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Tuning Afm Out Hurt Gas Mileage?


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#1 rat454

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Posted 22 March 2011 - 12:57 PM

Just put a dynomax cat back system on my truck this weekend. I love the sound until V4 kicks in. One option to cure the drone is to tune the AFM out with a black bear tune or the like. Does anyone have any feedback on whether this hurt their gas mileage dramatically. Right now my truck gets 17-18 in town and 20-21 on the highway.
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#2 old-chevy-dude

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Posted 22 March 2011 - 01:09 PM

AFM is rated for a 9% - 25% increase in MPG..


so tuning it out you will lose 1 - 5 MPG depending on driving habits and conditions.

#3 Sir Dan

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Posted 22 March 2011 - 01:11 PM

I've noticed very, very little drop in mileage. Probably amounts to .2 mpg or less and in my opinion it's well worth it to get rid of that awful lawn tractor sound. Also much smoother on the highway without all the jumping back and forth.
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#4 Stevens11

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Posted 22 March 2011 - 01:12 PM

For me.. and my previous Vmax 6.0L, I ran a 2 week test with it on, and with it turned off using my diablo tuner. I saw no difference in mileage either way so I turned it off. I drove approx 300 miles each week and saw no difference. :)

Guys with the 5.3L however have reported results. So it's a toss up.

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#5 pm26

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Posted 22 March 2011 - 01:33 PM

25% increase in mileage? :)

#6 pm26

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Posted 22 March 2011 - 01:34 PM

I've noticed very, very little drop in mileage. Probably amounts to .2 mpg or less and in my opinion it's well worth it to get rid of that awful lawn tractor sound. Also much smoother on the highway without all the jumping back and forth.


What you mean smoother? Isn't the system switching undetectable?

#7 txab

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Posted 22 March 2011 - 01:55 PM

I've noticed very, very little drop in mileage. Probably amounts to .2 mpg or less and in my opinion it's well worth it to get rid of that awful lawn tractor sound. Also much smoother on the highway without all the jumping back and forth.


What you mean smoother? Isn't the system switching undetectable?

Nope. Not on all vehicles

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#8 Rymanh24

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Posted 22 March 2011 - 02:54 PM

If I could add my .2 cents. I believe if you have great driving habits and not a lead foot, yes AFM can actually help you out and give you better gas mileage.

I have actually gotten so good at feathering the pedal I can keep a constant speed between 28 mph and about 45 mph with just AFM or V4 mode. This feathering of the pedal has saved me lots of gas and money. I can get about 2 weeks out of my tank when I feather the pedal, and thats with my normal driving mileage of around 12,000 miles a year.

However when I gas it a lot it only last me about a week, so AFM in my case has been very helpful.

#9 music

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Posted 22 March 2011 - 03:51 PM

My feeling (no data) is that AFM works pretty well with the 4-spd/3.73 and 4.10 setup. With the 6-spd/3.42 or 3.08... I just can't see it helping that much.

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#10 700 sportsman

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Posted 22 March 2011 - 05:18 PM

My dad's truck had AFM and your could definately feel it. It was intensified with the new exhaust. With the black bear tune he turned it off, the mileage actually increased combined with the tune.

#11 Blue Sierra Owner

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Posted 22 March 2011 - 07:43 PM

There are too many variables in this to come to a good conclusion. Because none of us drive the same way, the same roads or the same truck for that matter. Here are what I have observed with my 09 5.3. I drove the truck without a tune for about 4000 miles. The AFM would kick in only when I was on a down hill slope or very flat straight. If I even thought of putting my foot on the pedal it would switch back to V8. I could not tell when it switched on or off. I had to look at the DIC to let me know. Since my tune I now have about 11000 miles on it. My mileage has not changed at all. The DIC readout has stayed at or around 14.3 miles since I picked it up from the dealer. It's about right with hand calculations I get +/- 1 mpg from what the readout says. Hope that helps.

#12 old-chevy-dude

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Posted 22 March 2011 - 08:07 PM

If I could add my .2 cents. I believe if you have great driving habits and not a lead foot, yes AFM can actually help you out and give you better gas mileage.

I have actually gotten so good at feathering the pedal I can keep a constant speed between 28 mph and about 45 mph with just AFM or V4 mode. This feathering of the pedal has saved me lots of gas and money. I can get about 2 weeks out of my tank when I feather the pedal, and thats with my normal driving mileage of around 12,000 miles a year.

However when I gas it a lot it only last me about a week, so AFM in my case has been very helpful.


thank you, I am currently getting 19.4mpg overall (over a 6 month period) on my 5.3L 4x4 with 3.42 gears and the 6 speed. all about driving habits, I drive the same way as you describe, and I can get between 600 - 700 miles per tank, which is nearly 3 weeks for me with normal driving.. on 2 trips (over 200 miles each way) I saw 24mpg averaging 60mph on the highway with cruise set on mostly flat land..


it's all about your driving habits..



My feeling (no data) is that AFM works pretty well with the 4-spd/3.73 and 4.10 setup. With the 6-spd/3.42 or 3.08... I just can't see it helping that much.


see above, but then I can't compare it to a 4sp as I never had one..

#13 TheGreekIndian

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Posted 22 March 2011 - 08:58 PM

If I could add my .2 cents. I believe if you have great driving habits and not a lead foot, yes AFM can actually help you out and give you better gas mileage.

I have actually gotten so good at feathering the pedal I can keep a constant speed between 28 mph and about 45 mph with just AFM or V4 mode. This feathering of the pedal has saved me lots of gas and money. I can get about 2 weeks out of my tank when I feather the pedal, and thats with my normal driving mileage of around 12,000 miles a year.

However when I gas it a lot it only last me about a week, so AFM in my case has been very helpful.



bingo. I have just recently started doing this. accelerating going down hill and coast to stop lights works wonders and jumps in v4 easily.
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#14 nick3941sd

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Posted 23 March 2011 - 01:02 AM

I actually saw a slight increase in my MPGs. I had the AFM turned off through the BB tune. IMO dump the AFM. You can always turn it back on.
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#15 Sir Dan

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Posted 23 March 2011 - 06:49 AM

If I could add my .2 cents. I believe if you have great driving habits and not a lead foot, yes AFM can actually help you out and give you better gas mileage.

I have actually gotten so good at feathering the pedal I can keep a constant speed between 28 mph and about 45 mph with just AFM or V4 mode. This feathering of the pedal has saved me lots of gas and money. I can get about 2 weeks out of my tank when I feather the pedal, and thats with my normal driving mileage of around 12,000 miles a year.

However when I gas it a lot it only last me about a week, so AFM in my case has been very helpful.


thank you, I am currently getting 19.4mpg overall (over a 6 month period) on my 5.3L 4x4 with 3.42 gears and the 6 speed. all about driving habits, I drive the same way as you describe, and I can get between 600 - 700 miles per tank, which is nearly 3 weeks for me with normal driving.. on 2 trips (over 200 miles each way) I saw 24mpg averaging 60mph on the highway with cruise set on mostly flat land..


it's all about your driving habits..




My feeling (no data) is that AFM works pretty well with the 4-spd/3.73 and 4.10 setup. With the 6-spd/3.42 or 3.08... I just can't see it helping that much.


see above, but then I can't compare it to a 4sp as I never had one..

Gas mileage has way more to do with driving terrain (hills), head/tail wind, and city/hwy than how you use the gas pedal. I was waiting for a mileage thread to start...they always do when gas gets much over $3.00 :)
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