Planet 9

rocket · #1 04-25-2009, 05:42 PM

These pics are from a 2008 Porsche cayenne turbo (DFI engine). Apparently this is a very common issue. Also showing up on a lot of Audi DI engines.

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

longfoot · #2 04-25-2009, 05:51 PM

Wow! Can you explain further? This looks like some very poor combustion...

**jaica** · #3 04-25-2009, 06:01 PM

Ouch! Looks like a very expensive and recurring expense, even if at first it is covered by waranty.

gtscayman · #4 04-25-2009, 06:11 PM

Put some Shell nitrogen enhanced gasoline in there and it'll clean right up!

Tomasz · #5 04-25-2009, 06:16 PM

Yes, this has been discussed before. This is mostly a US problem as well. Seems that in order to achieve US emission standards our cars run rich. I do not understand why, beyond what I heard and posted here. Also, on non DFI engines the injection of gas appears to clan the valves, while on DFI it does not. Again, someone more technical could explain further. For these two reasons, DFI engines in US are having major carbon build up issues. It is likely that Softronic or similiar flash will help with the issue by properly leaning out the mixture. I am not sure if it will be a 100% fix.

It would be wise, to wait two or three years before buying a Porsche DFI car. But not all are that patient.

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

echoboy · #6 04-25-2009, 06:42 PM

That looks simply FUGLY! whew, thank goodness I didn't wait to buy a DFI (i realize that these pix do not constitute direct evidence, but I'm trying to make myself better

)

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

boobernackle · #7 04-25-2009, 06:50 PM

According to Porsche, this is not a defect at all. They will be announcing a new "feature" that happens to address this issue in the 2011 models. This is a part of the car design, like the trunk clunk, engine smoke and others.

**Craig@Rennstore.com** · #8 04-25-2009, 06:59 PM

You've GOT to wonder - aren't these things TESTED prior to introduction???? Jeepers...

Rockster · #9 04-25-2009, 07:05 PM

Originally Posted by Tomasz

Yes, this has been discussed before. This is mostly a US problem as well. Seems that in order to achieve US emission standards our cars run rich. I do not understand why, beyond what I heard and posted here. Also, on non DFI engines the injection of gas appears to clan the valves, while on DFI it does not. Again, someone more technical could explain further. For these two reasons, DFI engines in US are having major carbon build up issues. It is likely that Softronic or similiar flash will help with the issue by properly leaning out the mixture. I am not sure if it will be a 100% fix.

It would be wise, to wait two or three years before buying a Porsche DFI car. But not all are that patient.

and this is the ideal mixture of air:fuel for a properly functioning converter to most fully process exhaust gases into something less harmful.

Just a bit either side of this ratio and converter efficiency goes down and emissions go up.

The engine controller is basically tasked with ensuring the engine receives this 14.7:1 air:fuel ratio in order to keep emissions below some unacceptable threshold.

Under some circumstances the engine controller can venture outside of this 14.7:1 ratio such as in cold starts or under heavy acceleration (or under closed throttle deacceleration).

14.7:1 is good for the converters but bad for the engine, well bad in that a gasoline engine develops more power with a slighly richer mixture.

Direct injection engines attempt to deliver a richer mixture of air:fuel to the combustion chamber but in a small cloud centered around the spark plug.

Away from the cloud there is an excess of air and a dearth of gasoline.

The "rich" cloud delivers better utilization of gasoline and more power, while the air outside of this could provides excess air (oxygen) to the converters. The converters need oxygen to use to process (through chemical reactions) the more harmful exhaust gases into less harmful exhaust gases.

One particularly bad gas is Nox. Nitrogen oxide. If forms in the high temperatures of combustion. To keep this temp down engines are designed to under some operating conditions to allow some mixing of exhaust gases with the fresh incoming charge. Intake and exhaust valve overlap is one such way.

A side effect is some of the cloud and some exhaust gases can flow back into the intake ports and leave deposits on the intake valves. Since fuel injectors are no longer spraying fuel on these surfaces there's nothing to wash these deposits off.

The intake sides of the intake valves are crucial to the proper flow and swirling of incoming air to form the pre-cloud around the spark plug/fuel injector into which fuel will be injected.

Deposits on these intake valve surfaces will affect the proper formation of this cloud and in fact likely lead to even more deposits as the cloud ventures outside of its intended area of existence.

The problem is exacrebated by mainly the way we in USA drive our vehicles. Lots of idling and low rpm useage. Most engines spend their time operating at 30% of throttle or less and under these conditions it is more likely air flow in the combustion chamber will be backwards and purposely so. Over time build up will occur.

