2014+ AFM (Active Fuel Management)

CAtaylor · August 8, 2014

I would have to say that the V4 mode definitely helps, atleast in my setup. I work 347 miles from home and I make the drive up to 2 days a week. Every time I get my truck on the road it is for the long haul. If I set the cruise below 73mph my V4 mode will regularly kick in and will hold this in less I am going up a hill. Granted my truck is turning 2250 rpm at this speed. Cruise set at 73 I can get up to 17.6 mpg. At 75 mph 4 cylinder does not kick in except down hill and I am at 15 mpg. I have thought about tuning it out but as much highway driving as I do I have decided not too yet. Set the cruise at 65 and 4 cylinder mode will stay on 85% of the time and I will get close to 19 mpg. I can watch the little fuel economy bar and tell when it is going to shift. Below 17 mpg and it is in v-8, 17-18 mpg and it shifts into v4. Once it is in v4 it will stay in till I pull the mpg readout down to 16 with the skinny pedal and it will shift back to v8. This is with 6" lift, 35 " tires and 4.56 gears. I would love to take a trip and keep it at 65 just to see what it would do but I don't have the patience as that will add another 40 min to an already boring drive.

Wormydog1724 · August 8, 2014

I don't get all the hate for the afm. I drive 60 miles round trip everyday, half at 55 it under. The rest at 65-70. I think it helps. I guess I should tune it out for a week and do a test.

KARNUT · August 8, 2014

I don't get all the hate for the afm. I drive 60 miles round trip everyday, half at 55 it under. The rest at 65-70. I think it helps. I guess I should tune it out for a week and do a test.

Before I messed with the exhaust I never notice it either, once I change the exhaust the helicopter showed up and a little V4 vibration. After thinking about it for a while I found the cheapest can tune I could find. For a caned tune it works good. My fuel mileage on a trip last wk at 72 miles an hour was just under 22 miles per gallon. So Ill keep the exhaust and no V4.

BigBadSierra · August 8, 2014

I think the varible valve timing is doing more to save gas then the V4 AFM mode is.

ryandemo84 · August 8, 2014

I don't get all the hate for the afm. I drive 60 miles round trip everyday, half at 55 it under. The rest at 65-70. I think it helps. I guess I should tune it out for a week and do a test.

Your daily drive sounds ideal for AFM. I drive the same distance daily but on interstate. No V4 above 72 for me unless downhill. Feels like it keeps shifting so i see no benefit. I still avg 19 mpg over my last 400 miles. Thats at 75-80mph for 80 percent of my daily drive. The other 20 percent city driving I dont see gains from V4. A good tune would make my driving a lot better.

TxTruckMan · August 13, 2014

Second post, guy admits it will only go into V4 after 65 in the right conditions, because starting at 45 wind adds resistance to moving and by 65 it has added enough that the truck doesn't get more MPG in V4 over V8. If I could get into V4 at 70 I'd get better than the rated MPG, but as it is I get about the rated MPG at 70 mph going between 19 and 21 depending on the winds in relation to my direction. I have not tried the trailer tow mode that high yet, but found down low that it often is a wash as the higher revs in V4 use as much fuel as V8 in the next gear. I'm not trying to be an ass by stating the facts of it normal because of physics. V4 is not an interstate help or they would have a better highway rating for MPG. I'm currently running 48 psi in my tires and truck is stock exterior except for the hard bed cover and power steps and with cruise control still no V4 flat ground. If you are in fact getting it to work more than most I'd love to learn how. No point in using more gas than I need.

Put me in the camp of getting V4 at speeds up to nearly 80. Mine kicks in all the time. And V4 is more intended for highway speeds than around town. It won't kick in when you're accelerating from a stop, only when you're at steady speeds or easy on the throttle. If you drive with a heavy foot, you won't see any difference in mileage because you won't be in V4 often.

Two weeks ago I made a 500 mile round trip to Houston and noticed that RPMs would jump maybe 100 rpms when in V4. But when your only firing half of the cylinders, your're still saving. At 70, I'd be getting around 20-22 in V8. Then it would switch over to V4 and the instantaneous economy would jump to 24/26 or so. Once I hit 80, it would only come on when heading down slight hills.

