I agree with that. But when I induce mine to V4 on slight grades at 35-45 mph, I see 3-5 mpg improvement on the DIC. This is in town running on the same area in both modes. I don't know at what speed that improvement would go away at cuz I've never been able to get V4 above that. But I have the dreaded 3:73 gears. Have a trip coming up to Omaha, so maybe can do some more experiments.

Just curious as to what this is:

 

The AFM system will only allow 4-cylinder mode to stay engaged for 10 minutes and then it will switch it back to V8 mode for a short period of time to allow the internal engine components a chance to normalize temperatures.



I also agree that when 4-cylinder mode activates you should see a noticeable improvement in the MPG shown on the DIC however even though you may be going up an incline the computer will only allow this to happen during low-load operations, the computer doesn't know what the road is doing only what kind of load is placed on the power plant, if it's running in V8 mode it's because the loads are too great to benefit from being in 4-cylinder mode.

There are many variables that effect the AFM operation, such as road grade, condition, surface type, tire rolling resistance, wind speed and direction, vehicle weight, fuel type and quality, outside air temperature, engine temperature and the list goes on.


In simple terms the AFM computer is calibrated in a manner so that if 4-cylinder mode would provide a benefit then it will select 4-cylinder mode otherwise it fires all 8.

 

Thanks for the info. I think you may have answered this before but does the computer randomly (more or less) select the four cylinders to deactivate? I suspect it does for wear reasons.

 

Always shuts down the same four cylinders (cylinders 1, 4, 6 and 7) there is no extra wear imposed on the always-on cylinders as most all wear is a result of friction from rotating mass and not a result of the power stroke.

 

i thank god i dont worry to much about that whole mpg thing, as long as i keep selling alot of chinckens . ohh sorry selling chickens because i own a small chain of flame broiled chicken resaturants.

 

Dave,
I found this very surprising, actually very shocking. I have always thought it was random. Strangely enough when Dodge put this technology in the Hemi in 2006 they said the V4 mode would always randomly shut off cylinders to avoid specific cylinder wear. Now this was forum talk,I never had the MDS hemi, my last was a 2005. But I swore I read/heard this many times that it was random or other wise it would cause cylinder wear issues.

I take your word on the 5.3 using the same ones with no issues, however does the dodge function differently?

 

The Diamler/Chrysler MDS system found on the Hemi always shuts off the same 4 cylinders as well and has operated this way since it's introduction.

 

Thanks for the clarification Dave!

 

In fact Chrysler cuts out the same 4 cylinders as GM's AFM system, MDS is basically an exact copy of GM's DOD (now called AFM) system that was launched in the 5.3L equipped 2005 Trailblazer/Envoy.

 

I think the whole thing is pointless. Just a gimmick to appease the environuts out there. My single cab 02 with 5.3 averaged a little over 21mpg driving to California.