ACTIVE FUEL MANAGEMENT
 

Does anyone have the new Silverado 1500with the ACTIVE FUEL MANAGEMENT where it drops it from 8 down to 4 cyl. I was wondering how it does on gas mileage. Any real world gas mileage would be helpful. Thanks

RE: ACTIVE FUEL MANAGEMENT
 

Dont expect to much improvement around town. Its more for highway driving when you are light on the throttle.

RE: ACTIVE FUEL MANAGEMENT
 

I would agree with enigne2. The only place in town you will really notice a difference is sitting at a stop light due to the stop and go. It should always run all 8 from a dead stop so you have the power to get it moving.

RE: ACTIVE FUEL MANAGEMENT
 

I have both Silverado and Tahoe. Nither works well with AFM. If you are going downhill it will convert to 4 otherwise it flips back and forth between 4 and 8. At times this is noticable on the Silverado.

On the Silverado and on the highway I have to be behind a semi or with a tailwind to have prolonged 4 cylinder benefit. I also feel it should drop to 4 cylinders at a stop light - but it doesn't - go figure -both Tahoe and Silverado rein on 8 cylinders at a traffic light or at idle - at least thats what's on the display.

If you travel at 55MPH or less on cruise control, then this will be a benefit. Otherwise its just a selling point for the car.

RE: ACTIVE FUEL MANAGEMENT
 

What do you suppose would would happen if it "dropped to 4 cylinder mode at a stop light"?

Ever tried uplugging 4 spark plug wires to see how your old V8 would idle when you were a kid?

AFM is engineered to reduce fuel consumption by about 10% - 15% and that is about what it does depending on your driving style.

RE: ACTIVE FUEL MANAGEMENT
 

Not sure what would happen. I am not an engine expert nor do I claim to be one. But simple logic would say "If you can drop to four cylinders while driving, why can't it drop to four cylinders at idle - or possibly 6 cyliders?" I am sure the timing changes for this configuration which could be incorportaed into the design. For me I would rather have the option to turn this off, but I can't. With the Tahoe, it works and is somewhat unnoticable, but in the Silverado, the drive train or something vibrates - it can be annoying.

I am just providng a user opinion from first hand experiecne.

RE: ACTIVE FUEL MANAGEMENT
 

I have a NBS 07 Silverado 1500 Extended Cab 4WD with the 5.3L. The engine is aFlex Fuel model and hasAFM. I am not overly impressed with AFM to be honest. I sold a 2005 Silverado 1500 EC 5.3L(HO)4WD when I bought the 07. The 05 got far superior MPG without AFM. Everything about these trucks is the same, except for the body style obviously, but for the axle ratio and the AFM. Both EC's, both 5.3L's, both 4WD, both ran 265-17 AT's,etc... The 05 had a 3.42 gear ratio and the 07 has 3.73's.

The 05 got the following MPG...

100% City = 14-15
Mixed= 17-20( depended on how much was highway vs city )
100% highway = 21-23( highest was actually 22.7 )

The 07 gets the following MPG( so far hopefully it improves )...

100% city = 15-15.5
Mixed= 16-16.5
100% highway = 17-19( highest to date = 18.9 )

Decent MPG for a full sized 4WD no doubt but very disappointing when a newer truck, with fuel economy improvments, actually gets worse MPG then the truck you sold. GM has touted the MPG improvements in thenew GMT900 Silverado & Sierra big time but so far I am not seeing it.

As to AFM working. I do notice it when it changes mode but it is very smooth. More like going into an extra OD gear when going into V4 and like shifting down when coming abck into V8 mode. The longer you drive the less you notice it. I have not experienced the rough transition other folks have seen.

AFM on my truck does come on pretty easy when cruising along on a flat road with sustained RPM levels and speeds 45 MPH+. Does not stay in very long though. I don't believe in real world applications it is going to do much. In a controlled environment it might help but not much for actual people out on the road driving.

RE: ACTIVE FUEL MANAGEMENT
 

The engine idles at about 600 RPM in V8 mode, if you drop half of the cylinders the engine will not stay running at an idle.
V4 mode is only operational at over 1,000 RPM's and light load conditions for this reason.

RE: ACTIVE FUEL MANAGEMENT
 

Thanks ZX... and I agre with NHSilverado. But hey I love the newtrucks both Tahoe and Silverado.

RE: ACTIVE FUEL MANAGEMENT
 

I just got mine (2007 4x4 silverado5.8 flex-fuel)and drive both city and hwy and have noticed the same thing that NHSilverado has. It kicks on and off quite frequently when dring 55mph but doesn't stay on for long except if your going down hill. It's a pretty smooth transition and I hardly notice it, but I don't really think this has any real benefit.