Promising better fuel economy for AFM engines, the Range

Buck's Truck · April 20, 2014

Driving in the V4 mode the instant mileage off the DIC can be all over the place from 99 mpg coasting downhill to 22-32 mpg at 65 mph. I have seen 72 mpg in M5 which is locked in V8 coasting downhill. So it can be all over the range, really hard to judge. Like U said there are a thousand factors involved.

Hi Gang,

First post here.

I shifted into M5 yesterday when I went to get gas. But, on a slight downhill dip, the DIC showed V4 was engaged until the uphill grade. Maybe M5 forces V8-only in pre-2012 GM trucks?

Had a lot of stuttering after i bought Kangaroo gas (never again!) a couple of weeks back. But, otherwise, I haven't had any problems with AFM on my truck. Feel bad for those who do, though.

Also, I've read a lot about an AFM "fix" starting with the 2011 models. Could someone flesh this out?

Thanks! Great forum!

Bucky

j-ten-ner · April 20, 2014

Are you sure it was in M5 and not M6?

Maybe you pushed "+" by accident.

so long

j-ten-ner

Buck's Truck · April 21, 2014

Yup, it was M5. Checked M6, too, which went into V4.

I'll double-check it tomorrow to make sure.

Bucky

Bassboats · April 22, 2014

I used a Hypertech programmer to disable AFM on my 2011 5.3L 1500 for a year long test. Lost 1.5-2mpg at speeds under 50mph and a solid 2mpg at interstate speeds. Went back to "stock" mode several months ago to re-activate AFM. Don't like the warbling exhaust as AFM kicks in, but I know it's saving fuel when it does.

Today's AFM iterations are more aggressive in how much throttle can be applied before engine goes back to V8 mode, which helps both city and highway mpg.

Buck's Truck · April 23, 2014

Are you sure it was in M5 and not M6?

Maybe you pushed "+" by accident.

so long

j-ten-ner

You were right! Ran the truck in M5 on the same route today. Didn't go into V4 once.

I must've been in M6, like you said.

Bucky

Crf450r420 · May 4, 2014

I'm assuming you can buy a new truck without AFM right? Too many electronic gizmos on new trucks these days. And then you have to buy another plug and play module to override something that shouldn't have been there in the first place, AFM. I guess it might gain you 2-3 mpg but I'd rather just have a V8 all the time and just deal with it. Uneven cylinder wear doesn't sound like a very good tradeoff to slightly better fuel economy. Though its funny that cylinder wear is even an issue, these trucks should run 300,000 miles with no cylinder wear. Guess they just don't build them like they used to. Building them to sell and not to last.

After reading this I thought it was an old guy, but you're only 40. (according to profile)

They use to build them with carbs and you couldn't get more than 80k to 100k without rebuilding. EFI can't make it the 300K you are talking about. They also use to build them with flat tappet lifters and you would lose the exhaust lobe about 100k. Then it wouldn't shut off and run on after the key was shut off. Now with the EPA destroying oil and removing the ZDDP's you won't be able to get 10k out of those cams without an additive or race oil.

Now for the thread. The oil pumps in these motor have to have a capacity above what is normal and they have a bleed off in the pan to prevent over pressuring the system at times. They later added a shield to ensure this oil was directed down to the into the pan only. Now we thought like many that system activated to take out the lifters from working to deactivate the cylinders, but when we modified a crate motor we tired it with those lifters left into the motor. Then we put on the standard LS2 style block of valley cover to replace the DOD or AFM cover. Thinking this would disable the system and we could just use the lifters as is to run a full V8. We were surprised to find the motor ran as a 4 cyl. This means these lifters are built to pump up easy and in order to run as a V8 the extra oil is bleed off by the plate. Then to get V4 mode the oil bleeds are blocked off. These means if the oil bleed off is causing any of the oil consumption issues in the AFM, it is likely going to be worse by keeping it in V8 all of the time. Just saying.

Crf450r420 · May 7, 2014

Why wouldn't the computer shut down 1,3,5,&7 cylinders say the first time AFM cuts in and next time 2,4,6,&8 shut down......even up the wear! It's computerized. ..they can make it do whatever they want!

They only have 4 cylinders with the provisions to the control the special lifters. The rest of the lifters are normal. I'm pretty sure most people worried about the wear from this have never opened any of these motors. On top of that why you should really be worried about in my eyes is the second cam lobe from the VVT which has the center section cut out to supply the oil to that system. This means there isn't as much surface area hear to carry the load. You can see it in the image here.

http://blogs.cars.com/.a/6a00d83451b3c669e2012876afab1f970c-800wi