Crf450r420 · August 18, 2014

Looks like the little 3.800 bore has less drag than the 4.065 bore.

CAtaylor · August 19, 2014

Mine will accelerate in v-4. As soon as it hits 3rd gear it shifts to v4 and will stay there until I get in the throttle more or it hits around 60 mph. Granted the people behind me would like to skull drag me down the road. Flat road mine will run v4 at 70 mph till it times out.

Edited August 19, 2014 by CAtaylor

bass mechanic · August 31, 2014

Personally, I don't think V4 does anything to save gas.

Here's the deal..

So the truck uses 1/2 the engine, your still dragging around 4 dead cylinders and still pushing the same truck down the road at the same speed. Your just making 4 cyls do the same work of 8

Fact is, now that my 6.2 is supercharged I still get consistently 22 highway mpg as before. My v4 is tuned out due to the addition of the SC and despite the additional accessory of the sc and it's parasitic losses (although small due to it's bypass mode)

IMO afm is more of a marketing gimmick than anything else.

It may be that GM knew they needed a "new technology" to get the buyers to believe the advertised mpg was possible.

Another theory is that if AFM actually does anything of value I bet it has more to do with limiting the amount of power you can use.

I've spent a lot of time on the highway learning how to get better mpgs I've found that unless your always aware of you foot on the gas, you will unintentionally change the pressure on the gas to maintain speed, this is why some people get better mpg than others.

Cruise control does not anticipate hills or valleys the way a human can.

I actually rest my foot against the trans tunnel to make certain it does not move once I've attained the speed I want to keep. It gives me precise throttle control by rotating the ankle so I can precisely apply the throttle as needed.

Now that I'm running v8 all the time I see no difference in mpg's and why would it? I think it has everything to do with exact throttle control. Gimmicks like this just make it easier for the operator to maintain speed.

My Lexus has a similar tool, economy mode, it just makes the gas pedal sloppy or sluggish with regard to throttle control. It's rated 29 mpg highway and I consistently get 33 using the same driving habit and I never use Eco mode in it

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BigBadSierra · September 1, 2014

V4 helps a bit. I think the new variable valve timing is making the biggest difference in the new engines..

I think most of the V4 savings is actually coming when stopping. Just cutting the fuel while stopping and the drag on the engine also helps to slow down.

Hence the big difference from the older engines with the V4 mode versus the new engine.

bass mechanic · September 1, 2014

Not true, anytime you decelerate (foot off the gas) in v4 or v8 and the mpg reads 99 mpg there is ZERO fuel used. The injectors are not even open. There is absolutely no good reason to burn fuel if the engine is spinning above 1000 rpm. You could say the engine is dead and fuel is added back just before it returns to idle. It's also in open loop mode since there is nothing to monitor on the o2 sensors since there is no combustion.

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14SLTZ71 · September 1, 2014

...?

Edited September 1, 2014 by 14LTZZ71

scott19677 · September 1, 2014

I agree V4 is horrible!! Why didn't they make M6 stay in V8 mode.

Yeah , I guess Im just venting a little. I full am prepared to get my truck back and it look like a bunch homeless people have had a 'SOUP KITCHEN' ( the OTHER GUYs movie) in it. Every week when I call they aren't giving me the warm and fuzzes. Its almost like there trying to cover up a murder scene L.O.L Oh well sorry to hijack.

Edited September 3, 2014 by scott19677

14SLTZ71 · September 1, 2014

Yeah , I guess Im just venting a little. I full am prepared to get my truck back and it look like a bunch homeless people have had a 'SOUP KITCHEN' ( the Good GUYs movie) in it. Every week when I call they aren't giving me the warm and fuzzes. Its almost like there trying to cover up a murder scene L.O.L Oh well sorry to hijack.

This should prepare you so that you won't be so shocked when you pick it up. Maybe they will have a nice warm bowl waiting for you at the service counter. Lol

scott19677 · September 1, 2014

This should prepare you so that you won't be so shocked when you pick it up. Maybe they will have a nice warm bowl waiting for you at the service counter. Lol

Could be worse! Im all fired up now LOL . Im calling the dealer and tell them Im coming by to look for my phone charger. See what the hell they are doing. Insert OO7 theme in HERE.