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Afm Question

Bowler807

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Bowler807 Enthusiast

Bowler807

Posted
Posted

I already searched but could not find anything on this.

 

My 08 now has 500 miles. We are still in the honeymoon stage. I am starting to notice some things however. One in particular is when the AFM disengages. Many many posts here say that the AFM is seamless. I take that to mean that I shouldn't be able to tell when it kicks in and out.

 

What happens to me is while cruising in V4 I increase the the gas slightly to maintain speed. When the truck shifts back into V8 mode from V4, it seems like the torque converter unlocks and the RPM's increase about 300, there is a slight acceleration then everything is fine. If in V8 mode and I increase the gas slightly to maintain speed, nothing happens. There is no torque converter unlock, no slight acceleration, just my speed maintained.

 

Is this normal???

JNG3 Enthusiast

JNG3

Posted
Posted

I don't 'feel' anything but I do notice the needle on the tach moves a little. It's always puzzled me but then again I can get 16.5 to 17.9 mpg out of a 300+ hp 4x4 truck, so I'm not complaining. My '99 2 wheel drive 4.8 Silverado was only slightly better and the Ford I owned for two years inbetween the Silverado on my current Sierra was un under powered dog and was lucky to see 16 mpg.

Nick The Great Senior Enthusiast

Nick The Great

Posted
Posted

Hang on to your butt! This topic could get crazy :thumbs:

 

I can't feel my AFM. If I didn't have my DIC on instant econonmy, I'd never know. :loser: I think something's up with yours. Other people on have have said this before.

 

I had Justin at Blackbear up mine a little bit and it stays on a lot more, especially in town. I'm going to be curious to get a few tanks of fuel with different driving conditions to compare the mileage. :bs:

pm26 Senior Enthusiast

pm26

Posted
Posted
Hang on to your butt! This topic could get crazy :thumbs:

 

Yes, it could, especially when I and Super Stealth start chiming in. :loser:

 

Seriosly though, there seems to be a small percentage of AFM engines out there that exhibit somewhat rougher than "seamless" transition from the V4 to V8 mode. This is why those who have smoothly operating systems like them, and those who have rougher ones hate them. In GM's book, this situation is "normal".

 

It is similar to the piston slap issue: most do not have a serious case of it, a very small percentage do. The AFM system is unfortunately a crap shoot too - you can get a "seamless" truck or you can get a clunky one.

motoxxx Enthusiast

motoxxx

Posted
Posted

Have someone custom tune your truck to get rid of the AFM! A custom tune will increase your MPG anyway. I jumped from around 14.2 to 16.3 MPG.

 

If not, you could drive your new truck off a cliff. My truck must be one of the "piece of craps" because hearing the word seamless and AFM in the same sentence is a joke. I am very particular, so someone on this board might say my truck is seamless if they owned it. So you have to do whats best for you. Good luck.

VMax2007 Senior Enthusiast

VMax2007

Posted
Posted
Have someone custom tune your truck to get rid of the AFM! A custom tune will increase your MPG anyway. I jumped from around 14.2 to 16.3 MPG.

 

If not, you could drive your new truck off a cliff. My truck must be one of the "piece of craps" because hearing the word seamless and AFM in the same sentence is a joke. I am very particular, so someone on this board might say my truck is seamless if they owned it. So you have to do whats best for you. Good luck.

 

I can guarantee you I am just as particular as you are and let me assure you, mine is 100% seamless. Just because yours is not, does not mean everyone else's is the same way.

 

And I am not defending AFM as I agree that it's a joke, but only because I do not believe it saves me more than a nickel/tank of gas.

Nick The Great Senior Enthusiast

Nick The Great

Posted
Posted
Have someone custom tune your truck to get rid of the AFM! A custom tune will increase your MPG anyway. I jumped from around 14.2 to 16.3 MPG.

 

If not, you could drive your new truck off a cliff. My truck must be one of the "piece of craps" because hearing the word seamless and AFM in the same sentence is a joke. I am very particular, so someone on this board might say my truck is seamless if they owned it. So you have to do whats best for you. Good luck.

 

I can guarantee you I am just as particular as you are and let me assure you, mine is 100% seamless. Just because yours is not, does not mean everyone else's is the same way.

 

And I am not defending AFM as I agree that it's a joke, but only because I do not believe it saves me more than a nickel/tank of gas.

