I was just thinking earlier today and this may sound like a dumb question but its got me....

When the truck switches into v4 mode i know 4 of the cylinders shut off fuel and spark, So my question is being as heavy as the truck is, wouldn't the 4 working cylinders be working harder to keep the truck moving? Also as a cause of this being more fuel is delivered to the cylinders (still less then v8 mode) but wouldn't that run rich and cause bad plugs and possibly more wear on the rings?? Just a thought.

 

they probly made sure none of this would happen before they released it to the public

 

The parameters which the V4 mode operates is only at cruise and your truck probably needs about 50 hp to roll down the highway at that point. That hp amount is only a guess but what I am trying to say is that it doesn't take much power to roll down the highway at steady speeds.
The fuel ratio doesn't change so there isn't really any chance in fouling the plugs.
As for the rings...I am not so sure about this one. All the pistons are still spinning so I wouldn't think the rings would see any additional wear. At least that is what GM says regarding their durability and maintenance intervals.

 

makes sence

 

I tuned a 07 NNBS truck and we turned off his v4 mode and he gets 4 more MPG on the hwy now ahahahaa

 

Probably the tune did it more than ditching the AFM. The OEM's tune for emissions I believe, there is always some power/mileage left on the table. The AFM makes a huge difference on my truck in town, getting 20mpg (us gallons) in the city, 22mpg (us gallons) on the highway. On the highway not so much of a change as I cruise fairly fast but in town its always switching.

A lot depends on how you drive/gearing/style of cab, etc.

 

There is a ton of available adjustment (TPS, RPM, etc) for AFM. I would think that if you were able to get 4 mpg better with a custom tune you would probably be able to pick up a little more by modifying the AFM parameters.

 

hmm... Kinda wish I had gotten my truck tuned by one of you guys with experience on the nnbs trucks. My tuner disabled the afm without even knowing he had messed with it at all. The truck had substantial power gains from the tune, but it started having horrendous gas mileage. Running on stock tune until i can find the time to leave it with him for a couple days so he can play with it a little more.... Sad thing is, my truck is the only way around town, and i cant get anyone to take me to work.... Wish I could get my $350 back.... If one of you guys want to donate a good tune to a guy in need, I will reluctantly accept...

 

Well you don't want mine, I'm just a learner at this point, probably blow something up!!

 

I was wondering that and thinking there has to be some adjustment to the AFM. I thought it would be controlled by load. I could see a substantial increase in mileage with some tunning on the 4cyl mode since it switches back to 8cyl so soon and often. I just need to find a tuner that has some experience with this.