Are DFI engines unreliable?
02-03-2016, 10:48 PM
#1
Nordschleife Master
Thread Starter
Are DFI engines unreliable?
In case you are not aware,in a direct injection engine,the injector sprays directly into the combustion chamber,thus on top of the piston. Checking Porsche's DFI design,I was a bit hopeful that these engines will not suffer VW and Audi's faith,but I might have been mistaking about that.
I am not looking forward seeing what happens in higher miles engines...
This is a post I've made about DFI engines in a different thread :
EDIT : Photo removed. Sorry.
I am not looking forward seeing what happens in higher miles engines...
This is a post I've made about DFI engines in a different thread :
Another point I need to make : I don't like DFI engines. They make more power and they're more efficient but I hate them!
If you are a technical person that understands in detail the workings of an engine,you are fairly skilled at working on an engine and most importantly YOU CARE ABOUT RELIABILITY,you will not like a DFI engine. They are very complex,very very expensive to maintain and fragile IMO. The injectors are exposed to extreme heat causing them to fail,coils fail due to heat,spark plugs wear at a ridiculous rate etc. The PCV systems in these are complete garbage,they are dumping oil vapors on the back of the valves with no way of cleaning them short of pulling the head. It is the reason why most manufacturers are adding back port injection,either in the form of spraying gas occasionally on demand,or spraying water,which forms a fine mist that turns into vapors from heat and cleans the valves.
Direct injection combined with Port injection is the only way moving forward IMO.
If you are a technical person that understands in detail the workings of an engine,you are fairly skilled at working on an engine and most importantly YOU CARE ABOUT RELIABILITY,you will not like a DFI engine. They are very complex,very very expensive to maintain and fragile IMO. The injectors are exposed to extreme heat causing them to fail,coils fail due to heat,spark plugs wear at a ridiculous rate etc. The PCV systems in these are complete garbage,they are dumping oil vapors on the back of the valves with no way of cleaning them short of pulling the head. It is the reason why most manufacturers are adding back port injection,either in the form of spraying gas occasionally on demand,or spraying water,which forms a fine mist that turns into vapors from heat and cleans the valves.
Direct injection combined with Port injection is the only way moving forward IMO.
EDIT : Photo removed. Sorry.
Last edited by neanicu; 02-04-2016 at 08:33 AM.
02-03-2016, 10:50 PM
#2
Rennlist Member
02-03-2016, 11:01 PM
#3
Nordschleife Master
Thread Starter
This is why I was a bit more hopeful about Porsche's DFI design. Notice in the pic that it seems there's a chance fuel gets a bit on the intake valve,but I don't know what happens in reality...
Last edited by neanicu; 08-31-2016 at 09:02 AM.
02-03-2016, 11:03 PM
#4
I could use a little edumacation here, as a non-engineer, non-technical noob. How would, say, a non-DFI Mezger engine look at similar number of miles? Does this degree of carbon buildup cause problems? If so, what are they? Thanks in advance.
02-03-2016, 11:13 PM
#6
My understanding is that one of the main advantages of DFI is that the fuel can be injected later during compression stroke and not the intake stroke. So the fuel will not spray while the intake valve is open, correct? That pic seems inaccurate.
Trending Topics
02-03-2016, 11:16 PM
#8
Nordschleife Master
Thread Starter
I don't remember seeing that amount of carbon buildup in port injection engines at 100K miles,let alone at 2200. I do not believe that amount of carbon on top of the piston can cause trouble,but I am afraid it's quite a lot more on the back of the valves,where fuel does not reach and clean anymore. Looking at Porsche's DFI design,it would seem that the exhaust valves would be most affected.
Sure,if the valves do not open and close properly because of carbon buildup,it can cause misfires in the engine. AFAIK,the misfires manifest especially on cold startup.
02-03-2016, 11:19 PM
#10
Nordschleife Master
Thread Starter
I am not trolling. I own this engine and I am just as concerned. Pay attention,you might learn something. You are certainly not bringing anything valuable here. Besides the tools thread,I have not seen any useful posts from you.
02-03-2016, 11:27 PM
#11
Ok, that explanation is helpful. Thanks! I guess we'll have to wait and see if we start seeing cars coming in with misfires of this sort. I haven't heard of this being a problem in particular, in either the current 9A1 or the post-2009 Mezger DFI engines. (I don't want to make this a Mezger vs 9A1 debate either!!! That dead horse has been flogged enough already.)
02-03-2016, 11:33 PM
#12
Drifting
That's a bit of a reckless headline to a thread...
This has been an accusation of DFI engines for awhile now. It's not quite that black and white. Here is a nice explanation:
http://www.autoguide.com/auto-news/2...-engines-.html
Mj
This has been an accusation of DFI engines for awhile now. It's not quite that black and white. Here is a nice explanation:
http://www.autoguide.com/auto-news/2...-engines-.html
Mj
02-03-2016, 11:36 PM
#13
Nordschleife Master
Thread Starter
I believe the pic is from a Porsche technical brochure and it represents the boxer DFI engine,but I can't be certain if the spray of gasoline actually hits the intake valve,as represented in the pic.
02-03-2016, 11:38 PM
#14
Rennlist Member
Good news is I haven't heard of any 9A1 engines expiring due to this issue. Which is not to say it won't happen. For those of us with E or F engines it might just be something we taker care when we replace our rockers on the 50,001 mi. major service.
02-03-2016, 11:40 PM
#15
Rennlist Member
Good pic here of a 997.2 DFI motor (9A1 design):
http://www.6speedonline.com/forums/9...-build-up.html