2003 Audi A4 1.8t with 87 octane

[Renner]

I thought under part throttle you could be lean (from stoich) and it's ok because you are not under full load? This would also cause a more complete burn of the fuel, i.e. better fuel economy. So most cars shot for above (numerically) stoich under part throttle?? Please correct me if I'm wrong, I do understand that you are just speaking in generalities too.

 

Stoichiometric is the ideal ratio where fuel is burned completely, going leaner then that does not cause a "more complete burn". Going leaner does increase fuel mileage of course. However, going leaner also increases NOx production. (NOx is how NO and NO2 are collectively referred to) NOx production is a very bad thing, so many car manufacturers don't target much leaner then 14.7:1.

 

And you were right, I was generalizing, every car has a different target for light load closed loop operation, 14.7 is just the largest average for cars on the road today. The newest cars, which are advertised as being "lean burn" engines, target in the ~16:1 range for closed loop. They have designed combustion chambers and catalytic convertors which can run in that lean of a range without increasing NOx production.

 

Wouldn’t know what that Audi’s target is without throwing a wideband on it, but it’s probably around the 14.7 range since Audi hasn’t done a major redesign of the 1.8T (allowing it to run that lean cleanly) for many years. Also keep in mind that common narrowband O2 sensors cannot reliably read AFR’s as lean as 16:1, so if your car has a traditional narrowband sensor in it, then it is most likely not running in the 16-17:1 range during closed loop operation.

[Renner]

Correct. Under vacuum cars will run about 16-17:1.

 

Not exactly, see my post above this one. Also, it's not as simple as saying "while under vacuum", since an engine is under vacuum while at idle, and most cars out there do not idle anywhere near the 16-17:1 range. An engine is also under vacuum while decelerating under load, and in that case it is much much leaner then 17:1.

[Nate1647545505]

I thought under part throttle you could be lean (from stoich) and it's ok because you are not under full load? This would also cause a more complete burn of the fuel, i.e. better fuel economy. So most cars shot for above (numerically) stoich under part throttle?? Please correct me if I'm wrong, I do understand that you are just speaking in generalities too.

 

Leaner you go, higher the NOx cout goes. Higher NOx goes, the enviroment gets pissed off, as does the EPA.

 

Most modern day factory ecus start the cross count at 450 - 500mv, which is "good enough" for stoich on narrowband, and adjust fueling depending on the trims of the loops. Rarely will a car ride at an exact ratio, but will always be changing as the electronics switch from rich to lean, lean to rich, yadda yadda. These variations from stoic are momentary, but the car does lean out some. So basically, they all shoot for "stoich" and any variation otuside of that are just the effects of the feedback loop.

[Nate1647545505]

Stoichiometric is the ideal ratio where fuel is burned completely, going leaner then that does not cause a "more complete burn". Going leaner does increase fuel mileage of course. However, going leaner also increases NOx production. (NOx is how NO and NO2 are collectively referred to) NOx production is a very bad thing, so many car manufacturers don't target much leaner then 14.7:1.

 

And you were right, I was generalizing, every car has a different target for light load closed loop operation, 14.7 is just the largest average for cars on the road today. The newest cars, which are advertised as being "lean burn" engines, target in the ~16:1 range for closed loop. They have designed combustion chambers and catalytic convertors which can run in that lean of a range without increasing NOx production.

 

Wouldn’t know what that Audi’s target is without throwing a wideband on it, but it’s probably around the 14.7 range since Audi hasn’t done a major redesign of the 1.8T (allowing it to run that lean cleanly) for many years. Also keep in mind that common narrowband O2 sensors cannot reliably read AFR’s as lean as 16:1, so if your car has a traditional narrowband sensor in it, then it is most likely not running in the 16-17:1 range during closed loop operation.

 

Nice thing about the Audi/VW setup is the Bosch LSU4 sensor, wideband from the factory, the way it should be in this day and age. Also, turbochargeres take thermal energy required by cats to operate, meaning they may run a tad leaner then NA guys.

[Nate1647545505]

Ahh crap, sorry Renner

[Drunkendubber]

Rigsby is just bitching cause he has to fill up his SUV for $50 some odd dollars and she is getting off easy with $20 fills. Quit ur bitching the car will be fine. The oil sludging is her biggest worry.

 

Kyle g.

[Kevin R.]

Way to go guys. If we didn't give him advice we could watch him punch her in the face.

[Mattsv8]

if that car has a wideband 02 good luck with the 87. i have a eclipse turbo 95. never put less than 93 in the tank and sometimes it gets a little 100 unleded yes cam 2 unleded is 100 octane not the 110 like most people think. but i can garentee you if that car sees about 8lbs boost with those stock pistons it will knock and it only has to miss one knock before hole in piston. i let my girl drive my car sometimes and i encurage her to drive it hard thats what the turbo is for i tell her not to shift before she sees at least 15lbs of boost. its great watching it funny. and she always puts 93 or better back in. you just got to train them!!!