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Author Topic: Does direct Injection cause severe cylinder carbon build up?  (Read 3058 times)

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Offline ChopTop

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Does direct Injection cause severe cylinder carbon build up?
« on: September 23, 2010, 02:21:16 PM »
I was just reading about Subaru new 3rd generation boxer engine that's about to be released.  The peanuts gallery was wondering if it will be direct injection (DI) or not, and someone replied that they hoped not because "most modern direct injection engines have severe carbon build-up problems".  I went like Scooby Doo, Ruh Roh.  Has anyone read or heard anything about this before? 

About the only thing I know for a fact is that after cleaning the inside of my exhaust tailpipes is that it turns black pretty quick (even though I use tier 1 premium gasoline) which I had alway assumed was normal regardless if your engine was DI or not.  But since DI shoots gasoline directly into the cylinders wouldn't the constant friction of the cylinder rings keep the inside of the cylinders clean from carbon build up to a minumum? 

 
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Offline TomatoSoup

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #1 on: September 23, 2010, 02:51:49 PM »
Not sure of the answer to your original question, but carbon doesn't build up on the walls of the cylinder for just the reasons you mention.  It builds on the piston top and cylinder head and valves... flat(ish) areas that are not constantly swept.  Over time can change compression and, when it gets hot, cause pre-ignition and run-on (well, the latter in carburated engines :) )
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Offline tazz

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #2 on: September 23, 2010, 05:42:43 PM »
Just a thought but is probably why our DI engines runs so lean so as to prevent more carbon buildup as well as the hotter plugs.

Offline RufusMacblorf

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #3 on: September 23, 2010, 11:38:07 PM »
I've read about this fairly serious problem in the Audi RS4 and a couple of Porsche engines with DI.  I wondered if it might crop up in our car at some point.

Offline Sol Asylum

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #4 on: September 24, 2010, 12:49:06 AM »
Carbon is a by product of combustion.  Anytime that you burn a hydrocarbon fuel you are going to get carbon no matter what the fuel is be it gas, ethanol, Jack Daniels, whatever.  How much carbon is a function of how much fuel is burned and the chemical make up of that fuel.  The manor that the fuel is delivered to the combustion chamber will have no effect on how much carbon forms.

The only thing that I could see as being a carbon issue with DI is that the injector nozzle is in the cylinder and if carbon forms on the nozzle then it can affect the spray pattern of that nozzle.

Personally I wouldn't put much faith in what some Subaru fan has to say as the fact that their a Subaru fan makes me question their mental capabilities to begin with, but thats just me.
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Offline Carbon Sky

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #5 on: September 24, 2010, 01:26:29 AM »
As long as you run an appropriate tune for the way the car is driven, and always run premium fuel (which has more detergents) you should be just fine.  If you do get some build up after a while, run a little injector cleaner through the tank (I highly recommend either the AMSOIL P.I. or the Redline equivalent), and if you for some reason have build up before the combustion chamber, say a build up of oil from a leak or a PCV problem, run a little throttle body cleaner through the car.  I recommend the GM Cleenz.  It's specifically made for the job.  But these shouldn't be needed unless the car is running poorly, or there's something incompatible between driver and tune.

Offline Kuprito

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Offline snaponbob

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #7 on: September 24, 2010, 08:34:37 AM »
A tempest in a tea pot. Leaner mixture is because direct injection is more efficient and thus does not need to be as rich. Because the LNF Kappas soot up the tail pipes does not mean they soot up the engine. Example; when I ran the original plugs the tail pipes, O2 sensors, and spark plugs where sooty. When I changed to the supersede plugs, the tail pipe was sooty (but not quite as much) but the plugs and O2 sensors were clean (plugs very light, sensor nearly tan). The German cars are having oiling problems (very minor), and that is part of the issue. I scoped my engine a while ago, and at 25K miles, lots of different tunes, and power mods, nothing important is happening on the pistons. 
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Offline Brazen17

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #8 on: September 24, 2010, 09:41:11 AM »
A tempest in a tea pot. Leaner mixture is because direct injection is more efficient and thus does not need to be as rich. Because the LNF Kappas soot up the tail pipes does not mean they soot up the engine. Example; when I ran the original plugs the tail pipes, O2 sensors, and spark plugs where sooty. When I changed to the supersede plugs, the tail pipe was sooty (but not quite as much) but the plugs and O2 sensors were clean (plugs very light, sensor nearly tan). The German cars are having oiling problems (very minor), and that is part of the issue. I scoped my engine a while ago, and at 25K miles, lots of different tunes, and power mods, nothing important is happening on the pistons.  

That is very good news to hear.
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Offline gmtech16450yz

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #9 on: September 24, 2010, 01:21:03 PM »
The problem isn't the pistons, the problem is the valves that don't get cleaned by fuel going past them. I've seen LNF intake valves that look worse than a '65 Chrysler with 200k miles. The fuel you use won't have any effect on that, it's mostly from the oil coming from the PCV through the intake. Slow down that and it will greatly reduce the amount of carbon and oil deposits on the valves.


