Bad mpg?

[blanchard7684]

This statement no longer applies, now that O2 sensors force a 14.7 AFR whenever the driver presses down on the go-pedal.
(When lifting off, it COULD go as lean as 15.0 in rare situations,
and if load is high enough, it'll go into Power Enrichment to cool the combustion chamber and keep NOx low.)

With a 10speed, I'd not be surprised if a 6.2L would get equal or better MpGs than a 5.3L, under 70MpH at least.

How do O2 sensors force an A/F ratio?

 

[2024 White Tahoe]

Brand new vehicles typically run richer for a predetermined number of miles to aid in the break-in process. There are MANY components that are all finding their groove so to say, give it until 5k and see where you're at.

Also, cruise control will never give as good MPG as a well trained right foot in my experience over many years and miles of driving long distances.

How did you determine that, “Brand new vehicles typically run richer for a predetermined number of miles to aid in the break-in process”?

 

[Marky Dissod]

How do O2 sensors force an Air/Fuel ratio?

It's what Closed Loop does, it's what O2 sensors are for.
ecm has predictive maths tables that help it make very close guesses as to how much fuel to add
for how much air has been measured, split second by split second.
These guesses are never quite as correct as the automaker or the environmentalists would prefer, so,
once the engine is warm enough, O2 sensors refine those guesses by reacting to pre-cat exhaust gas composition.
Even O2 sensors are not quite perfect, but if the goal is between 14.667 and 14.68,
O2 sensor readings help refine the guesses so that the credibly repeatable goal at nearly every operating condition
when the driver is using the go-pedal normally is between 14.6 & 14.8.
If the vehicle is decelerating / coasting while the driver is 'lifting', the Air/Fuel ratio will likely be 14.7-14.8.
If the vehicle is accelerating 'normally', 14.6-14.7.

Overarching goals are to keep the catalytic converters alive as long as possible (why oil has less zinc today),
and to reduce NOx as much as possible, by keeping Air/Fuel ratios very close to 14.7 whenever reasonably possible.

 

[Doubeleive]

they all buy and sell and trade credits, no real incentive to redesign the internal combustion engine.
they just got caught like Volkswagen and stellantis and are paying a 146 million dollar fine (paid/loss of credits)
that is a literal slap on the hand for such a large company
all of our 2012-2018 pickups and suv's emit 10% more emissions than what have been reported to the epa

 

[blanchard7684]

It's what Closed Loop does, it's what O2 sensors are for.
ecm has predictive maths tables that help it make very close guesses as to how much fuel to add
for how much air has been measured, split second by split second.
These guesses are never quite as correct as the automaker or the environmentalists would prefer, so,
once the engine is warm enough, O2 sensors refine those guesses by reacting to pre-cat exhaust gas composition.
Even O2 sensors are not quite perfect, but if the goal is between 14.667 and 14.68,
O2 sensor readings help refine the guesses so that the credibly repeatable goal at nearly every operating condition
when the driver is using the go-pedal normally is between 14.6 & 14.8.
If the vehicle is decelerating / coasting while the driver is 'lifting', the Air/Fuel ratio will likely be 14.7-14.8.
If the vehicle is accelerating 'normally', 14.6-14.7.

Overarching goals are to keep the catalytic converters alive as long as possible (why oil has less zinc today),
and to reduce NOx as much as possible, by keeping Air/Fuel ratios very close to 14.7 whenever reasonably possible.

If the o2 sensor is only sensing the contents of exhaust how can it “force” a specific af ratio?

 

[Antonm]

If the o2 sensor is only sensing the contents of exhaust how can it “force” a specific af ratio?

Are you trolling / trying to argue semantics ,,,or is this a legit question?

Because it's kind of basic 101 level stuff he's talking about, and most people that know what an air fuel ratio is, also know what Marky Dissod is talking about.

Sure arguments could be made that its not the sensor itself controlling the air fuel ratio, but the input the sensor gives the PCM but really, arguing over semantics like that is like Range Technology arguing that zero cylinder is not part of DFM, so their device technically disables DFM even though it still allows the lifters to collapse on every drive.
...

 

[blanchard7684]

Are you trolling / trying to argue semantics ,,,or is this a legit question?

Because it's kind of basic 101 level stuff he's talking about, and most people that know what an air fuel ratio is, also know what Marky Dissod is talking about.

Sure arguments could be made that its not the sensor itself controlling the air fuel ratio, but the input the sensor gives the PCM but really, arguing over semantics like that is like Range Technology arguing that zero cylinder is not part of DFM, so their device technically disables DFM even though it still allows the lifters to collapse on every drive.
...

It is a legit question for someone who thinks that the oxygen sensor sets the af ratio, or “forces” it.

Hardly semantic issue when confusing inputs and outputs in feedback control loops.

As you said 101 stuff here so it should be easy to explain.

 

[Antonm]

It is a legit question for someone who thinks that the oxygen sensor sets the af ratio, or “forces” it.

Hardly semantic issue when confusing inputs and outputs in feedback control loops.

As you said 101 stuff here so it should be easy to explain.

No, IMHO you're just trolling and trying to be a jerk with technicality . You knew what he meant, and so did everyone else that read it.
...

 

[B-train]

How did you determine that, “Brand new vehicles typically run richer for a predetermined number of miles to aid in the break-in process”?

I used to do engine development and that was a common practice. I can't say for certain that all manufacturers do it, but it's a way to ease the new motors into life because you can't be certain people will treat a new engine properly right off the bat.

 

[Marky Dissod]

How O2 Sensors Work
O2 sensors work like mini generators, producing their own voltage as they get hot.
Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb.
The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.

The outside of the bulb is exposed to hot exhaust gases while the inside of the bulb is vented internally through the sensor body to the outside atmosphere.
Older style O2 sensors actually have small holes in the body shell so air can enter the sensor.
Newer style O2 sensors "breathe" through their wire connectors and have no vent holes.
Hard to believe, but the tiny space between the insulation and wire provides enough room for air to seep into the sensor
(this is why grease should never be used on O2 sensor connectors, because it can block air flow).
Venting the sensor through the wires reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.
The difference in O2 levels between exhaust and outside air in the sensor causes piezoelectrically generated voltage to flow through the ceramic bulb.
The greater the difference, the higher the voltage reading.

O2 sensors typically generate up to about 0.9 Volts when the fuel mixture is rich / when there is little unburned O2 in the exhaust.
When the mixture is lean, the O2 sensor's output voltage drops down to about 0.1 Volts.
When the Air/Fuel Ratio is stoichiometric (about 14.7:1 for pure petrol), the O2 sensor reads about 0.45 volts.

When the ecm gets a rich signal (high voltage) from the O2 sensor, it enleans the fuel mixture in the hope of reducing the sensor's reading.
When the ecm gets a lean signal (low voltage) from the O2 sensor, it enriches the fuel mixture in the hope of raising the sensor's reading.

O2 sensors must be hot enough to generate voltage, so many O2 sensors have a small heating element inside to help them hit operating temperature sooner.
The heating element can also prevent the sensor from cooling off too much during prolonged idle or DFCO, which would cause the system to revert to open loop.

Heated O2 sensors are used mostly in newer vehicles and typically have 3 or 4 wires. Older single wire O2 sensors lack heaters.

This ain't no 101 schidt, and it's nothing to do with what I 'think'.
Neither is the fact that some ecms allow tuners to adjust the 'voltage swingpoint', and a few even let tuners adjust the outer bounds as well.