So, I do like the new RDX, even though some of the sporting character of the 1st gen is gone... But why the move to a V6? What I was wondering is why on earth didn't Honda just add direct injection to the existing turbo 4? My argument with the 1st generation was it was perfect in almost every way, but was missing DI. Adding DI would have kept weight and lag down and power and gas mileage up. Lets hope Honda follows the Germans' lead and decides to switch back to a smaller turbo engine with DI.

 

I do agree that Honda needs to get onboard with the DI engines ASAP....Funny how Honda was always on the leading edge when it came to engines and now, its trailing a bit behind. Even the Korean's have DI in their entry level cars. Don't get me wrong, I am not saying the Korean are building better engines than Honda (long term reliability) but I do drive a 2012 Accent (my rain driver when I don't want to drive my 2012 TL or 2013 RDX) and let me tell you, that little engine is slick and sips 5.6l/100km on average (city and highway) (or 42 mpg) - trust me, that is quite impressive. For a car that costs half of what a Prius costs and gets fuel economy that is almost comparable fuel efficiency. I don't want to get flamed but I know when the Japanese cars entered the North American market way back when, they were laughed at, and no one took them seriously....I wonder if we'll look back at the Korean's in the same way. Their earlier cars were horrible but they have come a long way since their earlier years. For the price I am paying for this Accent and the usefulness I get out of it, I am quite happy. Now, don't think for a second that I would replace my TL or RDX for the Accent (lol) Its local driver only and does great at that So again, I agree, I can't wait for Honda's DI engines to come out but their Cylinder De activation does work well on the RDX and gives the best of both world in my opinion. A smooth powerful engine when you need it and fuel effciency when you need it too....

 

what are the Koreans doing for carbon build up?
IIRC, that was one of the reasons why DI is bad.

the new "earth dreams" k2x engine has DI, it would be interesting to see how Honda addressed this.

 

I am not sure...it seems everyone is doing Direct Injection. What are other manufacturers are actually doing about carbon build up? I didn't even know it was an issue. I am not as mechanically inclined as some here...I am more on the detailing side

 

The reason why I am buying the new RDX is because it DOESN'T have a direct injection engine. Coming from a relatively new BMW (2009 335xi), I'm tired of the carbon build up/injector/fuel pump issues associated with DI engines. I'm glad Honda has stuck to its roots.

 

I think they are driven to DI to meet CAFE standards, so if the engine suffers from carbon build up that is a lessor consideration. I guess this just means you need to clean the build up out of the engine on a regular basis. If Honda took so long to develop DI to solve the carbon problem then good for Honda.

I hope they solve the CVT problem too!

 

thanks everyone for your input. I actually was not aware of the carbon buildup issue with DI engines... Interesting... So, as rocketman mentioned- if honda has addressed carbon buildup in their DI design- that's great. Upon a little google research- its seems there is nothing inherently wrong with DI, but the entire engine must be designed specifically for DI to address carbon issues. Good thing I'm not an auto engineer...

 

I dont think Honda has solved the carbon build up problem.

the Mazdaspeed3 guys, install a catch can.

 

So far, no one has completely eliminated carbon deposit issue with DI. IMO the best compromise right now is Toyota's D4-S system, where it combines both direct injection and port injection in one system. It would be interesting to see if Honda has solved the problem.

The thing with carbon deposit build up is that, it doesn't happen over night. It's also not exactly a reliability issue. Most of the time, it just affects negatively on your engine output and fuel efficiency as the mileage piles up. Most manufacturers care about the EPA ratings. They don't care too much how well your car is after 100,000 miles. That's your problem, not theirs. They can always say, "It is normal for power and mpg to decrease as the engine gets older."

Honda actually started using DI in the 1st gen Honda Stream back in 2003. Then later that engine got replaced with an even better R series engine but with no DI. So Honda is not exactly behind in this regard.

 

+1 to that. Direct injection technology still has issues, but with the new emissions standard and a goal of averaging something like 50 mpg across the fleet by year.. 202X, companies are moving to turbos and DI, each bringing a new set of problems as your car ages. Get a NA engine while you still can

 

Carbon build-up is an inherent risk of direct injection. For those that don't understand the problem, gasoline is injected directly into the combustion chamber on a DI engine. Although more efficient, these engines run the risk of carbon build-up around the intake valves. In a conventional port injection engine, the fuel cleans the valves, literally washing away the deposits and keeping things working properly. But once the sticky build-up starts, it becomes a magnet for additional deposits . . . The problem snowballs, and performance slowly deteriorates. Chunks of carbon can even break off and damage the catalytic converter. In some cases the engine needs to be torn apart and cleaned - a slow and very costly process. Audi has been a pioneer in direct injection, and not surprisingly they have also received the highest number of complaints, with some engine designs being more troublesome than others. (Google Audi RS4 or 3.2L V6 carbon build up.) Audi and others claim to be working on potential solutions, and Audi even filed a patent for a system designed to prevent the issue, but as far as I know nothing came of it. Although the cause is known, the problem itself seems to be hit or miss. Top tier fuel is recommended to minimize the potential problems. Some claim fuel additives can help prevent it, but I question that since the fuel never actually contacts the intake valves, and so neither do the additives. Others believe that an occasional pedal-to-the-floor on ramp attack will help clear the deposits. Again, I don't believe there is any proof one way or the other, although at least that regimen can bring a smile. One thing I find curious is that I hear very little about Ford DI engines suffering from carbon build up. The Ford engines make competitive power and torque, and they do so on regular unleaded (premium recommended for max performance). So what are they doing that Audi and Hyundai are not?

