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Switching between V4 / V8 mode

DarkSky

Full Member
Joined
Oct 25, 2012
Messages
239
I've noticed the only time my '07 LTZ really drops to V4 mode is when I'm coasting on the city streets without my foot on the gas (basically, when starting to approach a stop of some sort).  Whenever I just -barely- touch the gas, it switches to V8 again.  And when in cruise (in the city at least), the tiniest little grade going up, or even a gust of wind from the front, or going around a bend, puts it back in V8.  Actually, the only time it's not in V8 is basically when i'm coasting to a stop.

Is this normal?  I haven't done much highway driving with it yet, but if I set the cruise at like 110km/hr (~60-63MPH) on the highway for an extended period, will it drop to V4 mode?

So far from what I can tell, this whole cylinder deactivation thing seems more of a gimmick than anything else!

??
 
Yes it's a gimmick. My mileage hasn't changed but maybe even went up when I turned that feature off. Probably better from my plugs staying cleaner. There are a few of us loosing oil because of the lousy AFM.
 
It goes into V4 only when lightly loaded. How long it will stay there at cruise depends on terrain, wind/air resistance, whatever.

For more than a few, AFM has proven to be a malevolent gimmick as it has a tendency to oil foul nos 1 & 7 cyl rings and cause high oil consumption. Much discussion on this board if you care to know more. I shut AFM off...as have others.
 
LornesAV said:
Yes it's a gimmick. My mileage hasn't changed but maybe even went up when I turned that feature off. Probably heing to keep my plugs cleaner. There are a few of us loosing oil because of the lousy AFM.

I did not know that you could turn it off, how do you do that?
 
I thought AFM was 4/6/8 or off at a stop, I don't have it so didn't think about a disable
 
ltxi said:
Handheld or custom tuner.

Is that something that the shop could do?  And secondly, is it *that* much of an issue that I should turn it off?

I can't see it *ever* going in to V4 mode on the highway because the amount of air resistance would always keep in in V8.  On cruise in the city, on a -completely- level (or downhill) road and no bends or curves, mine will stay in V4 mode for awhile.  But the smallest gust of head wind, or going around a bend that makes the tires grip a little harder, and it's back in V8 mode.

I wonder if the criteria can be reprogrammed for when it goes in and out of V4 ?

Like, obviously always in V8 at a stop so it's already in V8 when you accelerate from a stop, but maybe stay in V4 mode when going >40km/hr (20mph?) and the pedal is less than whatever % of throttle.
It would be great to be able to program it for cruise on the highway when you're just pushing against air resistance and the weight of the vehicle doesn't play much part in it anymore.

But even still, I'm not sure it would save any gas.  In V8 mode it still only has to use half the throttle to push against the air resistance that it would in V4 mode...

Oddly enough, my 310HP 5750lb V8 Avalanche doesn't use any more gas than my 275HP 4650lb V6 Envoy did...  I don't seem to be spending any more at the pumps on average.  I was chalking it up to cylinder deactivation up until now :)
 
Dealer or u&c repair shop....no. Use a handheld such as a Predator or have a custom tuner do it.

AFM only becomes an issue if it eventually eats your 1 & 7 piston rings and you start burning oil by the bucketful....and by then it's usually too late. Enough evidence out there that I won't leave it on. But my truck's been tuned since day one, so for me it was simply a matter of deciding to shut it down....no real extra effort or expense.
 
I never received notice of a post to this one so sorry for the delay Z66 Butch. Like Itxi wrote I used a predator and turned it off. They should be fairly cheap now that they have been discontinued and replace by another tuner. www.diablosport.com
 
No problem, I wondered how to turn off the AFM, now I know.
 
I had no idea you could turn that option off. I'll put this on my list of stuff to do as I often felt that it didn't help anyway  (n).


 
My new 2013 Ava has about 500 miles on it. From day one I noticed a vibration and then started to pay more attention to it as it keeps doing it. Took the dealer for a drive and he says it is when the truck shifts from v8 to v4 and put the computer on it and says nothing is showing wrong and nothing he can do. He is correct that it does it when it switches from v8 to v4 and vibrates until I give it gas to switch back to v8. Does it real bad around 56 to 59mph and around 33-38 mph. I can really find a fix or anyone talking about it. It really ticks me off that it is brand new and I have issues. If anyone can help or have a suggestion. My other question is if I did purchase the Diablosport to disable the active fuel management will this solve my problem and can I enable it later??
I appreciate any help, tks Marc
 
Most of the time I could hardly tell it changed to 4 or 8. Yes you can turn in on and off but not on the fly or within a minute.
 
It's completely impossible to tell when mine switches from V8 to V4.  The only way I know is when I have the display set to show what mode the engine is in.  But if I even just barely touch the gas, it pops back to V8 mode.  Basically it only drops to V4 when I take my foot off the gas and coast.
 
Exhaust tone on light throttle. Actually noticed the absence of this as well after I shut it down.
 
I had the problem of not switching to V4 after my 2010 (66,000 mi.) had worked fine. Finally, my dealer talked with the GM guy that designed AFM. The problems develop when the oil pressure on the top end is different from pressure on bottom end. Takes a special guage to check it. He said this is usually caused by wear & leaking from camshaft bearing. Mine was replaced under warrantee and works great and will save fuel if you drive reasonable. #active fuel management
 
Gents,

I have a 2011 Ava with 19,000 on it and I have the stumbling idle at stop and a rough ride when going into 4 cylinders during city driving say up to 40 mph. I believe it has gotten worse since ownership (5000 miles) and overall gas milage has fallen to under 16 mpg. Been to the dealer several times with no service codes. Until I get the AFM tuned off I am driving in the city in the manual mode of 5. It appears to knock out the AFM and keeps it in the 8 cylinder mode and drives and rides 100% better, like when I first bought it. I will monitor the gas milage and I bet it will improve!!
 
I've got a 2011 -
Small noticable difference/feel when switching to/from v4 mode.

Mileage improvement is significant ....
I live in the flat state of florida - so grade isn't usually an issue....

I can run between 50 and 65 and it will stay in v4 mde for miles.....
Fuel improvment is noticable.
Took a trip form south Fla to northeast fla - on return I had haul mode turned on - so it wouldn't switch into afm I ended up with about an 5.6 mpg difference btween the 2 legs of the trip. One way travel was about 320 miles so it was pretty telling....

The biggest difference was when I put bigger tires and custom rims(heavier). I lost overall mileage - and the added weight drag impacted the v4/v8 mode shifts....
 
My question is how much are you paying for this if you have a shop do it? I am going to talk to a local shop here and I am wondering a ballpark idea on price.
 
Wow I always wondered if you could turn it off how much is the predator or programmer. With 90k is it worth turning it off??
 
You can get a good pro tune for half that. Don't know what Diablosport charges for their tuners these days but I doubt it's even close to that much.
 
Talked to the local shop here 150$... Said most of the cost is buying license to unlock computer. Sound right???
 
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