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My Fuel Economy


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ok, so I've started a quest for fuel economy in my truck

My truck is a 2009 Sierra 1500 CCSB SLT w/ 5.3 AFM, 3.42 87 octane (10% ethanol).

 

I drive ~300 miles per weekend during deer season so I have plenty of testing on the same roads.

I have tweaked the tune a little bit (with HP Tuners) to keep it in 4 cyl mode longer.

 

I have noticed that on flat land I can keep it in 4 cyl mode more than 8 cyl. mode IF I keep my speeds to 55 mph or less.

@ 65 mph I get ~18-18.5 mpg

@ 55 mph I get 23 mpg

@ 50 mph I get ~28 mpg

 

These are figures calculated from the DIC or course because I am not driving the entire trip at the same speed because of varying highway speeds.

 

The key to good fuel economy being able to keep the motor in 4 cyl mode.

The problem with that is you are driving essentially a "brick in the wind".

Of course it takes a certain amount of power to propel X amount of mass @ Y speed.

 

With a few tweaks to the tune I have made the truck have a little more tolerance to stay enter and stay in 4 cyl mode. Speed is the killer of fuel economy, I tried keeping up with a friend leaving the camp this weekend and @ 75 mph my fuel economy dropped to the 16.5 mpg range.

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Same results apply to the other motors as well. I found with my previous truck, If I could keep it 65mph or below, I could achieve 19mpg pretty easy on a trip. Thats using cruise and setting it at 64mph.

 

The new truck, I've not been on a trip yet with it to check, but so far my best has been 16.5mpg and thats running 65mph about 35 miles one way to relatives.

 

Your mileage is awesome though, but driving below the posted speed limit sucks... :thumbs:

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damn 28mpg? thats awesome. what did you do to help it stay in 4cyl?

I have touted the benefits of a true CUSTOM tune many times on this forum and it has fallen on deaf ears. I'm sure Black Bear can tune just fine, but even the best tuner will admit that their work can be better if they do it in person and spend more time with it, not just an hour or less. By tuning myself I can make logs while doing my daily driving and re-tune every day (or every 15 minutes) if I so desire/ find an adjustment I'd like to make.

 

I have been tuning using HP Tuners for the past 5 years on various trucks from radical heavily cammed / motor swapped trucks to essentially stock. When I bought my current truck I knew I would probably keep it mild, but I was intrigued by the AFM. After reviewing the tune and researching a little I found that I could take GM's parameters and adjust them a "little here" and a "little there" and make the truck more tolerant of the parameters that trigger the change between engine modes. I can now ride *on flat land* for several minutes at a time easily at certain speeds without leaving 4 cyl. mode.

 

one key factor is to keep it at a steady engine load, this doesn't necessarily mean use cruise control or that the speed has to be steady - a big factor of what makes the engine switch back to 8 cyl mode is the pressure changes within the intake manifold (where the main factor on determining engine load comes from) and you are always walking a fine line to keep over 5,000 lbs of steel moving in 4 cyl.

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I'm not doubting your numbers or even the AFM business. BUT I'd be curious to see the same tests run with AFM off. :thumbs:
I'm curious too... I just haven't gotten around to that stage of testing as of just yet. Next stage of testing involves using 89 octane (which in my area has no ethanol, and of course I will be making proper adjustments in the tuning for it). I can say that it appears that fuel economy improves slightly as it transitions from V8 to V4, but I can't say for sure and the difference is only a couple mpg, but a couple mpg is better than nothing as long as the system doesn't give me any problems.

 

How can you drive the truck so slow? Mine always wants to run around the 65 mph mark.

it's not easy, but my wallet keeps kicking my but every time I try to speed up :lurk:

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I'm not doubting your numbers or even the AFM business. BUT I'd be curious to see the same tests run with AFM off. :lurk:
I'm curious too... I just haven't gotten around to that stage of testing as of just yet. Next stage of testing involves using 89 octane (which in my area has no ethanol, and of course I will be making proper adjustments in the tuning for it). I can say that it appears that fuel economy improves slightly as it transitions from V8 to V4, but I can't say for sure and the difference is only a couple mpg, but a couple mpg is better than nothing as long as the system doesn't give me any problems.

 

 

Well keep us posted! :thumbs:

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I don't have a tune but I can keep my truck in V4 depending on the day up until around 50mph. Unfortunately the thing I hate about V4 is as soon as it kicks in the truck starts slowing down so I have to slowly press harder on the peddle to make it maintain its speed while staying in V4. Doesn't matter what speed I am going that seems to happen all the way down to like 30mph, at 30mph it can hold in V4 lol. I really wish they would let me manually put it in V4 mode, that way I could judge myself when to turn it on and off (or let it do auto)

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I'm not doubting your numbers or even the AFM business. BUT I'd be curious to see the same tests run with AFM off. :lol:
I'm curious too... I just haven't gotten around to that stage of testing as of just yet. Next stage of testing involves using 89 octane (which in my area has no ethanol, and of course I will be making proper adjustments in the tuning for it). I can say that it appears that fuel economy improves slightly as it transitions from V8 to V4, but I can't say for sure and the difference is only a couple mpg, but a couple mpg is better than nothing as long as the system doesn't give me any problems.

 

How can you drive the truck so slow? Mine always wants to run around the 65 mph mark.

it's not easy, but my wallet keeps kicking my but every time I try to speed up :D

 

 

 

I think its time for a new wallet.

 

I have tried driving my 01 silverado slower. But it doesn't matter how fast I am going or if I am pulling a trailer, I always average 16 to 17 mpg.

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How can you drive the truck so slow? Mine always wants to run around the 65 mph mark.

 

 

I have spent alot of time watching the mpg display and some results are very interesting. I try to watch how climbing a hill "bogged down" holding a gear compares to allowing a downshift during the climb. I have not seen anything conclusive that makes me think it matters either way.

 

 

One thing that is noticeable is each gear naturally has a speed range where it is most effective. For example a 3% grade at 75mph will not initiate a down shift to 5th but a steady 60mph on the same hill will cause a downshift. In other words the deciding factor of which gear you can climb the hill in is the torque curve of the engine. I know this is all common sense. But this also plays a key roll in fuel mileage. You will bog a 6spd trying to hold 50mph on flat ground therefore requiring more throttle. But you can run 60mph in 6th all day with minimal throttle. But then the laws of physics takes over and the rolling resistance, wind resistance, and slightly higher rpm's negate any gains. Speed has a huge impact on fuel consumption but too slow can make it suffer as well IMO.

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