around town especially. Most cars spend the bulk of their time operating at 30% load or less so efficient operation at these lower loads is paramount to ensuring drivers enjoy the car, do not take exception to its behavior at part throttle around town driving.

When I drive my 03 Turbo reasonably sane (as I do always) fuel consumption drops and the on-board computer display mpg number creeps up to over 20mpg and can reach nearly 24mpg.

If I get even a bit agressive with the throttle that mpg reading can drop faster than Mubarek's popularity.

The Turbo doesn't have it but my 06 GTO had an instantaneous mpg readout and I could easily with agressive driving get that thing into single digits (ouch!). But on steady state cruising in a high gear with engine rpms low the instantaneous mpg reading would sometimes get into the mid-30mpg range.

Sincerely,

Macster.
Excellent stuff!
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Old 02-12-2011, 10:18 PM
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The more I read some of these threads the more I realize how little I know.
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Old 02-12-2011, 10:44 PM
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Originally Posted by Macster View Post
Your car has a serious problem. It is owned by someone who spends too much time staring at its exhaust pipe outlets and not enough time staring through the windshield from behind the wheel.

If there was anything wrong the fuel consumption, oil consumption, exhaust smoke, a CEL or just general (or specific) engine symptoms would be present.

Soot at the exhaust tips is normal. All IC engines produce soot as a by-product of their burning gasoline/diesel/whatever and this soot will collect on the exhaust outlets.

Sincerely,

Macster.
+1
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Old 02-12-2011, 10:54 PM
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So no...to exactly what?....the white exhaust tips means what...compared to the black sooty exhaust tips? Obviously there is a different burn, correct? You went off talking about fuel mileage of your Turbo.

I understand the soot not sticking to the exhaust tips at the track but then why do they turn white? I noticed that the GT3 Patron and Grand Am Porsche's all have this whiteish look inside the exhaust tips.

I'm no expert here but from asking around the garages at races and so forth I've been told that this is one way to see if the car's fuel burn is correct. Although I've heard a brownish rust color is prefered also but I heard about that in the V8 American car circles.

Originally Posted by Macster View Post
Sorry, but no.

Around town the engine's being fed an air:fuel ratio of 14.7:1 (actually within a very narrow window on either side of this ratio) cause the engine produces the best exhaust gases for the converters. The converters have a very narrow window of exhaust gas make up in which they can most completely post-process the exhaust gases.

On the track -- or even on the street -- the engine controller unit (Ecu) can deviate from the 14.7:1 ratio moving to a richer mixture to satisfy the driver's torque demands. (You can tell when the Ecu does this by noting when it moves from closed loop operation to open loop operation.)

Thus almost certainly because of the high torque demands made by the driver on the track the engine is running a *richer* mixture than it would running around town.

The reason the soot appears around town and disappears after some track time at the track there is the higher exhaust gas flow which works to expel the soot before it can collect and blast off any that does collect; the higher (and more prolonged) exhaust gas temperature which works to burn the soot in the exhaust gases before it can collect.

The white exhaust tips are normal for track driving, but are not optimal nor are they gonna happen on a car driven on the street, unless one can manage to drive the car on the street like he drives it on the track.

Might add that Porsche is very good at controlling the fuel mixture at all times, and around town especially. Most cars spend the bulk of their time operating at 30% load or less so efficient operation at these lower loads is paramount to ensuring drivers enjoy the car, do not take exception to its behavior at part throttle around town driving.

When I drive my 03 Turbo reasonably sane (as I do always) fuel consumption drops and the on-board computer display mpg number creeps up to over 20mpg and can reach nearly 24mpg.

If I get even a bit agressive with the throttle that mpg reading can drop faster than Mubarek's popularity.

The Turbo doesn't have it but my 06 GTO had an instantaneous mpg readout and I could easily with agressive driving get that thing into single digits (ouch!). But on steady state cruising in a high gear with engine rpms low the instantaneous mpg reading would sometimes get into the mid-30mpg range.

Sincerely,

Macster.
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