Active Fuel Management

tobias · February 23, 2008

Guys,

I am trying to help some of the guys on the fence get a feeling for how those of us who have AFM feel about it. Again, please only vote if you own(ed) a GM vehicle with AFM.

Thanks,

Daddy

VMax2007 · February 23, 2008

I voted "no". Not because I am "afraid" of new technology or AFM causing this engine to have a shorter life or any of that BS. I voted no because it virtually NEVER is activated unless I am coasting or maintaining a speed under 60 mph on a flat or declining freeway with cruise on and AC off. I question how much (if any) fuel this really saves. For me, I am convinced it is negligible, because I rarely drive on the freeway at cruising speed, and when I do, I am almost always above 60-65 mph. I would be willing to bet AFM has maybe saved me 10 gallons of gas over the past year (10K miles) TOTAL!!! I like the idea of AFM, but if they cannot make it so it can be activated under any load at all, then it is useless in IMO.

With that said, I do NOT think they should "scrap" it, I think they need to keep on developing it to make it better.

What really gets me is people love to bash GM for not being a "leader", yet when they do lead with new innovations, they then get ridiculed for it. They can't win (oh, and this AFM is NOTHING like the 8-6-4 technology used in the Caddys in the 80's, so don't tell me AFM is not new technology for GM).

Also, why do most people assume this AFM system is so "complicated"? It really isn't all that complex and it doesn't add all that many new parts to an engine. It's basically just a different lifter in 4 of the cyls and some hydraulic solenoids controlled by the engines computer, which is already extremely complex anyway.

VVT is also a new technology that adds complexity to an engine, but nobody seems too worried about that (currently, this is NOT on the 5.3, just the 6.0 and 6.2 engines). I actually believe VVT saves me more fuel than AFM does.

My .02

excaliber · February 23, 2008

I don't like the AFM. I think I could do almost as well by just keeping my foot out of it. There were two things I didn't like when I test drove the GMC sierra with the 5.3

One was no 6.5' bed on the CC and the other was the AFM. I could not get it to kick in while driving it and I thought it was of no use to me. I was told that they were going to have trouble with it by a friend who's a longtime engine builder. he told me this several months ago.

He said it just doesn't work and they would have trouble. i guess he was right.

What the heck am I going to do now? I wanted a CC Sierra with a 6.5' bed but since they don't make one and now throw in the AFM, GM is no longer at the top of my list. Toyota's Tundra is a POS and they are out.

Ford's F150 is the only one I like who builds the CC with a 6.5' bed so maybe I'll wait for the 010's to see how all these trucks sort themselves out.

I hope GM gets this straightened out soon.

ken1mod · February 23, 2008

Gentlemen,

AFM is exactly like the old Cadillac system except that it does not use the 6 cylinder mode. In 6, the old Caddys vibrated because of the uneven firing and that is what killed it. Of course, the controls are better now. That is why AFM goes right to 4 cyl mode.

I do agree that if the AFM can not be used at least 50% of the time, it is a waste of technology, complexity and weight. I am disappointed that it actually engages so sparingly.

Ken

huero626 · February 23, 2008

I personally don't like AFM, I bought a V8 for a reason. I didn't buy it to save gas.

pm26 · February 23, 2008

I have some problems with this "fuel saving" philosophy. On one hand, they introduce the AFM system as a fuel saving measure. On the other hand they eliminate all manual transmissions from the entire GM full size truck lineup. That to me is total BS. What is wrong with a 4.3 V6 work truck and 5 speed manual transmission? Or any pickup for that matter? A well designed manual transmission could save you more fuel than the AFM system IMHO.

Also, why not a small fuel efficient diesel coupled to a 5 or 6 speed manual transmission with a good ergonomic shifter and a well designed light clutch? That to me would be a far more prudent approach. Unfortunately with our lazy public, this approach is not welcome. Instead they need a 1,000 HP engine, auto transmissions, cooled and heated cupholders, and of course some magical system that would still deliver 30 MPG out of that engine.

You go to some other country, like Australia, for example, and you can buy all kinds of nice SUVs and small pickups with small turbo diesel engines and manual transmissions. I even saw Land Rovers with the same set up. Nothing like this here in the US.

You can argue all you want about manual transmission effect on fuel economy, but with certain engines, like small diesels, you get much better economy with a manual. For example, a VW Jetta Wagon with a turbodiesel and 5 speed manual was rated at 50 MPG HWY, but only 38 MPG with an auto transmission.

d3athsong · February 23, 2008

Also, why not a small fuel efficient diesel couple to a 5 or 6 speed manual transmission with a good ergonomic shifter and a well designed light clutch?

