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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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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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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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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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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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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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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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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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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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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!
Motor Nutella......
 

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i know this is a old post but DI is superior for fuel milage,emissions as well as power. and yes you do get oil build up on the valves as well as carbon. im a diesel mechanic for 25 yrs and have seen the evolution of DI. from its simplest form to todays systems its a beast. but with that said we still have power loss due to carbon/oil build up on valves.. till we can figure out a way to do away with lubricating the valve stem or removing valve completely this will always be a issue. it just needs to be a common practice to do a motorvac or equivalent procedure to take care of the issue.
 

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i know this is a old post but DI is superior for fuel milage,emissions as well as power. and yes you do get oil build up on the valves as well as carbon. im a diesel mechanic for 25 yrs and have seen the evolution of DI. from its simplest form to todays systems its a beast. but with that said we still have power loss due to carbon/oil build up on valves.. till we can figure out a way to do away with lubricating the valve stem or removing valve completely this will always be a issue. it just needs to be a common practice to do a motorvac or equivalent procedure to take care of the issue.
From what I am reading, not all DI has carbon buildup issues on the valves. For instance, I have heard that GM's version does not. Seems like a problem more with the VW/Audi design than a DI design issue.
 

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Isn't this what a Catch Can helps to reduce, these deposits, as quoted from the above article?: "DI engines are prone to forming oily deposits on the intake valves, unlike in port fuel-injected engines, where a constant spray of fuel into the port allows any deposits to wash away." The PCV (Postive Crankcase Ventilation) Valve sends these crankcase vapors, which are caused by piston ring blowby and oil vapors (if I remember correctly), into the air intake and travels into the combustion chamber to be burned by the combustion of fuel. As these oily vapors travel across the valve, these are what contribute to these deposits, correct? Maybe not causing 100% of the deposits, but a major portion I would assume, in any PCV equipped engine.
I am in no way an engine expert, but from what I do know from working around the garage on various combustion engines, anything that helps reduce the oil vapors from traveling into the intake runners will help reduce these deposits on the intake valves.

Any thoughts on this? Why not add a catch can system on a DI engine to help reduce these deposits, or is their a mandate that a PCV be used to keep these fumes from being sent into the atmosphere like they were before PCV valves? I know from reading up on Catch Cans, the auto makers wouldn't want to add a Catch Can and require it's emptying. Too many people would forget or neglect to perform this needed maintenance.

EDIT: If I had read the entire article first, I would've found this: "All modern gasoline engines return some crankcase and exhaust gases back through the intake manifold in order to help control emissions, but, according to Chick, some exhaust-gas recirculation designs are “dirtier" than others. Some, he said, are less-effective at preventing the passage of tiny bits of oil, carbon and other particulates that eventually get baked onto the intake ports and valves."
 

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GM still has a major problem with the DI cars. GM says they don't but the mechanics I know see major carbon build up still to this day on the DI GM stuff. A catch can will help but its only a matter of time before there is carbon build up again. A lot more going on other than just the intake charge carrying the oil in.

I will NOT buy a car with DI until its proven that there is no more carbon build up problem. Right not its no where near fixed.
 

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Direct injection is awesome, for like a year. Just did a carbon cleaning on a VW 2.0L FSI engine with 40k miles on it. Im a mech. at VW and we do those on the regular. Got a used Cadillac 3.6 DI in that needs a carbon cleaning too. Its a big issue with any direct inject car really. And is it worth it? Chrysler is making 300hp with a v6 that gets 30mpg...with MPI. That Cadillac is also a 3.6. Same power (i think, nothing greatly different) Gets the same, if not less gas mileage and its direct injected...more stuff to go wrong if you ask me. The injectors are a PITA to service also. Personally, from a mechanics POV its not worth the effort. The little Direct Injection badges look and sound cool though. On the plus side, Audi's new FSI motor contains DI and MPI for both efficiency and valve cleaning lol. Talk about over engineered.
 

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Alot of the timing we see pulled in our is from the oil/carbon build on the pistons.
I have 5000miles on the new motor, catch can always been on it.
In 5000 miles the oil the CC misses, is on my piston tops right now. Causing ST timing to be pulled.
This is why I dont vent into my motor anymore. I vent to open air and use a electric vaccum pump. Look for a thread write up soon on this issue of carbon and decarbon the motor and one for the vac pump system I use..
FlatTop
 

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Alot of the timing we see pulled in our is from the oil/carbon build on the pistons.
I have 5000miles on the new motor, catch can always been on it.
In 5000 miles the oil the CC misses, is on my piston tops right now. Causing ST timing to be pulled.
This is why I dont vent into my motor anymore. I vent to open air and use a electric vaccum pump. Look for a thread write up soon on this issue of carbon and decarbon the motor and one for the vac pump system I use..
FlatTop
Very interesting cant wait to see your post/write up on this.
 

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The only experience I have with DFI (if you want to call it that) is with my wife's '13 Kia Optima I bought last year. It has a tiny 1.8 liter turbo and makes 276 HP!! Gotta be honest, I'm truly impressed with that little engine. A couple guys with a chain and a 2x4 could yank that engine out! :yes nod:

At least I got the lifetime warranty in case it does decide to "carbon up" down the road. So far so good though, but it only has a bit over 14K on it.
 

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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?
It is due to intake air pulse reversion. It is a feature of any naturally aspirated four stroke engine that uses old tech intake and exhaust valves. The valve coking problem on DI engines has not been resolved yet to my knowledge.

The valve coking is one problem where I think a oil catch can could possibly help, however valve face and seat life will be shortened.

Sometimes new technology brings new problems.
 
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