Active Fuel Managment

[dpmcclary]

Just curious--why is my 2007 GMC Sierra 5.3L with Active Fuel Management using all 8 cylinders when idling?

 

I assume this is normal but would intuitively think only 4 cylinders are needed when idling. Educate me please.

 

Dave

[bbb]

8 cyl idles smoother...and its 0 mpg no matter how many cyls.

[Ocean Guy]

I would also think it should idle at 4. Yes, 8 is smoother and it is 0 miles per gallon , but how many minutes per gallon?. Using 8 instead of 4 during idling will consume more. Isn't the idea behind active fuel management to save the fuel?

[VMax2007]

I would also think it should idle at 4. Yes, 8 is smoother and it is 0 miles per gallon , but how many minutes per gallon?. Using 8 instead of 4 during idling will consume more. Isn't the idea behind active fuel management to save the fuel?

 

 

It has 100% to do with engine performance at idle. Imagine all of the whining we would be hearing if GM utilized V4 mode at idle and the engine idled rough? Also, it may have to with oil pressure at idle since the special lifters utilize hydraulic pressure to activate. Trust me, GM Engineers had their reasons.

[Erik F]

Why not six then?

[grimmysnr]

/threadjack

 

How do you know if you have AFM? This is DoD right? My dealership said my truck didnt come with it and its a 5.3.

 

/endthreadjack

[z85violator]

i dont think 06's have afm. right?

[grimmysnr]

Doesnt appear so according to this

 

The technology was introduced as displacement on demand in the 2005 model year Vortec 5300 V-8-equipped Chevrolet TrailBlazer EXT and GMC Envoy XL and Envoy XUV. It is available in the 2006 model year 5.3-liter V-8-equipped Buick Rainier; Chevrolet TrailBlazer, TrailBlazer EXT, Impala SS, Monte Carlo SS; GMC Envoy and Envoy XL; Pontiac Grand Prix GXP; and Saab 9-7X.

[Paul58]

I want to know if there's a way to hack the computer and force it to run on 4 cyls more than it does now? I love seeing between 25-30 mpg in V4 mode cruising down the highway, but even the slightest bump in the road kicks it back into V8 mode! It just seems way more sensitive than it could be...

[VMax2007]

I want to know if there's a way to hack the computer and force it to run on 4 cyls more than it does now? I love seeing between 25-30 mpg in V4 mode cruising down the highway, but even the slightest bump in the road kicks it back into V8 mode! It just seems way more sensitive than it could be...

 

I have heard the tuners can make the AFM use V4 mode more often. You will want to verify this when you talk to your tuning guy.

[spartus]

I want to know if there's a way to hack the computer and force it to run on 4 cyls more than it does now? I love seeing between 25-30 mpg in V4 mode cruising down the highway, but even the slightest bump in the road kicks it back into V8 mode! It just seems way more sensitive than it could be...

 

I have heard the tuners can make the AFM use V4 mode more often. You will want to verify this when you talk to your tuning guy.

 

 

 

 

http://forum.efilive.com/showthread.php?t=...p;highlight=dod

 

EFI LIVE now has the option... If your tuner uses EFI live, you are in luck.

[Paul58]

I want to know if there's a way to hack the computer and force it to run on 4 cyls more than it does now? I love seeing between 25-30 mpg in V4 mode cruising down the highway, but even the slightest bump in the road kicks it back into V8 mode! It just seems way more sensitive than it could be...

 

I have heard the tuners can make the AFM use V4 mode more often. You will want to verify this when you talk to your tuning guy.

 

 

 

 

http://forum.efilive.com/showthread.php?t=...p;highlight=dod

 

EFI LIVE now has the option... If your tuner uses EFI live, you are in luck.

 

 

Well, I don't have a tuner at the moment, but am in the market for one. I see wait4me mentioned in that thread, do they sell that tuner?

[Fyrcaptain]

Paul, there is supposed to be a PCM update at the dealer that addresses the AFM.

Might want to see if it pertains to your VIN

[ken1mod]

Gentlemen,

 

About idling or running on 6. Very rough. the engine will not fire evenly and will have a powerful torque vibration. ie, it will not fire a constant number of degrees apart. In 1981 Caddy had this same concept of deactivating cylinders. it worked but it had a v 6 mode that the engine would rarely run in. It was so rough that it killed the concept for 25 years. This engine was silk smooth in either 4 or 8 cylinder mode but shook in the v6 mode.

 

Ken

[svaiskau]

I was under the impression that it idles in V8 so there is no power loss waiting to change out of V4 when you give it gas off the line.