GM V8's

[daka]

I read somewhere that the engines in the GM SUV's do an 8 6 4 "thing" depending on the power needed, True? What year does this start ? Problems?
Thanks

 

[nc6600]

I read somewhere that the engines in the GM SUV's do an 8 6 4 "thing" depending on the power needed, True? What year does this start ? Problems?
Thanks

Yes the 5.3L and maybe 6.0L??? have a thing called active fuel management(AFM) which switches from 8 to 4 cylinders when power isnt needed. It started in 07 and is still being used in Tahoe,Yukon,Suburban,Avalanche,Silverado,and sierra vehicles.

 

[Nnaboy]

No it doesn't have problems, good innovation by GM!

 

[Repo503]

This was first introduced on the now 1981 Cadillac Fleetwood. It worked....once or twice before it had to be taken into the shop for a fix. Today it works seemlessly in a number of cars. Ive driven Benz V12 - before the twin turbos that have this. In our trucks you cant even really tell unless youre paying a lot of attention.

A side note...in the movie Casino Sam "Ace" Rothstein (Robert Deniro) is the victim of a car bomb in his Cadillac V 8-6-4.

 

[GMTech48]

ti's called "DOD" displacment on demand...and it switches from 8 to 4 active cyls....no 6 cyl. mode as the old Caddys had

 

[wmgood64]

chrysler 300c also have this

 

[daka]

OK, I remember that it was problematic back then.., so now its OK...!!
I'll probably just look for an 06.

 

[73shark]

The 8-6-4 Caddy system as I remember was pretty much all mechanical. It was fraught w/ problems. Kind of like GM's small block diesels were.

 

[daka]

So, now it's OK?
The early Cadi one was a disaster, as was the cobbled together diesel...
No problems with the new ones (yet)?

 

[fco_gonzo]

Straight from GM:

Active Fuel Management Technology
--------------------------------------------------------------------------------

With Active Fuel Management technology from GM, the Vortec 5.3L V8 engine standard in LS 4x4 models and all LT and LTZ models as well as the Vortec 6.0L V8 engine in Tahoe Hybrid power when you need it, and you get the efficiency of four cylinders when you don't.

In situations where extra power is not needed, such as cruising down the highway on level roads, Active Fuel Management deactivates four of the eight cylinders with seamless precision.
When load demands increase, such as when the vehicle accelerates or travels uphill, valves are reactivated to provide eight-cylinder operation.
The bottom line: the Vortec 5.3L V8 and 6.0L V8 engines are more efficient in providing the energy to move the vehicle when only four of the eight cylinders are operating.
The powerful 32-bit engine control computer triggers cylinder deactivation based on inputs from vehicle sensors — making deactivation almost undetectable.
Active Fuel Management technology helps the 2009 Tahoe Hybrid 2WD equipped with the Vortec 6.0L V8 engine offer an EPA estimated MPG 21 city, 22 highway.
In addition, exhaust-noise silencing measures and powertrain mounts add to the engine's overall smoothness.

 

[73shark]

Mine works fine but I disagree w/ the statement "cruising down the highway on level roads". Mine will not go into V4 mode on a level road unless speed is about 55 or less. Somehow I don't consider that cruising. Now some w/ 4.10 gears say theirs does better than that.

 

[RyanbabZ71]

Mine will not go into V4 mode on a level road unless speed is about 55 or less.

I have had mine in V4 at 65 mph quite a few times. Once you hit any kind of incline it goes into V8

 

[07SuburbanLTZ]

I find mine to be in 4 cyl mode a lot.

 

[nc6600]

I find mine to be in 4 cyl mode a lot.

same.

 

[convoyduel]

I monitor mine pretty closely and run in V4 a lot of the time. The two things that help the most are keeping your foot easy on the accelerator and having the transmission in tow/haul mode. It locks the torque converter for longer intervals and helps keep it in V4 above 45 unless you are on a good hill or grade.

If I keep my odometer in V4/V8 mode and maintain a light to moderate acceleration, I typically get between 19.3 and 20.4 overall mileage as montiored by computer and hand calculations. When I don't care (i.e. when gas gets real cheap), I average around 16.2 to 17.5 overall.

You can barely feel when the system kicks on. There is an ever so slight change in feel to the engine. I wouldn't call it a shudder, but you do feel it if you're paying attention.

 

[rsinsel]

OK, I remember that it was problematic back then.., so now its OK...!!
I'll probably just look for an 06.

The advent of electronic throttle control really solved most of the issues that plagued the system used back in the eighties. I can NEVER tell when I am in v4 mode. I do wish I could make custom changes to the engines ECM so that I could get more v4 mode out of it. It does work. I am getting 20-22 out of it so far on the highway and about 16 in the city. No a/c yet. I figure I should still get sticker MPG or better. Lets hope so.

 

[Gambler]

You can hear when you are in V4 mode, it gets deeper and it seems to vibrate slightly more.

 

[rsinsel]

Mine works fine but I disagree w/ the statement "cruising down the highway on level roads". Mine will not go into V4 mode on a level road unless speed is about 55 or less. Somehow I don't consider that cruising. Now some w/ 4.10 gears say theirs does better than that.

I have heard the same argument that the 4.10's work with it better. It may be on more, but they are burning more gas the rest of the time. I would NEVER buy 4.10's for economy, but for towing. And if you are towing, MPG is not your concern nor are you going to get it. I think this is a myth that needs busting. Mine cruises right along at 65-75 happily going in and out of v4 mode. I have the 3.08 gears.