 

Direct Injection also tends to make the engine not as smooth, i.e. if you look at the BMW 3 Series its very Diesel Like, and even some Hyundai, Infiniti engines are the same way. Given the size of the RDX and its performance numbers (on par or exceeds competition in both fuel economy and 0-60 times), I don't really think DI was necessary with this car. The new MDX, however given how heavy the car is and they are reducing it from 3.7 to 3.5, DI is more appropriate. Same with the new Accord, it makes sense on a 2.4L 4 cyl. Just my thoughts, but I'm more than happy with VCM and how smooth this new RDX engine is, especially compared to the 2.3T.

 

I don't think Honda's were ever unreliable like the Hyundai Pony's etc, but Hondas were rust buckets back in the early years. What Hyundai is doing is providing excellent good looking product that is rated high along with their counterpart, Kia. My buddy has a Forte and for the price, this is an excellent vehicle with a great interior. Honda, with their Civic, looks great outside, but the interior pales in comparison to the Forte. Look out Honda, Hyundai and Kia are coming and you need to improve your game. That said, I think Honda is starting to get much better looking product out. (CRV and RDX) for starters.

 

Well, Audi is telling their owners to go screw themselves. lol. Well, actually, I don't know what they're telling them now, but originally they didn't admit to any problems. For some people that were getting carbon build-up in their engines well before 20,000 miles, they had to go get it cleaned out for themselves at their own cost from what I recall. Maybe someone else has kept up with the Audi DI "issue"?

 

Very informative post!

I can't remember I read but Ford is also having carbon deposit problem.

Infiniti actually doesn't use direct injection on their V6's. They are just inherently not as smooth as the J series, especially the VQ37.

 

Thanks for the very informative post! One question, if fuel never touches the intake valves, why does carbon build up there? And if only air is coming through the intake valves, what causes the build up? I would have thought carbon build up would be more likely on the injector tip. It has to be hot and surrounded with fuel during injection.

Thanks, Jim

 

The build-up is essentially soot - the remnants of combustion. That's why top tier fuel is recommended; better gasoline = less soot.

One thing I failed to mention in my first post is that Lexus DI engines use both direct and port injection. Not surprisingly, the Lexus engines have largely avoided the build-up problem. DI engines tend to clatter noisily like a diesel, particularly at start up. Adding port fuel injection dramatically reduces the clatter while [indadvertantly?] keeping the intake valves clean. I can only assume there are patent laws preventing others from copying the design.

By the way, I should note that I am not an engineer or mechanic. I simply did a lot of research before buying our Audi. That research led to me passing on the 3.2L V6 and opting instead for the far less troublesome 2.0T.

 

I just read an article at Edmunds that says soot build up on the intake valve stem is the problem (as you explained). That is still incredible to me. The intake valve is closed during the combustion stroke and doesn't open again until the next intake stroke. I don't understand how soot can build up on the intake valve stem.

Confused, Jim

 

There is a point where both intake and exhaust valves are open at the same time. It is called valve overlap. Basically as the exhaust valve closes and the piston slows to change direction the intake valve begins to open so the momentum of the outgoing gasses begin to pull the fresh charge from the intake and purge the cylinder. Back when there was little concern for fuel efficiency or pollution and maximum power was the goal the overlap was so large by design as to allow some fuel to get past the exhaust to cool the valve. Under certain conditions some of the cylinder charge can get past the intake valve before it fully closes.

 

Thanks for reminding me about valve overlap! And I guess even if the intake valve remained closed until the piston was at or beyond top dead center, the intake valve would still open into a combustion chamber full of exhaust gas (and "soot"). It will be interesting to see if the engineers can come up with a solution for this problem.

Jim

 

This thread is great - my other car is a tuned 335i that has to have intake valves cleaned every 35k or so. i assumed my wife's 2011 RDX was DI and was trying to get info on what RDX owners do for carbon, but i'm so happy to find out it's not a DI engine!One less thing to worry about.

 

yeah I am not keen on DI as there is another issue: Injector longevity. Diesel engines that are worked are known for eating injectors for lunch...

 

Another inherent characteristic of direct injection is a longer warm up period in cold weather. Spraying fuel towards the piston top has quite a cooling effect.
I like to be warm in the winter.

 

I guess no one knows yet what Honda has done to avoid carbon build up on their DI engines? There are a lot of them out there now, anyone know? Thanks.