Couple of things you can do to help engine:

1) Do not overfill engine with oil. Overfilling causes more oil vapor to get into the crankcase air and more oil vapor to remain in the air that passes through the oil recovery system designed to remove oil from this air on its way to the intake system and combustion chambers. This oil vapor in the air from the crankcase being routed to the intake and combustion chambers contributes to the build up of deposits on the valves.

2) Keep engine oil fresh. Old oil will accumulate water and unburned gas over time and this makes oil more fluid and this results in more oil foaming and more oil foaming results in more oil vapor in crankcause fumes. More oil in these fumes means more oil vapor routed to engine intake and more deposits.

3) Avoid long periods of idling.

3) Use higher engine rpms. Granted this one's tough cause we are all seeking to use lower engine rpms to mainly save fuel. One doesn't have to run engine to redline every shift but any bit of extra engine rpms helps.

Sort of related: A problem developed with VW's diesel engines. VW used exhaust gas recirculation to feed exhaust gases into the intake to essentially pollute the incoming air and lower its oxygen content and thus lower combustion chamber temperature and Nox creation.

The problem was 1) This (diesel) exhaust gas contained soot; 2) This soot mixed with crankcase fumes that contained some oil vapor and the soot and oil combined to in some cases form a hard layer of carbon (soot/oil) in the intake passages that in some cases limit intake air flow into the engine to the point the car would barely run.

The fix was an intake cleaning. That was not covered under warranty.

The solution was to run a good quality diesel engine oil. Change it frequently. Avoid overfilling the engine with oil.

And contrary to what many buyers felt was proper for the engine, to use more rpms, not fewer. Those that attempted to drive the car like a big rig and short shift and keep rpms low, below 2000 and even lower in some cases would find the engine coked up in sometimes 30,000 miles or even less.

OTOH those that followed the above solution -- of which I was one -- found upon inspection while the intake manifold passages had a layer of oil there was no build up and the intake passages were quite open. I drove my VW TDi for over 120,000 miles and never had a problem. Based on the way the woman I sold it too was driving it -- shifting at just 1500 rpms -- I expect it coked up on her pretty quick.

Anyhow, back to Porsche. I have heard rumors -- just rumors --the solution for DFI engines that develop this build up and it will not go away on its own -- is to develop an intake system cleaning process that consists of fitting a temporary tank of cleaning fluid to the engine's intake system and as the engine runs (at idle, or at some higher speed I do not know) feed this fluid into the intake system.

The fluid removes deposits upstream from the combustion chamber and of course in the chamber and beyond. An oil/filter change will almost certainly be required after this cleaning process.

My advice would be to attempt to use the vehicle/drive the vehicle in such a way as to avoid the build up. As I did with my VW. And in doing so I found engine fuel economy didn't suffer. Over 120,000+ miles of driving that engine delivered a reliable/consistent 40+ mpgs in all kinds of driving, from slogging through stop/go driving, to high speed highway runs in all sorts of weather.

These DFI engines I think will deliver better fuel economy even if driven in this manner and this will help to keep the intakes clear of deposits. Any deposits will almost certainly affect fuel economy so nothing's lost by being a bit more "agressive" with the engine's rpms. And much is to be gained. If (when) engine deposits accumulate fuel economy will go down and the symptom worsen.

Sincerely,

Rockster.

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

echoboy · #10 04-25-2009, 07:44 PM

Rockster, nice summary! thanks

**madcow** · #11 04-25-2009, 08:33 PM

Crappy us gas.

rocket · #12 04-25-2009, 08:38 PM

Originally Posted by echoboy

rockster, nice summary! Thanks

+1 .

PBJT · #13 04-26-2009, 02:13 AM

Agree with most of your points but I work on VW and your comments are not 100% of the story. Not everything you learned fully translates to gas DFI and not for the same reasons. Some do. Many feel DFI engine buildup is a combination of poor quality fuel, too much idling, and PVC oil mist. My comments in bold.

Originally Posted by Rockster

Sort of related: A problem developed with VW's diesel engines. VW used exhaust gas recirculation....

Many cars use EGR, it's not unique to VW diesels and not totally the fault of the engine.

The problem was 1) This (diesel) exhaust gas contained soot; 2) This soot mixed with crankcase fumes....

They also have tons of piston blowby from high compression and cold starts. The oil mist is so heavy that people find a significant amount of oil pooled at the low spots of the intake tract. There is no oil seperator / trap to let the oil pool back into the crankcase. The other cause is fuel quality. The new cleaner diesel fuel sold in the US greatly reduces this problem. Biodiesel users say that there's almost no soot buildup in the intake.

