Direct injection?

Anyone have any really long term experience with a car featuring direct injection?

I've noticed several manufacturers have added port injection to engines that were previously direct injected....Ford and Toyota.

I bought a car last week with an " extended test drive " but have decided that I am not all that crazy about it.  One reason why I bought this particular car was that it didn't have direct injection, while nearly every other newer car at this dealership seemed to be direct injected.

Also need to consider a vehicle with a " H point " higher than your run of the mill sedan. (Small truck, SUV, CUV)

What is it specifically you're worried about?

Carbon build up is a thing. On the GTIs for example they say you can avoid it by periodically driving the car above 3000 rpm for at least an hour at a time. That's pretty much my use case so I haven't worried about it. On the PCA website they recommend the 2009 base Cayman or Boxster over the S as a daily driver because the S is direct injected. 

Some are better than others

I understand that some mfgs have "solved" the carbon build-up problem by adding traditional injectors in addition to the cylinder injectors. Point being, if a car is touted as direct-injection, it may or may not have the extra injectors to avoid any issues.

kb58 said:

 I understand that some mfgs have "solved" the carbon build-up problem by adding traditional injectors in addition to the cylinder injectors. Point being, if a car is touted as direct-injection, it may or may not have the extra injectors to avoid any issues.

That is for emissions, not carbon buildup, though.  I'm sure alfadriver will be along shortly to explain further.    I don't design the things, I just have to figure out why they fail.

For carbon, they are spending more care in engineering the PCV system to eject as much oil as possible, and I've heard of deliberately timing fuel injection so some will blow back up the intake.

To the OP, DI is pretty much the standard now, port injection is kind of rare.  There are millions of miles of DI experience.  It's a lot like electric power steering.  It felt like in the space of about one product cycle ten-ish years ago, it went from rare to utterly common.

I've only had two DI engines apart, a 90k mile VWAG 2.0 turbo engine (ate timing chains, bent all the valves) and a I forget how many miles Chevy 5.3 (lifter failure).  In both cases the carbon was nothing to get excited about, they looked about normal.

In reply to Pete. (l33t FS) :

Yup, the PFI injector is 90% emissions, 10% power (some may remember that DI injection systems are volume limited....)  While I can't be specific, the combination of PFI, and multiple DI injections do wonders for the cold start emissions.  But thanks for posting that- spot on.

Pre PFI injectors added- the carbon build up was very variable depending on who made the engine.

That being said, Ford has had DI in production since 2010, and in pretty high volume production since 2011.  That I'm aware of, there have been few DI related issues over the last decade.

In reply to alfadriver :

We used to have this local technicians' association where we'd share information and about once a month would have a meeting with a guest speaker.  One of said speakers was a Ford trainer, or maybe a Ford trainer trainer.  One of the things he pointed out was that Ford was using Bosch, just like practically everyone else on the planet.  But, Ford sprung for the top tier of injector tolerance, for much greater consistency and reliability.  

I have never had to replace injectors on a Ford, but the way he said it, you took them out of the package, installed them in the head, and you're done.  Other manufacturers, you need to enter the new injectors' calibration codes in the PCM.  Or, like the Mazda DISI that I'd dealt with (only DI injector failure I have first person experience with) you compare the letter codes of the old injectors to the new ones, and try to match up letters and/or get the letters as close to the old ones as you can.  Kinda hokey.

In reply to Pete. (l33t FS) :

That's actually pretty accurate.  Or very accurate.  Bosch still makes the best DI injectors, and the rest have not figured out how they do it- even when they "replicate" the process, they fall short.

The brand of gas you use in a DI engine has a lot to do with carbon build-up.  The latest issue of GRM touches on Top Tier fuels.

In reply to racerfink :

I think that I read pretty much the same thing (about brand of gas) here on this board before.

I recently traded in my 09 P71 that on my mechanic's recommendation I ran on premium gas.  Between the mediocre gas mileage (20-21 or 22) and the high cost of premium (about $3.45/gallon BEFORE this pipeline hack) I felt like I was putting a small fortune in the tank at fill-up.  So, as the OP says, I looked at a newer car.  I tried to avoid direct injection when looking at cars because of the (possible?) carbon build-up " problem ".

BTW, Toyota's 1.8 in the Corolla is still port injected while the same car with the 2 liter has port and direct injection.  

