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So common knowledge, DI engines have suffered from carbon buildup causing mayhem, power loss etc. at later miles (40k-60k depending).
Expensive, involved Seafoam, walnut blasting etc is the only real remedy for maintenance.
Even the 2014>on FA20DIT suffers from the issue. It was certainly an issue on my 2010 BMW’s N54 engine.

I heard a rumor that the newer FA24DIT is “better“ at this, but don’t exactly recall how/why.

Thoughts? Sorry if this has been discussed before.
 

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Here's Subaru's response when I asked...



"Thank you for contacting Subaru. I appreciate the opportunity to be of assistance.

Older direct injection systems that experienced carbon build up were so called “lean burn” systems. Unfortunately these systems suffered many times from uneven combustion due to variations in the fuel and air mixture throughout the combustion chamber. This created a mix of lean and rich conditions resulting in variations in combustion temperature and uneven burning of the gasoline. This uneven burning lead to the condensing of unburned and partially burned hydrocarbons which over time resulted in carbon buildup.

Subaru engineers understood this when they created our current direct injection system. They developed innovative yet simple systems to manage and control the combustion variations inside the combustion chamber. These include features such as specially shaped piston crowns, multi-patterned injection spray, and tumble generator valves. All of which promote the precise swirling and intermix of fuel and air under the variable conditions required across the full range of power requirements. When combined with very high fuel pressures and extremely short injection duration of the Subaru direct injection system, stoichiometric combustion is maintained across the combustion chamber resulting in very even and complete burning. As a result abnormal residue and carbon deposits are not created and engine performance and fuel economy are maximized.

Please note that our research does show that routine maintenance, per the warranty & maintenance booklet, is another important factor when avoiding any potential carbon buildup concerns."
 

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^^ Hmmm. Thanks. That is awesome news if it reflects reality.
Well, if anyone should be able to confirm the reality, I think it will be me, and my soon to be 50,000 miles of abusive driving. Now, the question is, where can I find to check out my valves at a price that won't break the bank...

...If I find a place, I'll let everyone know what they see.
 

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How does all that relate to API SN oil being formulated to help reduce deposits and low speed preignition in turbocharged direct injection gas engines, and API SN PLUS supposedly being even better? If the oil is helping, it's gotta be due to what gets into the intake via PCV right?

From Mobile 1: PI SN Plus is a supplemental oil category from the American Petroleum Institute (API). The oil formulations for API SN Plus are specifically designed to help prevent LSPI in TGDI (Turbocharged Gasoline Direct Injection) engines. API SN Plus represents an improvement on API SN, an oil category developed in 2010.

Also: API SN: Introduced in October 2010, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85.
 

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Well, if anyone should be able to confirm the reality, I think it will be me, and my soon to be 50,000 miles of abusive driving. Now, the question is, where can I find to check out my valves at a price that won't break the bank...

...If I find a place, I'll let everyone know what they see.
Boroscopes are ridiculously cheap these days!
 

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Boroscopes are ridiculously cheap these days!
I own two, but I do not have a warm garage to do it in, or the tools to properly disconnect intake and cork it back down properly. I used to. :(
 

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Here's Subaru's response when I asked...



"Thank you for contacting Subaru. I appreciate the opportunity to be of assistance.

Older direct injection systems that experienced carbon build up were so called “lean burn” systems. Unfortunately these systems suffered many times from uneven combustion due to variations in the fuel and air mixture throughout the combustion chamber. This created a mix of lean and rich conditions resulting in variations in combustion temperature and uneven burning of the gasoline. This uneven burning lead to the condensing of unburned and partially burned hydrocarbons which over time resulted in carbon buildup.

Subaru engineers understood this when they created our current direct injection system. They developed innovative yet simple systems to manage and control the combustion variations inside the combustion chamber. These include features such as specially shaped piston crowns, multi-patterned injection spray, and tumble generator valves. All of which promote the precise swirling and intermix of fuel and air under the variable conditions required across the full range of power requirements. When combined with very high fuel pressures and extremely short injection duration of the Subaru direct injection system, stoichiometric combustion is maintained across the combustion chamber resulting in very even and complete burning. As a result abnormal residue and carbon deposits are not created and engine performance and fuel economy are maximized.

Please note that our research does show that routine maintenance, per the warranty & maintenance booklet, is another important factor when avoiding any potential carbon buildup concerns."
When you say you contacted Subaru, can you be more specific re your source? Is there a link with this info?
 

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When you say you contacted Subaru, can you be more specific re your source? Is there a link with this info?
This same response from Subaru has been reported by multiple folks both here and in the MY20 Outback forum. I do not believe it's "online" that you can link to, but I could be wrong about that.
 

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When you say you contacted Subaru, can you be more specific re your source? Is there a link with this info?
In this case, I emailed them. Sometimes I speak directly with the Product Managers or other folks, but I generally try to remember to indicate that when I relay what they've said.

The answer above is a direct quote of their written response to my email.
 

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In this case, I emailed them. Sometimes I speak directly with the Product Managers or other folks, but I generally try to remember to indicate that when I relay what they've said.

The answer above is a direct quote of their written response to my email.
When you say email, are you talking about the Customer Support form you have to fill out, or do you have an actual email ID for SOA?
 

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When you say email, are you talking about the Customer Support form you have to fill out, or do you have an actual email ID for SOA?
I have both. I do not recall how or who I asked this particular question.
 

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I have both. I do not recall how or who I asked this particular question.
Don't get me wrong. I like the answer you got. I just don't want to repeat it to others (this is a big issue on other Subaru forums as well) unless it is credible, IE, not just some customer service or other non-expert's opinion. Sure would be nice if Subaru put this on their site somewhere.
 

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Don't get me wrong. I like the answer you got. I just don't want to repeat it to others (this is a big issue on other Subaru forums as well) unless it is credible, IE, not just some customer service or other non-expert's opinion. Sure would be nice if Subaru put this on their site somewhere.
It's an official answer that's actually in writing in various forms in the technical docs for the Ascent, as well as outlined in various other Subaru docs.

This isn't some support tech who doesn't understand the technology.

The various techniques and technologies are visible in the service manual, btw. It's all real and the answer is accurate.
 

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It's an official answer that's actually in writing in various forms in the technical docs for the Ascent, as well as outlined in various other Subaru docs.

This isn't some support tech who doesn't understand the technology.

The various techniques and technologies are visible in the service manual, btw. It's all real and the answer is accurate.
I believe you, and the response makes sense. Just would be nice to link to a doc or reference taken from an official Subaru source.
 

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I believe you, and the response makes sense. Just would be nice to link to a doc or reference taken from an official Subaru source.
I cannot link to internal docs. ;) :(

But, you can find most of it by paying for a three day account on STIS and digging through all the tech manuals for the car.
 

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I cannot link to internal docs. ;) :(
But, you can find most of it by paying for a three day account on STIS and digging through all the tech manuals for the car.
So would it be correct for me to say then that your quote from the email is from a tech manual on the Subaru site?
 

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So would it be correct for me to say then that your quote from the email is from a tech manual on the Subaru site?
No, but I suspect it's the same technical people who wrote the answer, which is why multiple people have been given the same answer.
 
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