 

 

+5 I think the tech does have merit for smaller, lighter cars. Justin (Blackbear) was telling me that the 5.3L engine isn't really a good platform for it. He did mention the the 6.0 is much better suited. Not quite sure what he meant by that. :thumbs:

crepitus Enthusiast

crepitus

Posted
Posted

mine with 1200 miles on it is not a "seamless" one. I cant feel it go in but once its in the truck seems to run a bit rougher. Just had it at the dealer Wednesday for them to check it out. I heard there was a new ECM program to make it better. Mine was the latest. They said its normal.

 

I wonder if the people with these "seamless" AFM truck live in flat areas. Its only really noticable when i hit a slight grade that i really feel anything. or maybe they are just always traveling downhill. :thumbs:

VMax2007 Senior Enthusiast

VMax2007

Posted
Posted
mine with 1200 miles on it is not a "seamless" one. I cant feel it go in but once its in the truck seems to run a bit rougher. Just had it at the dealer Wednesday for them to check it out. I heard there was a new ECM program to make it better. Mine was the latest. They said its normal.

 

I wonder if the people with these "seamless" AFM truck live in flat areas. Its only really noticable when i hit a slight grade that i really feel anything. or maybe they are just always traveling downhill. :thumbs:

 

Actually, there is some truth to that, since mine will NEVER be in 4 mode while on any kind of uphill grade. The only time mine uses 4 mode is on level (or downhill) roads while slowing down or maintaining speed under 60-65 MPH with no load on the engine. That is why I think it's a joke for gas savings.

 

On my recent Blackbear tune, Justin said he would bump it up to stay active a bit more, and it does stay on slightly more now, but not much.

 

Are you guys sure you aren't feeling the TCC lock and unlock?

mhenshaw Senior Enthusiast

mhenshaw

Posted
Posted

Mine is seamless most of the time, but sometimes I can feel it switch to V8. I think it's because it bogs out in V4 then when it switchs back to V8 there is no more bogging and it revs back up.

Huntervh Enthusiast

Huntervh

Posted
Posted

On cold mornings I can feel a shift, otherwise it is not to bad. Although it does piss me off when it goes between V4 and V8 about 10 times in the span of 30 seconds.

mdauwald Enthusiast

mdauwald

Posted
Posted

I don't feel mine switch at all but I have learned to hear when it switches. If mine goes into V4 while on a grade the truck will slow down if it doesn't get more gas. That's not much different than any 4 cylinder behaves on hills. I have also noticed that AC use really inhibits the ability to use V4 up hills too. Since I can easily pick out V4 by sound I am really hesitant to upgrade the exhaust to the magnaflow catback I have been considering. One more thing, I got some crappy gas and that also modified AFM execution.

VMax2007 Senior Enthusiast

VMax2007

Posted
Posted

Mine is seamless, but since it is also worthless, I may have Justin turn it off. I haven't decided yet.

 

Anyone think turning it off could lessen the chances of something failing? I know I read the potential lifter issue cannot be averted by turning it off, but maybe other things could?

pm26 Senior Enthusiast

pm26

Posted
Posted
On cold mornings I can feel a shift, otherwise it is not to bad. Although it does piss me off when it goes between V4 and V8 about 10 times in the span of 30 seconds.

 

I noticed the same thing when I test drove a new 2007 Impala SS with a 5.3 AFM engine. The eginne switched back and forth between 4 and 8 cylinders constantly, maybe 100 times during a short test drive.

 

Does the torque converter lock and unlock every time the AFM switches in and out of the 8 cylinder mode? That has got to wear something out in time.

 

If I had one of these AFM engines, I would seriously consider a custom tune like VMax suggests.

 

In fact, I would be a proud owner of that 2007 Impala SS if it wasn't for that $%^&* AFM crap. Is it possible to tune the Impala SS too to deactivate the system?

Rat4go Enthusiast

Rat4go

Posted
Posted

The way AFM was explained to me, the electronic throttle needs to be more open in V4 to make the same torque as in V8. When it switches from V4 to V8, the throttle needs to close some to get to a point where the torque is the same after the switch. I've also been told that the torque converter does 'unlock' for a split second to help 'mask' any error in the throttle position and before/after torque. In the 07 suburban that I drive, I've noticed the V4-V8 transition more when the pedal is moving slightly during the V4 to V8 transition (stepping in to accelerate or go up a hill), but if you step in pretty fast to pass someone or , it is more seemless.

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