So other manufacturers engines (I did notice a few Fords were doing 2 injection systems) are also using both...just not publicizing it ?

And using name brand gasoline (I use Shell fairly consistently) should alleviate any problems ?

65K miles on my 2016 MX-5 and no issues.

In reply to racerfink :

The type of gas used has no impact on the amount of carbon build up on the valves.  The fuel is injected directly into the combustion chamber, there is no chance for it to "clean" the valves.

Almost 90k miles on my DI fiesta st, largely on 87 octane. It did eat a throttle body a while ago, probably at least partially from carbon buildup. But I'm not sure port injection would have helped with that since that's still post throttle body. Doesn't seem to have noticably lost any fuel efficiency.

Valves don’t fully open and close in a nanosecond, and they certainly don’t do it in the time  the piston is stationary.  Which is why the additives in top tier gas matter in a DI car.

Doing the math.... we've put a combined 90k miles on Korean DI engines. I seafoam every 30k. Do extended OCI's and buy the cheapest gas. DI engines don't bother me. personally I enjoy the 138hp and 38mpg out of the 1.6

racerfink said:

Valves don’t fully open and close in a nanosecond, and they certainly don’t do it in the time  the piston is stationary.  Which is why the additives in top tier gas matter in a DI car.

For DI only cars, the fuel still does not clean the valves- so the onus is on the PCV system to keep it clear of anything that will stay on the valves.

DI injection mostly happens with the intake valve is open, so the flow of the air very much prevents the fuel from backflowing into the intake system.  And the duration is short enough that it's mostly done before halfway down from TDC on the intake stroke.  For the pushback portion of a nominal stroke- the fuel that is there is mostly evaporated  and would not wash the valve.

The additives in top tier fuel will help with the localized deposits around the injector.  But even those are more about the injector design and how they work vs. the fuel- as injectors that dribble a little bit of fuel (and there are some makers that do that) will deposit heavier than ones that don't- regardless of the fuel.

You are right that injectors don't operate in a nanosecond, but they mostly do less than 5 ms.

In reply to alfadriver :

and a lot of the deposits are from crappy oil or over extended OCI's as well. The oil reaches its limit on protection and starts to break down, overloading the PCV and getting into the intake tract.

Even with good OCI no port fuel and some interesting vvt strategies can cause issues. The VW over time got much better as they tuned the engines differnently over time. My port injected 3.6 VR6 is the cleanest I have seen, especially using methanol 

I have worked at a very busy Ford dealer since DI cars hit the market. We have NEVER seen a drivability issue caused by carbon buildup. 

I think it would depend on the manufacturer.

VW/Audi Ive seen massive carbon build up issues. Generally requiring walnut blasting, from 4.2s to 2.0

Mazda, I havent seen any carbon related issues. Ive seen very high mileage 3s and there is definitely some build up but nothing causing problems.

Toyota I havent seen a problem

GM Ive seen a few carbon problems, but have solved all of them with a basic top end cleaning.

About the only DI engine Id worry about is a VW/Audi. Everything else Id use good oil, change it regularly, do an occasional top end clean and beat on it regularly, and never think twice about it

Media blasting the ports every decade or so should take care of intake port build up. It can be an issue on engines like the Ecotec.

We keep seeing people feeding gasoline additives to the tank to deal with this despite the fact that gas never touches the intake ports.

In reply to Opti :

Wouldn't "beat on it regularly" INcrease problems, because of increased blowby?

But then it would also keep the rings from sticking, which is worse for blowby.  (Kif, we have a conundrum!)

All the horror stories from VWAG engines are wild to look at pictures of, but my only actual experience with massive carboning... is with TDI engines, where you could scrape about a liter of carbon out of the intake manifold.  (I know this, because I done it. Several times...)  

i wonder what people are doing with the TFSI engines that aren't having issues that is different from the ones that are.

Pete. (l33t FS) said:

In reply to Opti :

i wonder what people are doing with the TFSI engines that aren't having issues that is different from the ones that are.

From my post above: "On the GTIs for example they say you can avoid it by periodically driving the car above 3000 rpm for at least an hour at a time." I believe this recommendation came from VW USA.

Mercedes started using direct injection in automotive gasoline engines in 1948. I think we have it sorted out now.