14.5-14.9 AFR is basically a perfectly clean burn (right stoichiometric ratio), most vehicles will target this during low-normal engine loads. At WOT (wide open throttle) this can typically drop down into the 11-12 AFR range depending on the vehicle (I haven't actually done any data logging on the NX yet) which is going to be more sooty but not excessively rich to kill a catalytic converter. The bit of excess build up at WOT is burned off during normal driving. If you get down into the sub 10 AFR range and are doing this very frequently, then you will start to eat into a catalytic converters life due to the excessive build up that can't get burned off.

In reality, all turbo engines will run a little rich if you're driving them hard, yes the tips will get dirty, but it's nothing to be concerned about...frankly just let them get dark and go for the blacked out tip look instead

 

I use premium gas as recommended, and haven't noticed any buildup around the exhaust.

 

I've always used premium, normally Shell or BP. No excess carbon buildup in 6 months.

 

Yes sir , I don't need a scope or fancy analyser to tell me how dirty a DI engine runs. Looking at the soot painting of the car's behind give me a very good perpective.
Ive been driving in heavy traffic everyday for over 20 years and I reared at least every car made in north America (SUVs) produced for me car's year at least once if not more.

VW ( Diesel , Non diesels turbo (DI) , and Lexus DI stands right out of the lot. (non suv, trucks , muscle cars, big monsters, lambo, dont count here)

There will always be a black car sheep proving me wrong, but If I didnt see it, its because its a black sheep

 

Yes and no. All of today's engines are run rich. It is to counter the excessive heat from raising the operating temps to decrease emissions. The soot you're seeing is more from post EGR fuel residuals and valve overlap.


eventually the engine will have issues in due time from this.

You best bet is to run a quality oil that increases ring cylinder seal and provides a better film on the valve guides enough to reduce the post EGR fuel residuals and fuel vapors being recirculated through the PCV system. A quality fuel helps greatly, you can also run E15 on the NX safely and this can combat some of the deposits that the gasahol leaves behind everywhere.

 

EGR/PCV is only a fraction of what a rich burn does to the exhaust tips...In several months of driving you'd be lucky to get a quart through the PCV system, most of which would be water vapour. Having run catch cans on other vehicles, they have had zero effect on the amount of soot build up on the exhaust. The majority is from running rich.

E15 will just result in worse fuel economy and ethanol in higher quantities isn't good for the fuel side of things (especially with direct injection and the hpfp, gums them up). Better off just running an E0 premium fuel, I personally use Shell 91 which is ethanol free up here.

 

I'd agree about the quart through the PCV system, but it's not water vapor, I've done numberous UOA on what these catch cans are catching and it's as predicted a highly diluted oil with lots of fuel. The oil in today's chemistries try to contain the fuel aromatics, additives and water. Theory is it'll burn off easier through the PCV. Problem is today's fuel's aromatics are sticking to the oil unlike ever before. As this oil/fuel blend is cycled through the PCV system, the engine will automatically pull back on the timing. Whether said user compensates by dumping more fuel, I wouldn't know in this case. Now the EGR will work harder. He likely has poor ring seal, most of the engines today have poor ring seal as engineers have to compromise on emissions, performance and fuel economy, and since these engines run hot to reduce the emissions, they run overly rich, as you also mentioned. They use poor quality oil and fuels with poor ring seal in the combustion cyclinder decreasing efficiency and poor valve guide film seal, increasing the amount of soot, and forcing the PCV to work harder with the EGR as a result. These post EGRed fuel residuals make their way through the exhaust and since we have polar issues, the fuels chemistry will not have solvency with these residuals. I would normally address this issue by chemically treating the engine, rather than trying to do anything that really won't help or work. It's doubtful the OP will have his factory ECU tuned, nor would I recommend it considering we can treat this chemically and achieve same results. A good UOA would quickly figure why it's running the way it is. As you mentioned, I'll agree, it's lot to do with being rich, but you're failing to give the EGR and PCV the impact on overall engine design, I haven't even talked valve overlap and this engine cycles between Otto and Atk.

