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#1 (permalink) Old 02-07-2012, 05:57 AM
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Direct Fuel Injection

The March 2012 issue of Road & Track had an informative explanation of direct fuel injection. Here it is:
"Fuel injection covers a broad range of methods of squirting fuel into an engine, and direct fuel injection is just one of those methods. Thus, an engine can be both fuel injected and direct fuel injected, but not all fuel-injected engines use direct injection.

What direct signifies is a system that sprays fuel directly into an engine's combustion chamber. This is significantly different than multiport fuel injection found on the overwhelming majority of automobile engines in the last 20 years.

Multiport fuel injection places a fuel injector just upstream from the intake valve. This allows a relatively low fuel pressure- say 30 to 60 psi- that in turn allows relatively simple and thus inexpensive pumps and injectors.

Direct fuel injection must overcome the high pressures inside the combustion chamber and thus operates at approximately 2,500 psi. This requires more expensive pumps and injectors, higher-strength plumbing and sound deadening, so direct fuel injection is considerably more expensive, typically costing several hundred dollars more per engine than multiport injection. What you get for the extra money is a finer spray of smaller fuel droplets and increased cylinder cooling, both of which yield greater engine efficiency.

We're in the middle of the switch to direct fuel injection, so you'll find thenewest engines use it and not necessarily the most powerful, expensive, or sportiest powerplants."

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#2 (permalink) Old 02-07-2012, 04:20 PM
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I believe those skyactiv mazda engines are using direct injection to help with predetonation (no fuel to predetonate till its needed) since they have such high compression. Interesting stuff.

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#3 (permalink) Old 03-01-2012, 01:51 PM
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A while back I mentioned that the Ford 5.0 has heads already prepped with the boss reliefs already in place for a possible future upgrade to DI and nearly got laugh of of this site when I mentioned that the 5.0 would achieve a substantial horsepower increase as a result.

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Former 2010 TorRed SRT8 6spd owner
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#4 (permalink) Old 08-22-2012, 12:34 PM
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I had an '07 Audi Q7 and an '08 Audi RS4 both with FSI engines. When it was new they made good power but over time the engines started to lose performance. From what I understand it was because of the direct injection technology. Because fuel is sprayed directly into the chambers it no longer washes over the valves. The valves get coked up with carbon very quickly with all Audi FSI engines and is a problem with all other DI engines as well.

Audi at the time was not admitting that this was a problem and wasn't honoring warranty claims. The customer would have to pay to have the intake removed and point at the carbon build up in order to get the intake and valves cleaned up under warranty. They used some sort of device with ground up hazelnut shells to clean up all the carbon.

I've since sold both of my Audis.
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#5 (permalink) Old 08-22-2012, 12:55 PM
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The new v6 mustang and v6 camaro engines are direct injected and as a result get sweet mpg and power. Due to the fine atomization of the fuel, these engines can be run leaner than typical fuel injection and not have heat issues associated with lean runs. Also, I have heard that the combustion chamber of a direct injected motor stays clean due to the extreme lean run and total burn of almost all the fuel. I wish Dodge would adopt it.

I cannot speak for the carbon in the intake valve. How does oil and fuel get there to build up? Why do the valves need to be removed to clean them? Can the intake not be removed and then blast the valves with walnut shells?
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#6 (permalink) Old 08-22-2012, 01:04 PM
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Quote:
Originally Posted by rscarawa View Post
The new v6 mustang and v6 camaro engines are direct injected and as a result get sweet mpg and power. Due to the fine atomization of the fuel, these engines can be run leaner than typical fuel injection and not have heat issues associated with lean runs. Also, I have heard that the combustion chamber of a direct injected motor stays clean due to the extreme lean run and total burn of almost all the fuel. I wish Dodge would adopt it.

I cannot speak for the carbon in the intake valve. How does oil and fuel get there to build up? Why do the valves need to be removed to clean them? Can the intake not be removed and then blast the valves with walnut shells?
It's a well documented problem:

quattroworld.com Forums: Unofficial RS4 Carbon Buildup Log

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#7 (permalink) Old 08-22-2012, 02:43 PM
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I know oil builds up on my truck's throttlebody too. How does oil get in there?

Is this a problem on all direct injection motors or just certain brands?
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#8 (permalink) Old 08-22-2012, 02:53 PM
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Check this article as it will better explain it:

Direct Injection Fouls Some Early Adopters - AutoObserver

It's a problem with all DI engines from all makes, MB, Cadillac, Audi, VW, Ford etc.

What's amazing is in the article VW admits that carbon buildup is a problem with the technology but chose to produce FSI engines anyway, as has everyone else. DI is great in the beginning but what they don't tell you is that you'll have to get your intake and valves cleaned every 30K+ miles.
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#9 (permalink) Old 08-22-2012, 03:12 PM
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Quote:
Originally Posted by Randy M View Post
Check this article as it will better explain it:

Direct Injection Fouls Some Early Adopters - AutoObserver

It's a problem with all DI engines from all makes, MB, Cadillac, Audi, VW, Ford etc.

What's amazing is in the article VW admits that carbon buildup is a problem with the technology but chose to produce FSI engines anyway, as has everyone else. DI is great in the beginning but what they don't tell you is that you'll have to get your intake and valves cleaned every 30K+ miles.
Good article. It says that GM has not had this problem yet.
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#10 (permalink) Old 11-24-2012, 10:55 PM
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Quote:
Originally Posted by Randy M View Post
I had an '07 Audi Q7 and an '08 Audi RS4 both with FSI engines. When it was new they made good power but over time the engines started to lose performance. From what I understand it was because of the direct injection technology. Because fuel is sprayed directly into the chambers it no longer washes over the valves. The valves get coked up with carbon very quickly with all Audi FSI engines and is a problem with all other DI engines as well.

Audi at the time was not admitting that this was a problem and wasn't honoring warranty claims. The customer would have to pay to have the intake removed and point at the carbon build up in order to get the intake and valves cleaned up under warranty. They used some sort of device with ground up hazelnut shells to clean up all the carbon.

I've since sold both of my Audis.
Hazel nuss, auf!
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