You can argue all you want about manual transmission effect on fuel economy, but with certain engines, like small diesels, you get much better economy with a manual. Fro example, a VW Jetta Wagon with a turbodiesel and 5 speed manual was rated at 50 MPG HWY, but only 38 with an auto transmission.

Well, diesels dont run as clean as gas. That creates a problem for those states with emission standards. Typically, diesels are for pulling, not your daily driver. And th enew gm diesel coming out in a few years is supposed to be decent on milage, but will probably cost more to buy then a gas and be more expensive to run, with diesel prices being higher then gas. Not quite sure it will sell well at all.

The jetta is a small, light car, not a fullsize truck. We know that the government ratings dont mean jack. My trucks RATED at 29MPG, but im pretty sure i wont be seeing that.

iminaquagmire · February 23, 2008

I was on the fence before. But after my tune I like it. Justin at Blackbear changed the settings so that it kicks in and stays on more often. From the factory, he said it is programmed to go back to 8 cylinders at 6% throttle. That is nothing for a 315 hp engine. It does stay on longer under more load than before but functions exactly the way it did before where if I need the power, the change to 8 cylinders is still seamless and fast. Couple that the other stuff he changed, and I routinely see 20-25mpg in V8 mode and 30+ in V4 on the DIC under the same conditions where V8 mode might have been 15 or 16 and V4 mode virtually nonexistent. Now I'm not saying I'm getting 25mpg out of this but it is better. To what extent I'm not sure as I've only run half a tank through it so far and can't really tell on it yet.

hubbycap · February 23, 2008

After 10K miles I'm tuned into my truck and what it is doing. I do notice the AFM engaging and I notice that it doesn't engage when I need the power of a V8. It's one more of the dozens of subsystems that are harmoniously moving Silvia down the road. If it delays a fuel stop a few miles, good. I really can't object to its operation.

There is no ONE answer; a tenth of a MPG here and a tenth there. Shift points, lubricants, drag coefficients, rolling resistance, ignition. Even with computer oversight, the internal combustion engine design can only be refined to a finite point. In the end there is a limit to how little fuel can be used to move 5000+ lbs.

VW and other small vehicles achieve their fantastic fuel efficiencies by moving 3000lbs, and a few hundred pound motorcycle bests those figures. If you only need to move 1 fat ass, get a motorcycle.

My 5.3 averages about 17mpg with my foot. My '95 5.7 was about 15. An army of engineers have squeezed another 2mpg out of dino juice over 12 years while it added another 100 HP. Countless man hours are now being poured into each 1/100 of a mpg increase. We've long passed the point of diminished return.

I need my truck for business, maybe I could function with one of those tiny trucks most of the time but I'm willing to pay for the comfort and safety of some tonnage.

When I need to move my family around, I've got a 25-30 mpg passenger car. When I need a truck, I need a truck.

Eddie Haskell · February 24, 2008

If there were not fuel economy atvantages then GM engineers would not have used AFM. Now, it may not work to your benifit depending on how and where you drive but I would trust a GM engineer over some guys seat of the pants observation.

I always thought VVT had more to do with delivering torque at more favorable rpms than fuel economy. Correct me if Im wrong.

Looking at the 08 trucks the 5.3 with 3.73 is 15/20 mpg. THis is a reg cab shortbed. The 4.3 is the same and the 4.8 is one mpg worse. AFM I think is a good thing and maybe tuners will be able to do something with the programming to help each persons situation.

hubbycap · February 24, 2008

If there were not fuel economy atvantages then GM engineers would not have used AFM. Now, it may not work to your benifit depending on how and where you drive but I would trust a GM engineer over some guys seat of the pants observation.

I always thought VVT had more to do with delivering torque at more favorable rpms than fuel economy. Correct me if Im wrong.

Looking at the 08 trucks the 5.3 with 3.73 is 15/20 mpg. THis is a reg cab shortbed. The 4.3 is the same and the 4.8 is one mpg worse. AFM I think is a good thing and maybe tuners will be able to do something with the programming to help each persons situation.

Yeah, guys that live out in the flat plains areas can probably drive for extended V4 periods and really get the goody out of this system. I figure it helps me some in gentle rolling terrain, but like iminaquagmire sez, if you can extend the range from under 6% to saaayy under 9% it may be more beneficial by being active more often and longer.

fbachman · February 24, 2008

AFM is OK... I must say I am more in the camp of "not minding it" as opposed to "liking or disliking it".