And contrary to what many buyers felt was proper for the engine, to use more rpms, not fewer. Those that attempted to drive the car like a big rig and short shift and keep rpms low, below 2000 and even lower in some cases would find the engine coked up in sometimes 30,000 miles or even less.

This is probably the most relevent but it's not just rpm, it's also higher exhaust gas temps that clean out the soot and buildup. Diesels run cooler so higher EGT help burn up and blow out engine buildup. Adding to the problem-modern VW diesels have very high EGR to meet emissions - it can be as much as 30% of the intake air at idle since diesels run super lean. Higher RPM/load reduces EGR in that car.

My best guess is that high rpm and load could help burn up sooty deposits in gas DFI as well. I'm sure 95% of drivers don't run hard onto the highway on ramp and only rev through the full engine rpm once or twice. I've heard US gasoline doesn't help DFI buildup but not sure on this one.

Seafoam is great for cleaning up engine deposits.

Audi DFI use an oil cyclone seperator to get as much oil out of the PVC system but it's not 100% effective and many believe it's a contributing factor to DFI related valve buildup. Any PVC breather to the open air is not emissions legal and an oil dump tube to the ground will probably wipe out a few bikers

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

Rockster · #14 04-26-2009, 04:11 AM

Originally Posted by Fluids

Agree with most of your points but I work on VW and your comments are not 100% of the story. Not everything you learned fully translates to gas DFI and not for the same reasons. Some do. Many feel DFI engine buildup is a combination of poor quality fuel, too much idling, and PVC oil mist. My comments in bold.

My best guess is that high rpm and load could help burn up sooty deposits in gas DFI as well. I'm sure 95% of drivers don't run hard onto the highway on ramp and only rev through the full engine rpm once or twice. I've heard US gasoline doesn't help DFI buildup but not sure on this one.

Seafoam is great for cleaning up engine deposits.

Audi DFI use an oil cyclone seperator to get as much oil out of the PVC system but it's not 100% effective and many believe it's a contributing factor to DFI related valve buildup. Any PVC breather to the open air is not emissions legal and an oil dump tube to the ground will probably wipe out a few bikers

was that VW didn't have any means to filter out soot and the air/oil separator for the TDi was junk. Diesels of course suffer huge amount of blowby and the TDi being turbo-charged only added to this. Oil would soot up, darken to black, in just a few hundred miles of running. My '02 Boxster would keep its oil looking just like it did when it came out of the bottle for far longer.

Anyhow, running a better grade of gas might help curb DFI deposits on the intake valves. The gas cleaning benefits severely limited by the fact it is no longer sprayed against the valve surfaces but has to get there if it gets there at all by being carried back into the valve area where it hopefully will help remove deposits. 'course, if one uses a lousy grade of gas this will cause the deposits to increase.

Of course since many believe gas is gas many will continue to use the lowest quality of gas. Gas is a vital fluid too just like oil or coolant yet many dismiss it as something less vital and expect/assume the engine will be just fine burning any old thing. (Sort of reminds me of a steam train group that used to collect old engine/lube and cutting oil to burn in the steam train's boiler.)

Porsche has a similar cyclone air/oil separator/defoamer mounted down low in the sump. Oil from the scavange pumps is directed to these cyclones and swirls around with no little violence. Fluid goes low and exits air goes up and exits into the crankcase proper. Still carrying alot of oil in vapor form though.

Here's a pic of one of two in a 996 engine:

The crankcase ventilation system of course keeps the fumes from building up and works to keep pressures lower in the crankcase. This helps lower boiling point of the more volatile liquids in the oil so they boil off and of course their fumes routed to the intake manifold.

The old style crankcase breather tube (draft tube) routed down under the car is terrible. This is one reason why sludge was a problem with older engines. This poor excuse for a crankcase ventilation system allowed water and gas to build up in the oil. Low detergent oil didn't help either. It had to be low detergent cause oil companies hadn't figured out how to produce high detergent oil that didn't entrain a huge amount of air. Even today this is still a problem for some engines that have insufficient means to remove air from oil. In some case at high rpm this oil with air gets into the valve lifters and they soften and valve action becomes poor and high rpm horse power suffers.

Anyhow, engine designers of these DFI engines are going to have to come up with much better designs to remove more oil vapor from the crankcase fumes before these fumes are routed to the intake to be burned.

Or DFI engines will get a bad rap for loading up with deposits that really will impact the critical air flow into the combustion chambers DFI counts on so much to deliver the benefits it delivers when it all works right.

