Active Fuel Management
Posting Guru
Joined: Feb 2004
Posts: 1,388
Likes: 0
From: Saratoga, NY
like i said, i don't know how it works, just that it does.
the old 4-6-8 caddy system when working properly would increase fuel mileage on the highway by 5-6 mpg. and that was pretty impressive on a car that would only get 12-13 mpg when running on all 8.
unfortunately, the 4-6-8 system sucked, and broke more than it worked.
the old 4-6-8 caddy system when working properly would increase fuel mileage on the highway by 5-6 mpg. and that was pretty impressive on a car that would only get 12-13 mpg when running on all 8.
unfortunately, the 4-6-8 system sucked, and broke more than it worked.
Cargo Master
Joined: Apr 2003
Posts: 3,476
Likes: 224
From: Frequently frozen MN
I think that small turbo engines like the Ecoboost work better, so the variable displacement deal is probably dying off. It probably provides some mileage increase by idling cylinders when the load is light, but it still has to move all of that mass.
As for the Caddy Cheerleader, this is the first time that I've seen anything positive about it as well. I think that most of them were modified to remove the variable displacement feature -- which, as noted by others, was unreliable.
Besides just failing, I read that it was sensitive to electrical noise. A noisy traffic signal could apparently knock it out.
hj
As for the Caddy Cheerleader, this is the first time that I've seen anything positive about it as well. I think that most of them were modified to remove the variable displacement feature -- which, as noted by others, was unreliable.
Besides just failing, I read that it was sensitive to electrical noise. A noisy traffic signal could apparently knock it out.
hj
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
It's not dying off.
It works on the principal of reducing pumping losses. It requires energy to pump air into the cylinders, and it also requires more energy to pull air past a barely open throttle valve than a more open throttle valve (say when cruising at low throttle).
AFM/MDS/Whatever works by physically disabling the valve train on certain cylinders. In Chrysler's MDS, it disables 4 cylinders. The valves stay closed on those dead holes, effectively turning those cylinders into air springs.
Doing that pretty much eliminates the pumping losses associated with those cylinders. However, since now you only have half the cylinders working, this means you need to open the throttle up a lot more, which further reduces pumping losses since it is easier to pull air through an open throttle.
It works on the principal of reducing pumping losses. It requires energy to pump air into the cylinders, and it also requires more energy to pull air past a barely open throttle valve than a more open throttle valve (say when cruising at low throttle).
AFM/MDS/Whatever works by physically disabling the valve train on certain cylinders. In Chrysler's MDS, it disables 4 cylinders. The valves stay closed on those dead holes, effectively turning those cylinders into air springs.
Doing that pretty much eliminates the pumping losses associated with those cylinders. However, since now you only have half the cylinders working, this means you need to open the throttle up a lot more, which further reduces pumping losses since it is easier to pull air through an open throttle.
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