AFM affected by leveling kit or larger tires?

[crushNchowda]

It would be cool if the truck would drop down into v4 when it was idling.

That would be cool, except I'm fairly certain having 1/2 the engine "off" constantly when idling could result in uneven wear/deposits. The AFM action when driving is a constant on/off scenario....but can you picture service/fleet trucks just idling on the same 4 outta 8 cylinders for extended periods of time running into issues? I can.

[Red_5]

That would be cool, except I'm fairly certain having 1/2 the engine "off" constantly when idling could result in uneven wear/deposits. The AFM action when driving is a constant on/off scenario....but can you picture service/fleet trucks just idling on the same 4 outta 8 cylinders for extended periods of time running into issues? I can.

 

Doesn't it alternate cylinders? Surely it doesn't just choose 2 cylinders on each side and only use those.

 

Why do people hate AFM so much? I only notice the change in the DIC. Does it become more noticeable with age? I have it on our Honda van and Chrysler Aspen and it never bothered me with those vehicles either.

[RhinoGuy]

 

Doesn't it alternate cylinders? Surely it doesn't just choose 2 cylinders on each side and only use those.

 

Why do people hate AFM so much? I only notice the change in the DIC. Does it become more noticeable with age? I have it on our Honda van and Chrysler Aspen and it never bothered me with those vehicles either.

My truck has a slight shudder when it goes from v4-v8. It's kind of frustrating and I don't think that the slight improvement of mpg's is worth it. It would be nice to have a disable option.

 

I didn't notice the shudder until I had around 12k miles on the truck

[Red_5]

My truck has a slight shudder when it goes from v4-v8. It's kind of frustrating and I don't think that the slight improvement of mpg's is worth it. It would be nice to have a disable option.

 

I didn't notice the shudder until I had around 12k miles on the truck

 

Thanks for the explanation. Here's to hoping GM has solved that problem.

[fondupot]

 

Doesn't it alternate cylinders? Surely it doesn't just choose 2 cylinders on each side and only use those.

 

Why do people hate AFM so much? I only notice the change in the DIC. Does it become more noticeable with age? I have it on our Honda van and Chrysler Aspen and it never bothered me with those vehicles either.

 

The same 4 cylinders shut down every time when the truck goes into AFM V4 mode. The cylinders do not alternate.

[Red_5]

 

The same 4 cylinders shut down every time when the truck goes into AFM V4 mode. The cylinders do not alternate.

 

I stand corrected. I just did a quick search, looks like it's a cost issue to only used the specialized parts on half the cylinders.

 

http://media.gm.com/content/dam/Media/microsites/product/FuelEfficiency/doc/AFM_FactSheet.pdf

[RhinoGuy]

That would be cool, except I'm fairly certain having 1/2 the engine "off" constantly when idling could result in uneven wear/deposits. The AFM action when driving is a constant on/off scenario....but can you picture service/fleet trucks just idling on the same 4 outta 8 cylinders for extended periods of time running into issues? I can.

Wouldn't half of the engine last longer?

[DanielAcosta]

Yes, oversize tires will reduce kicking into V4 unless you calibrate the truck's computer with something like a Hypertech, which I have used with great success. Currently have 57K miles with a lifetime average of 20, pretty good for a 5.3 4x4 with a small lift and 34 inch tires. V4 saves about 10-30% instantaneous fuel economy, e.g., I typically see my instantaneous readout jump from 20 in V8 to 26 and sometimes more in V4. When it goes from V4 back to V8, the instantaneous readout drops by about the same amount. Sometimes when it's right on the edge between V4-V8 the change can be real slight, on the order of just 10% or about 2mpg. Bottom line is a light foot yields better mileage whether in V4 or V8, and not correcting the truck's computer for oversize tires or a different rear end ratio will have a negative effect on your mileage in either V4 or V8.

 

I have actually climbed gentle hills at moderate speeds (under 50) in V4, but I rarely see V4 above 65 even on flat ground. Again, I have heavy oversize tires, so I would expect a truck with stock tires to do better. A lifetime average of 20 with my configuration seems pretty good to me. By comparison, my Tundra 5.7 4x4 I traded in only had a lifetime average of 15, so a 33% improvement switching to the Sierra is respectable.