Sincerely,

Rockster.

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

**Krokodil** · #15 04-26-2009, 04:39 AM

Unfortunately the m97.21 engines do not have the cyclone separators that were installed in the m96 engines. Here a link to a single post and pictures describing the differences: http://www.planetporsche.net/345063-post202.html

Cheers,

graphix25 · #16 04-26-2009, 05:36 AM

Like I needed any more reasons to hit red line at least a couple of times a day.

Lucky · #17 04-26-2009, 01:26 PM

Originally Posted by Rockster

and this is the ideal mixture of air:fuel for a properly functioning converter to most fully process exhaust gases into something less harmful.

Just a bit either side of this ratio and converter efficiency goes down and emissions go up.

The engine controller is basically tasked with ensuring the engine receives this 14.7:1 air:fuel ratio in order to keep emissions below some unacceptable threshold.

Under some circumstances the engine controller can venture outside of this 14.7:1 ratio such as in cold starts or under heavy acceleration (or under closed throttle deacceleration).

14.7:1 is good for the converters but bad for the engine, well bad in that a gasoline engine develops more power with a slighly richer mixture.

Direct injection engines attempt to deliver a richer mixture of air:fuel to the combustion chamber but in a small cloud centered around the spark plug.

Away from the cloud there is an excess of air and a dearth of gasoline.

The "rich" cloud delivers better utilization of gasoline and more power, while the air outside of this could provides excess air (oxygen) to the converters. The converters need oxygen to use to process (through chemical reactions) the more harmful exhaust gases into less harmful exhaust gases.

One particularly bad gas is Nox. Nitrogen oxide. If forms in the high temperatures of combustion. To keep this temp down engines are designed to under some operating conditions to allow some mixing of exhaust gases with the fresh incoming charge. Intake and exhaust valve overlap is one such way.

A side effect is some of the cloud and some exhaust gases can flow back into the intake ports and leave deposits on the intake valves. Since fuel injectors are no longer spraying fuel on these surfaces there's nothing to wash these deposits off.

The intake sides of the intake valves are crucial to the proper flow and swirling of incoming air to form the pre-cloud around the spark plug/fuel injector into which fuel will be injected.

Deposits on these intake valve surfaces will affect the proper formation of this cloud and in fact likely lead to even more deposits as the cloud ventures outside of its intended area of existence.

The problem is exacrebated by mainly the way we in USA drive our vehicles. Lots of idling and low rpm useage. Most engines spend their time operating at 30% of throttle or less and under these conditions it is more likely air flow in the combustion chamber will be backwards and purposely so. Over time build up will occur.

Couple of things you can do to help engine:

1) Do not overfill engine with oil. Overfilling causes more oil vapor to get into the crankcase air and more oil vapor to remain in the air that passes through the oil recovery system designed to remove oil from this air on its way to the intake system and combustion chambers. This oil vapor in the air from the crankcase being routed to the intake and combustion chambers contributes to the build up of deposits on the valves.

2) Keep engine oil fresh. Old oil will accumulate water and unburned gas over time and this makes oil more fluid and this results in more oil foaming and more oil foaming results in more oil vapor in crankcause fumes. More oil in these fumes means more oil vapor routed to engine intake and more deposits.

3) Avoid long periods of idling.

3) Use higher engine rpms. Granted this one's tough cause we are all seeking to use lower engine rpms to mainly save fuel. One doesn't have to run engine to redline every shift but any bit of extra engine rpms helps.

Sort of related: A problem developed with VW's diesel engines. VW used exhaust gas recirculation to feed exhaust gases into the intake to essentially pollute the incoming air and lower its oxygen content and thus lower combustion chamber temperature and Nox creation.

The problem was 1) This (diesel) exhaust gas contained soot; 2) This soot mixed with crankcase fumes that contained some oil vapor and the soot and oil combined to in some cases form a hard layer of carbon (soot/oil) in the intake passages that in some cases limit intake air flow into the engine to the point the car would barely run.

The fix was an intake cleaning. That was not covered under warranty.

The solution was to run a good quality diesel engine oil. Change it frequently. Avoid overfilling the engine with oil.

And contrary to what many buyers felt was proper for the engine, to use more rpms, not fewer. Those that attempted to drive the car like a big rig and short shift and keep rpms low, below 2000 and even lower in some cases would find the engine coked up in sometimes 30,000 miles or even less.

