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Ron.s

2014+ AFM (Active Fuel Management)

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Looking for a comparison on when AFM is active. On my 6.2 the v4 mode is active only at low speeds 45 or less and coasting. At idle it runs V8 mode, a big surprise as that's where a lot of fuel savings is available. The truck could easily pull higher speeds in V4 so what gives? Power is awesome and shifts seem about right but economy less than expected. I read that there was a top end oil problem a few months ago so wondering if GM adjusted AFM as a fix. I'm not real concerned about economy but why waste gas at idle. And yes I know the argument for bypassing AFM. Is this only my truck or other 6.2 and 5.3's similar? Trying to get educated before a dealer visit.

Ron

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Looking for a comparison on when AFM is active. On my 6.2 the v4 mode is active only at low speeds 45 or less and coasting. At idle it runs V8 mode, a big surprise as that's where a lot of fuel savings is available. The truck could easily pull higher speeds in V4 so what gives? Power is awesome and shifts seem about right but economy less than expected. I read that there was a top end oil problem a few months ago so wondering if GM adjusted AFM as a fix. I'm not real concerned about economy but why waste gas at idle. And yes I know the argument for bypassing AFM. Is this only my truck or other 6.2 and 5.3's similar? Trying to get educated before a dealer visit.

Ron

My runs V4 down to about 5mph, always V8 at idle. I've seen V4 as high as 80mph under light load and ideal conditions, but most of the time I need to be 65mph or less for any sustained V4 operation. It really comes down to the pressure under your right foot. I can actually accelerate from about 15 to 30mph under V4 if I barely touch the gas pedal; any extra pressure at all it switches to V8. It's almost like a video game, but it does work.

 

Other posters with the 6.2 seem to have better results than you are indicating. There have been several ECM updates with the 5.3 I have; don't know if there are any updates for the 6.2 See my signature block for more info on my truck's specs. Good luck with yours.

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Mine is similar to Danial. 5.3 4x4 also

 

I dont understand why they didn't have idle at v4.

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It probably also depends on the axle ratio of the truck.

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Thanks guys-guess they all go V8 at idle. Mine will go V4 at higher speeds but not accelerating or constant speed....only easing off gas or down hill. Seems like there is not much benefit to have AFM for the short duration it's active.

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I could see idling in V4 mode when in Park, but I don't like the idea of idling in V4 in when in drive. I want to have all the V8 power when taking off from a standstill.

 

I do wish GM made AFM selectable. A lot of other auto manufacturers have "active-ECO" modes that dumb down the throttle to give better fuel economy. It could be very easily implemented to have an ECO button somewhere on the dash that enables/disables AFM. It would help a lot of the gripers that hate AFM, but would still allow the people who don't mind it to get a little better MPG's when warranted.

 

Majority of my driving is speeds up to 50 mph. When I finally get up to speed, my truck stays in v4 mod most of the time. My area is relatively flat, so it only goes into V8 when a hit a slight hill, or incline. The only bane to my driving is a lot of stop lights. So i have short runs of cruising. Then coming to a stop again. Not the best when trying to get good MPG's in a big truck. But I still manage to get between 17-18.

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I could see idling in V4 mode when in Park, but I don't like the idea of idling in V4 in when in drive. I want to have all the V8 power when taking off from a standstill.

 

I do wish GM made AFM selectable. A lot of other auto manufacturers have "active-ECO" modes that dumb down the throttle to give better fuel economy. It could be very easily implemented to have an ECO button somewhere on the dash that enables/disables AFM. It would help a lot of the gripers that hate AFM, but would still allow the people who don't mind it to get a little better MPG's when warranted.

 

Majority of my driving is speeds up to 50 mph. When I finally get up to speed, my truck stays in v4 mod most of the time. My area is relatively flat, so it only goes into V8 when a hit a slight hill, or incline. The only bane to my driving is a lot of stop lights. So i have short runs of cruising. Then coming to a stop again. Not the best when trying to get good MPG's in a big truck. But I still manage to get between 17-18.

 

 

My sisters terrain has an ECO button. I don't know what it does though because I am pretty sure those Terrains are 4Cyl's how it is.

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At the rate the V4/AFM engages on my truck it wont do crap for the gas mileage. If it was not for me wanting to lose my warranty I would have tuned it out already. Maybe once HPT figures a way around the flash counter I will tune the AFM out and then make some adjustments to the transmission calibration and some of the non-fueling stuff on the engine side.

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How do you design an AFM system for a single cylinder motorcycle engine?

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How do you design an AFM system for a single cylinder motorcycle engine?

 

You wouldnt. A 1 cylinder motorcycle engine will already get 60 mpgs

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Why are people so concerned about this topic. I do not understand it. Just drive it. End of story. And yes, even if you can't figure out why the truck has it, it is to save fuel.

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For me it's a fun video game seeing how much time I can spend in V4. My best so far is accelerating from 15 all the way to 50 on just 4 cylinders. My instantaneous readout usually goes up about 20% when it changes from V8 to V4, so it does save some gas. With a small lift and 34" tires, 20mpg overall seems pretty good to me.

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The reason that the engine is not in V4 mode at idle is that the idle would sounds terrible, like a tractor. I would much rather hear the harmonious sound of 8 cylinders than 4.

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GM doesn't allow AFM at idle because it would be too rough, though the noise would likely be unpleasant too.

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