Shell is a great fuel, I was going to assume you're in Canada but I believe Canada is E5 3/4 of the year. This engine has both direct and port injection. I'm not sure what you base your ethanol claims on, in the US we have always had anhydrous ethanol and even Brazil no longer has hydrous ethanol. Yes, fuel economy will "lower" but very very little. The difference between E0 and E15 is about 4% on the average vehicle. I've never seen the gumming up you speak off, maybe you mean bog? But this is a turbo charged engine, FI engines love ethanol as it advances timing greatly and improves the combustion dynamic efficiency by more effectively closing the gap in the ring seal. Quite a few cars will see a little gain in fuel economy as a result. In my many UOA's and tear downs, ethanol actually clears out the deposits left by gasoline. Will E15 clean out this engine entirely? No, but it will help it a lot more than E0. I have worked extensively with OEM's, never seen an issue with ethanol, it only helps. Like synthetic oils when they first came out, issues arose and were taken care of. Problem is the OEM's don't want to spend the money on injectors, pumps, all the required tuning and additional sensors that need to go in the tank and so forth. You'd probably be looking at an extra $1,500USD per NX to be able to properly run E85, for a fuel that many still don't grasp and is hard to produce. In the US, many stations are already progessively moving towards E15 as any vehicle past 2001 can run it safely. Most vehicles even from 1995 can run E15 without issues.

edit: Ethanol is also much easier on engine internals. I have seen ethanol affect small equipment(snow blowers, lawn mowers, etc) but passenger vehicles are well suited for the ethanol in the gasoline as they have standards and guidelines and are much more robust. Small equipment has no federal guidelines or standards.

 

Very cool post...lots of good info in there. I still think proportionally the soot is coming from rich fuel burn more than PCV/EGR system, but I don't have anything to back this up other than personal observations on other platforms (specifically the Mazdaspeed 3). On that platform, at WOT on stock fuel mapping the thing would blow smoke out the tailpipe constantly and tuning could bring it down substantially but you'd still be in the 12.x AFR area at best at WOT but it did slow the soot build up. Of course there were tradeoffs. As for the E15 issues, it stems from running higher octane blends in vehicles not designed to run it...again on the MS3, often we'd do a mix to get E25-E35 (filling up with both E85 and 91 octane). This let us running some pretty aggressive timing/boost but would mean cleaning of the spill valve and HPFP every year or so to avoid what we called the "black death".

 

You're not wrong, I agree with you, but the bigger issue is with a lower quality oil and fuel causing post EGR residuals to become polar that arn't being tackled. So we have factory rich engines with post EGR residuals that are polar. The EGR is great at polarizing residuals but with a good film and formulation that allows for solvency post combustion with the fuel, you can greatly reduce these effects and often stop them outright entirely. If the OP treats this factory issue of running rich, chemically, he could force the gases and residuals to become solvent and not worry about running rich or his tail pipes blacking out.

Ah yes, that I completely see now. I agree, and it's why I mentioned to stay at E15!!! No phone calls of a tank full of E85!!! lol The Lexus engines have been designed to run E15 from factory for some time now as there is strong believe we're moving very soon to E15 in the US. E25 & + would definately cause premature failure of pumps and components and could cause his engine to bog at redline. I'm trying to get people to get on the E85 bandwagon for the RC F, problem is the $$$. With all the injectors, pumps and tuning, it's just very very expensive. The one downside to having port and direct injection.

I get hammered by other people on these threads for really sticking to Shell fuel, but what few realize, is Shell is one of the only that's been able to address the polarization side of things on the fuels aspect. Their additives really burn much cleaner than everyone elses do, although it should still be noted, fuels in NA are garbage and unregulated. If people actually realized we should be pushing for regulation on the fuels, we would have much for efficient engines. Fuel economy and power would almost instantly go up. Unfortunately, we're stuck with BS emissions control devices that actually deteroiate our equipment faster because we can't push big oil off it's stool. "Emissions", the big 22.