OTOH those that followed the above solution -- of which I was one -- found upon inspection while the intake manifold passages had a layer of oil there was no build up and the intake passages were quite open. I drove my VW TDi for over 120,000 miles and never had a problem. Based on the way the woman I sold it too was driving it -- shifting at just 1500 rpms -- I expect it coked up on her pretty quick.

Anyhow, back to Porsche. I have heard rumors -- just rumors --the solution for DFI engines that develop this build up and it will not go away on its own -- is to develop an intake system cleaning process that consists of fitting a temporary tank of cleaning fluid to the engine's intake system and as the engine runs (at idle, or at some higher speed I do not know) feed this fluid into the intake system.

The fluid removes deposits upstream from the combustion chamber and of course in the chamber and beyond. An oil/filter change will almost certainly be required after this cleaning process.

My advice would be to attempt to use the vehicle/drive the vehicle in such a way as to avoid the build up. As I did with my VW. And in doing so I found engine fuel economy didn't suffer. Over 120,000+ miles of driving that engine delivered a reliable/consistent 40+ mpgs in all kinds of driving, from slogging through stop/go driving, to high speed highway runs in all sorts of weather.

These DFI engines I think will deliver better fuel economy even if driven in this manner and this will help to keep the intakes clear of deposits. Any deposits will almost certainly affect fuel economy so nothing's lost by being a bit more "agressive" with the engine's rpms. And much is to be gained. If (when) engine deposits accumulate fuel economy will go down and the symptom worsen.

Sincerely,

Rockster.

Ordering a 2101 CS in June for September delivery. If this were you would this DFI issue stop you from ordering?

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

echoboy · #18 04-26-2009, 01:29 PM

my take is that this is pretty new technology: could be worthwhile to see how things turn out with the DFI's that are already in the Cayennes and 911's. the gunk in the pix makes me wonder how ever passed Porsche's quality control?

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

Lucky · #19 04-26-2009, 01:30 PM

Originally Posted by Fluids

Agree with most of your points but I work on VW and your comments are not 100% of the story. Not everything you learned fully translates to gas DFI and not for the same reasons. Some do. Many feel DFI engine buildup is a combination of poor quality fuel, too much idling, and PVC oil mist. My comments in bold.

My best guess is that high rpm and load could help burn up sooty deposits in gas DFI as well. I'm sure 95% of drivers don't run hard onto the highway on ramp and only rev through the full engine rpm once or twice. I've heard US gasoline doesn't help DFI buildup but not sure on this one.

Seafoam is great for cleaning up engine deposits.

Audi DFI use an oil cyclone seperator to get as much oil out of the PVC system but it's not 100% effective and many believe it's a contributing factor to DFI related valve buildup. Any PVC breather to the open air is not emissions legal and an oil dump tube to the ground will probably wipe out a few bikers

So would you still order a 2010 CS knowing this ?

DFI

Direct Fuel Injection (DFI), is a new technology that Porsche states can cut fuel consumption by up to 15 percent, while increasing power by up to 13 percent. DFI cuts emissions by warming up the catalytic converter more quickly, and ensures a sharper throttle response. Better for your right foot - and the planet, then.

DFI allows much more precise measurement of fuel supply and injection at pressures up to 120 bar; it has numerous combustion modes, with different cycles for cold-starting, low-speed driving and performance driving.

As the name suggests, DFI injects fuel directly into the individual combustion chambers, instead of the intake manifold. The injector valves have an electromagnetic mechanism that controls each injection with astonishing precision, while a high-pressure pump provides the necessary pressure—up to 1,740 psi—to accompany the rapid fire of the fuel injection.

Precise geometry of the injector’s position and its spray pattern is a key factor in helping to improve power, torque and emissions of the engines. The specific placement of the fuel as it enters each chamber creates a swirl that improves the air/fuel mixture, and therefore the overall combustion process.

At engine speeds up to 3500 rpm, a double-injection process is used. In this mode, the required fuel volume is delivered in two successive injections per working stroke. The resulting benefits include faster catalyst warm-up and increased torque in the upper load range.

By forming the air/fuel mix directly in the combustion chamber, DFI contributes to engine cooling. As a result, it is possible to increase the compression ratio and with it the power and efficiency of the engine.

The direct injection process is continuously adjusted. The engine management system reads changes to throttle inputs and performance requirements and, as you drive, the air/fuel mix is monitored and adapted as required. Oxygen sensor circuits within the exhaust system provide accurate emissions control.

zedcat · #20 04-26-2009, 01:55 PM

If you're really worried about it you could consider the 2.9L engine in the base Cayman. It is the new 9A1 design but with conventional FI.