Direct Injection, Fuel Dilution, and Ring Sticking

[Ws6]

Originally Posted by bobdoo
Direct injection vaporizes fuel far more effectively than port injection, or carbs. That's one reason *why* auto mfrs use it.

I know my CX-5 dumps a lot of fuel at startup, to force the cat con to warm up faster. That contributes to fuel dilution.

The other big problem is the low-tension piston rings. They, again, contribute to MPG (in the fed testing regimen), but allow massive blow-by.

Improper break-in doesn't help. Those rings require high throttle bursts when the engine is new, to properly bed them to the cylinder wall.

My N/A CX5 did, too. My turbo CX5 seems much "better" tuned, though. The N/A CX5 ran PIG RICH for the first bit. Really tanked mpg and reeked like my old cammed up mustang GT with no cats.

 

[Ws6]

Originally Posted by BMWTurboDzl
Originally Posted by Propflux01
My questions are what actually causes the blow by, after all, diesels are in a sense direct injected and don't seem to have a problem, and what to do after the rings stick and you need to get them unstuck without tearing the engine down?


As I understand TGDI engines go through periods where they have to run rich in order to reduce combustion temps. This extra fuel with the addition of higher compression ratio causes some fuel to wash down into the crankcase. It's not "stuck rings" but possibly low tension rings which may exacerbate it.


Depending on the model some diesels have a little or a lot of fuel dilution when they're set up to inject extra fuel for DPF regen but outside of that scenario the big difference is that diesels use EGR not extra fuel to reduce combustion temps.


Mazda Sky-Active gas engines use EGR to reduce combustion temps.

Only the turbo model, which is ingenius in the use of EGR vs. fuel dumping. Helps real world MPG, even if EPA doesn't reflect it. My vehicle lifetime ownership is at 25.9mpg over 11K miles. EPA Rated 27mpg HIGHWAY.