My take on it is this:

My guess is that the obligatory standardized test protocols that GM went/goes thru to establish mileage and EPA pollution benchmarks is such that the AFM significantly improved the rating of the vehicle whilst undergoing these tests, SPECIFICALLY.

I am not sure that the AFM goal of GM "out of the box" was to boost mileage significantly, although it does seem to help some.

Let's face it, I have a 5.3 NBS that routinely does better than 14mpg in city/suburban driving and got better than 18mpg on my last highway trip averaging 79mph. That's pretty good in my mind. Others report even better numbers than mine.

I agree on the reliability concern, but the 100,000 mile powertrain warranty kind of put my mind at ease. Although, being stranded due to the AFM nullifies any warranty at that moment. You're still stranded. On the other hand, I have not heard of many AFM failures.

I guess I'm OK with it...

Paul58 · February 24, 2008

I have no issue with AFM other than I wish it would stay engaged a bit longer. I did notice that after I installed my Edge Evolution it seems to stay a bit longer than stock, but I feel it could still stay activated even longer, especially on highway trips. It seems to kick into V8 mode way before it needs to even on slight grades.

I get a consistent 17 mpg on my daily commute (straight city driving averaging 40- 45 mph speed limits with 39 stop lights on the 20 mile route) and 20+ mpg on the highway averaging 75 mph. So, I feel it definitely helps!

By comparison, my mid-sized 05 Nissan Frontier with a V6 and only a 5000 Lbs towing capacity averaged 15 mpg city and 19 mpg highway! So, for a full-sized truck with a V8 and 7700 lbs towing capacity, I feel I'm much better off with this truck!

VMax2007 · February 24, 2008

If there were not fuel economy atvantages then GM engineers would not have used AFM. Now, it may not work to your benifit depending on how and where you drive but I would trust a GM engineer over some guys seat of the pants observation.

I always thought VVT had more to do with delivering torque at more favorable rpms than fuel economy. Correct me if Im wrong.

Looking at the 08 trucks the 5.3 with 3.73 is 15/20 mpg. THis is a reg cab shortbed. The 4.3 is the same and the 4.8 is one mpg worse. AFM I think is a good thing and maybe tuners will be able to do something with the programming to help each persons situation.

Yes, VVT is meant to optimize power at a given RPM, but with that also comes efficiency. If you are optimizing the power at, say, 2000 RPMs by phasing the cam, then the engine is working at peak efficiency at that given RPM also. So, yes, VVT does affect fuel mileage. Even moreso in DOHC applications which allow independent timing adjustment between intake and exhaust valves.

Yes, GM incorporated AFM to increase efficiency, and to some extent it does. I just feel that in my useage (and probably the majority of owners will agree) that the increase in very minute and nearly negligible in my case. GM probably did it more for CAFE and increasing it's "Green Image" than anything (marketing).

Doomsday · February 24, 2008

Voted no, for the same reason as this:

I voted "no". Not because I am "afraid" of new technology or AFM causing this engine to have a shorter life or any of that BS. I voted no because it virtually NEVER is activated unless I am coasting or maintaining a speed under 60 mph on a flat or declining freeway with cruise on and AC off. I question how much (if any) fuel this really saves. For me, I am convinced it is negligible, because I rarely drive on the freeway at cruising speed, and when I do, I am almost always above 60-65 mph. I would be willing to bet AFM has maybe saved me 10 gallons of gas over the past year (10K miles) TOTAL!!! I like the idea of AFM, but if they cannot make it so it can be activated under any load at all, then it is useless in IMO.

With that said, I do NOT think they should "scrap" it, I think they need to keep on developing it to make it better.

What really gets me is people love to bash GM for not being a "leader", yet when they do lead with new innovations, they then get ridiculed for it. They can't win (oh, and this AFM is NOTHING like the 8-6-4 technology used in the Caddys in the 80's, so don't tell me AFM is not new technology for GM).

Also, why do most people assume this AFM system is so "complicated"? It really isn't all that complex and it doesn't add all that many new parts to an engine. It's basically just a different lifter in 4 of the cyls and some hydraulic solenoids controlled by the engines computer, which is already extremely complex anyway.

VVT is also a new technology that adds complexity to an engine, but nobody seems too worried about that (currently, this is NOT on the 5.3, just the 6.0 and 6.2 engines). I actually believe VVT saves me more fuel than AFM does.

My .02