"The only thing that I could see as being a carbon issue with DI is that the injector nozzle is in the cylinder and if carbon forms on the nozzle then it can affect the spray pattern of that nozzle."

Absolutely true. I just changed all 4 injectors on an LNF for this very reason.

Offline MGar

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #10 on: September 24, 2010, 01:34:23 PM »
Cleaning the top end by running a type of cleaner (I use seafoam) through a vacuum port on the intake manifold before an oil change should help alleviate buildup.

I have been doing the solstice at every oil change, and it seems to idle with less felt fluctuation when cold.  The most recent time, I kept running the cleaner until it no longer created smoke, which, although took awhile, did finally occur.

The GTO I did at the same time, had 65K on the clock, and had never been top end cleaned before.  It created a single small puff of smoke, and that was it.  The solstice, however, created clouds with 24K on the clock.
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Offline Treeman

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #11 on: September 24, 2010, 03:09:26 PM »
it's mostly from the oil coming from the PCV through the intake. Slow down that and it will greatly reduce the amount of carbon and oil deposits on the valves.

Interesting given the PCV discussion we have been having.
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Offline chuckdoc

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #12 on: September 24, 2010, 03:34:59 PM »
To me, the most interesting thing about the PCV discussion was only two cars I know of had a PCV problem.

One was Grants (I forgot his forum name but he is never around any more)(how about some love, Grant).  His car was smoking and it was fixed by replacing the PCV.  This is not the PCV check valve, but the actual PCV valve which resides under the intake manifold and costs around 220 bucks to replace.  The other car with a suspected PCV valve issue was mine.  This turned out to not be the problem, but thats how I know the cost.

Mine was a turbo seal failure

The third car that was smoking was Lil Ndn and his was a BOV or wastegate problem.

So really  all the speculation about PCV has not been brought to fruition.
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Offline Treeman

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #13 on: September 24, 2010, 04:44:19 PM »
Ah...actually, I'm glad you summarized it all because I lost track of it all.
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Offline NormSky

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Offline Sol Asylum

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #15 on: September 24, 2010, 11:44:16 PM »
One was Grants (I forgot his forum name but he is never around any more)(how about some love, Grant).
Cheers? Chuck :cheers:
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Offline chuckdoc

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #16 on: September 25, 2010, 08:27:13 AM »
Yup, for people that did not know grant, his forum name was cheers. 

Lest you think SA was raising his glass for a toast!
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Offline Sol Asylum

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #17 on: September 26, 2010, 12:15:14 AM »
Cheers was/is a good forum member I would raise a glass for him.  He just needs to post more often.
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Offline MGar

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #18 on: September 27, 2010, 03:58:04 AM »
Scoped my valves today with a nice snap on snake camera with a light on the end.  Went in through the MAP sensor on the intake manifold.

25K on the odometer.

Granted, I have seafoamed the car through the intake manifold religiously before every oil change, and often using more than one bottle.
That said, the valves had virtually no signs of carbon buildup on them.  There was a minimal (spotty) amount around the edges of the valves, and that was it.
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Offline spider

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #19 on: September 27, 2010, 08:56:35 PM »
Are you putting it in before the throttlebody to clean it also if so, or not, where & using what to dispense the seafoam?

Offline MGar

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #20 on: September 28, 2010, 02:02:17 AM »
I remove the vacuum tube that connects between the manifold and the bypass valve solenoid.  I then put a longer hose on the vacuum nipple from the intake manifold, plug it with my finger, get the car started and preferably already have it warm.  Then I feed the tube into the bottle of seafoam.  I do not just drop the tube in, as it would suck in way too much.  You do not want to hydrolock the car.  After you have done it a couple of times, you just get a feel for it.

I basically modulate the tube so that it pulls it in, but am careful not to let it die, sometimes having someone else to bring the rev's up a bit helps.  Once I've had it suck down the majority of the bottle, I shut it off, and let it sit.  The whole process takes maybe 5 minutes, tops.  Of course, then plug everything back in the way it was.

Let it sit for 45 minutes to an hour, and then start.  It is usually pretty rough at first, and will likely smoke a lot while both giving it the cleaner, and after it has sat.  Eventually, it will stop smoking at idle, then give it a quick drive, and it will begin to smoke again.  Eventually it will stop smoking.  Take note, it produces a lot of smoke, so do not do this in a confined space.
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Offline tazz

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #21 on: September 28, 2010, 12:25:53 PM »
That's pretty much the same drill I use and it seems to work fine for me.
I do mine at a car wash that is not really used much and is way from others.  The first time people see it smokes like that they think the car is no fire it smokes that bad but a white choking smoke billows out.

Offline Graywolf

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Re: Does direct Injection cause severe cylinder carbon build up?
« Reply #22 on: September 28, 2010, 10:12:04 PM »
When I blew a piston last year I rebuilt the entire engine,No soot build up! Car had only 6000miles on it.
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