Active Fuel Management control - Page 2

quote:

ORIGINAL: gdf7279

So why couldn't they make it Idle in V4 mode and jump into V8 mode when you start moving? 

 
You can answer this question by going out and pulling four plug wires off and let 'er idle. 
 
On a more serious note, I've found that using tow mode in town will keep it in V4 mode more and yields better mpg even tho the rpm will be higher (unlocks torque convertor).  I've tried this both ways on the same stretch of road and found it to be true.  A tail wind helps big time. 

when your under 40mph the biggest hurdle that your car has is to get the wheels rolling (think about how heavy your car is and trying to push it yourself vs when your on the hwy the momentum reduces that effect) this is why keeping your tires properly inflated can help so much...after that the wind resistance over takes the rolling resistance of your tires...why do you think they say that its more fuel efficient to use your a/c on the hwy rather than rolling your windows down

also...what do you mean by saying that the Tow/Hual Mode unlocks your torque converter? ive noticed that shifts are much more firm and that it does stay in v4 mode longer but i dot know if it could cause problems in the long run...course i guess we dont know about switching between 8 and 4 cylinders either

Next time you are driving at about 45 or below at a constant speed and tranny has locked up, engage tow mode and watch the tach.  It will increase about 300 rpm.  I assumed that's because the torque convertor is unlocking.
 
I don't think V4 mode is going to hurt anything in the long run as per Dave it quits after ten minutes to allow the engine temp. to equalize.  I'll have to take his word as never had it go that long.  But he also has 4.10 gears which seems to put engine in it's best operating zone.  Others with 4.10 gears usually report better mpg also.

Actually, when you engage T/H at 45 you shift back to 3rd, out of OD.  WIth T/H on, OD will not engage until about 56MPH.  The TC may or may not have been locked up in OD at 45, but will lockup in T/H.  To test this theory, put your shifter in "3" and drive 45 then engage T/H, and your RPM's will stay the same, maybe even decrease if your TC wasn'ta already locked.
 
My experience is the engine seems just a little too weak in the 1700 RPM range so it's close to lugging, which does not equate to the best MPG.  Engage T/H and your RPM's are up around 2000 which seems to be the sweet spot for the best MPG.  (BTW my best highway MPG's are right around 2000 which works out to 60-65MPH.  Yes I get better MPG at roughly 62-65 than I do at 55.  No I don't know why.)

quote:

ORIGINAL: 73shark

quote:

ORIGINAL: gdf7279

So why couldn't they make it Idle in V4 mode and jump into V8 mode when you start moving? 

You can answer this question by going out and pulling four plug wires off and let 'er idle. 

On a more serious note, I've found that using tow mode in town will keep it in V4 mode more and yields better mpg even tho the rpm will be higher (unlocks torque convertor).  I've tried this both ways on the same stretch of road and found it to be true.  A tail wind helps big time. 

 
Doesn't really answer the question does it.  First, I wouldn't presume to even guess which of the 4 cyl. are turned off during V4 mode.  But, on a realistic point for the question, the AFM is designed to put the truck into 4cyl. mode.  So, it makes sense to some of us that the truck should perfectly fine when running in V4 mode, so why not idle.  I don't claim to be an expert in anything, that's why I ask.
 
With the tow mode, I noticed the same thing as you.  Have you actually confirmed that in the long run it is better in Tow mode?  I notice that when doing down hill in Tow Mode seems to be less efficient than standard.  I'm guessing that it probably depends on the driving conditions whether Tow Mode or Regular is better.

It wouldn't idle well in V4.  You will have severe vibration due to the unpowered 4 Cyl causing an out of balance situation.  The example given was to pull 4 plug wires while the veh was idling.
 
They already took measures to reduce the vibration when in V4 mode. but you willl still feel it in the pedal etc. when at speed.

Cylinders 1-4-6-7 are the ones the are deactivated.

To put it simply;
One factor is:
When half of the cylinders are deactivated the engine has a much narrower operational range of efficiency due to the fact that (unlike a normal 4 cylinder motor) there is still a fair amount of resistance and pump loss to overcome from the dead cylinders, if the RPM's drop too low (>1,000) the engine will lug easily and either stall or stumble, keep in mind that you're still dealing with a V8 engine here not a 4 cylinder.

Another factor is that these AFM equipped motors are attached to much larger transmissions than a normal 4 cylinder vehicle is, these big tranny's absorb quite a bit of energy when Drive is selected at idle.

I realize that this is difficult for some to understand but the software program that operates the AFM system will enable 4 cylinder deactivation any time that it will improve fuel efficiency with almost no exceptions.

I have 600 miles on my Tahoe. I haven't tried cruise yet, learning something new everyday. So far gas mileage has been poor. I do notice a difference between 2 and 4 wheel though. I stay in two wheel most times.

Welcome to the Tahoe forum.  As Dave always says, only use Auto or 4WD when on slippery surfaces.  Saves gas and wear and tear on the drive train.

Hey Thanks. My jeep had the part time option. Four high/low. No full time option (auto). I believe it's safe to drive in auto year round, but of course would be foolish gas wise. But, it's the four high, and of course four low that are only used when needed. I could be wrong.

What is the CD for a Z71 tahoe with the "un" aerodynamic front end bumper and shrouds?

.38

quote:

ORIGINAL: ZX1100F1
Cylinders 1-4-6-7 are the ones the are deactivated.

To put it simply;
One factor is:
When half of the cylinders are deactivated the engine has a much narrower operational range of efficiency due to the fact that (unlike a normal 4 cylinder motor) there is still a fair amount of resistance and pump loss to overcome from the dead cylinders, if the RPM's drop too low (>1,000) the engine will lug easily and either stall or stumble, keep in mind that you're still dealing with a V8 engine here not a 4 cylinder.

Another factor is that these AFM equipped motors are attached to much larger transmissions than a normal 4 cylinder vehicle is, these big tranny's absorb quite a bit of energy when Drive is selected at idle.

I realize that this is difficult for some to understand but the software program that operates the AFM system will enable 4 cylinder deactivation any time that it will improve fuel efficiency with almost no exceptions.

 
This is the best answer I've heard.  It makes sense to me.  I was keeping an eye on my Tac. today and noticed that it when slowing down it jumps back to V8 mode between 500 and 1000 RPM. 

quote:

ORIGINAL: fredster

Actually, when you engage T/H at 45 you shift back to 3rd, out of OD.  WIth T/H on, OD will not engage until about 56MPH.  The TC may or may not have been locked up in OD at 45, but will lockup in T/H.  To test this theory, put your shifter in "3" and drive 45 then engage T/H, and your RPM's will stay the same, maybe even decrease if your TC wasn'ta already locked.

 
You're correct.  The reason I thought it was the TC lockup was because if you put it in "3", it will take it out of V4 mode even if you're going downhill.  Not sure I understand why but that's the way mine works.

And opposite of logic, the firmer, harder shifts that occur when in T/H are actually better for the transmission.  A long, smooth shift is actually much harder on the trans.

That's cuz the long smooth shifts are achieved by slowly engaging the clutches which allows some slippage.