Bad mpg?

[petethepug]

A new 5.3L V8 with a 10 SP, direct injection, DFM, running on adaptive cruse and 17.5 mpg on Reg fuel isn’t bad at all. Not sure what rims and tires you’re running or how hard a/c was working.

 

[blanchard7684]

I'm 5000 miles into a '24 suburban z71 with 5.3. I'm not focused on fuel mileage in general. However in testing difference between DFM and DFM disabled (L9) is noticed only about a 1 mpg difference with DFM engaged.

Where I drive it is alot of 75 mph highway, wind, and frequently a lot of hills.

I'm getting 17.5 mpg on average.

The window sticker values don't really reflect real world (75 mph speed limit) driving.

When I go 65 mph for appreciable amount of time I can easily meet and usually exceed the window sticker values.

 

[Marky Dissod]

... window sticker values don't really reflect real world (75MpH speed limit) driving.
When I go 65 mph for appreciable amount of time I can easily meet and usually exceed the window sticker values.

I find it interesting that, after decades of Corporate Average Fuel Economy testing,
leading from 3-speed to 10-speed transmissions and myriad technologies for improving MpGs,
'they' have never bothered to state a road speed range where a given vehicle gets near its best MpGs.
Whatever the 'city' MpG' cited by the Monroney sticker, it ain't easy to achieve that number.
It's a bit easier on the highway.
I'd prefer they say something like,
'if you want to get at least 2xMpG, keep it under 65MpH on the highway.'

 

[jfoj]

2024 Yukon Denali XL6.2l with upgraded 22" wheel package. About 2500 miles at this point in time.

Above 65-70 MPH MPG starts to tank. Also depends A LOT of how flat the roads are. Just pul up the Fuel Ecomony display that shows Instant MPG and you will see what the throttle does to fuel consumption.

From trip yesterday. About 30 miles was in town driving for the complete trip.

 

[onyx24]

2024 Yukon Denali XL with upgraded 22" wheel package. About 2500 miles at this point in time.

Above 65-70 MPH MPG starts to tank. Also depends A LOT of how flat the roads are. Just pul up the Fuel Ecomony display that shows Instant MPG and you will see what the throttle does to fuel consumption.

From trip yesterday. About 30 miles was in town driving for the complete trip.

Doesn't the Denali have the 6.2? I heard the 6.2 does better on the highway than the 5.3.

 

[jfoj]

Doesn't the Denali have the 6.2? I heard the 6.2 does better on the highway than the 5.3.

Yes, Denali has the 6.2l. Forgot to add that in, just included it in the post.

With the torque the 6.2l has along with the 10 speed transmission, it seems that the engine RPM's are pretty low at cruising and you do not need much throttle to keep speed up unless the road has more of an incline. Even with a slight incline if the transmisson drops from 10th to 9th gear, the engine does not wind up. This gets better fuel economy than my 2005 6.0l Denali XL. I used to dead criuse control in the 2005 when I hit and incline. The Torque Converter Clutch would disable and the trans would drop from 4th to 3rd gear and the engine RPM would double!!! Not this 2024 on the same route, I can leave the cruise on and the inclines are easily conquered without any drama.

Engine RPM was around 1500 RPM at 70 MPH in the picture I took. I think this is pretty typical, only driving the truck 2500 miles so far.

Not sure what the 5.2l RPM is at 70 on typical configurations, might be spinning a few more RPMs?

 

[onyx24]

Yes, Denali has the 6.2l. Forgot to add that in, just included it in the post.

With the torque the 6.2l has along with the 10 speed transmission, it seems that the engine RPM's are pretty low at cruising and you do not need much throttle to keep speed up unless the road has more of an incline. Even with a slight incline if the transmisson drops from 10th to 9th gear, the engine does not wind up. This gets better fuel economy than my 2005 6.0l Denali XL. I used to dead criuse control in the 2005 when I hit and incline. The Torque Converter Clutch would disable and the trans would drop from 4th to 3rd gear and the engine RPM would double!!! Not this 2024 on the same route, I can leave the cruise on and the inclines are easily conquered without any drama.

Engine RPM was around 1500 RPM at 70 MPH in the picture I took. I think this is pretty typical, only driving the truck 2500 miles so far.

Not sure what the 5.2l RPM is at 70 on typical configurations, might be spinning a few more RPMs?

I have a picture from the trip at 80mph it was 1750 rpm

And it was pretty flat roads... It seems to be getting better almost at 1k miles now

 

[blanchard7684]

It wouldn't surprise me if the 6.2 had a bit better mpg than the 5.3 on the highway. The larger displacement doesn't need as rich of A/F ratio to get enough power to climb small hills or overcome headwinds.

 

[Marky Dissod]

The larger displacement doesn't need as rich an Air/Fuel ratio to get enough power to climb small hills or overcome headwinds.

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.

 

[jfoj]

I forgot to add that this includes the Range AFM delete module in my vehicle. Not sure if this hurts fuel economy much, assume it does at least a small bit and with the Auto Stop/Start disabled, in town while sitting stopped in any traffic, stop lights or stop signs, the vehicle is Averaging EXACTLY 0 MPG!

Given the size and weight of the vehicle, while having a V8 I have no complaints for the MPG I have been seeing so far. If you want economy get the Diesel, but depending on the fuel prices in the area and the few Diesel related issues, you need to do your homework to decide if you really want a Diesel. I initial considered one until I started researching and really did not like the idea of the oil pump belt needing replacement around 100-125k miles, I think I saw at todays prices this could be a $3k job.

 

[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.