Any of you guys noticing the cars going into 4cyl mode? I can feel a vibration or buzzing at cruise when the DOD becomes active. Its kinda annoying.

On a side note she is getting great mileage.. We are up to 17.5 with mostly city driving! Maybe I'll have to live wtih DOD :wall:

17.5 is great?

17.5 is great?

That's city driving. A lot of sixes won't do better. And the engine is still new, tight and not broken in. That's good mileage under that scenario. On the highway, 25 mpg + should be attainable.

I'd love to see 17.5......got 12.5 on the last tank in my trailblazer ss, haha

17.5 is great?


Hell yes that good for a 361HP car!! :patriot:

And no. My car is as smooth as a baby's butt. I still haven't been able to tell when it kicks in or out.

no vibration for me, however I have been running the AC, does DoD work with the ac on?

no vibration for me, however I have been running the AC, does DoD work with the ac on?
Same here. Can't feel it at all. The AC seems to default to "ON" so I just hit the off button. I think AFM does work in AC.

Any of you guys noticing the cars going into 4cyl mode? I can feel a vibration or buzzing at cruise when the DOD becomes active. Its kinda annoying.

Alvin - I felt it too on my test drive, I agree it was annoying , but I did not drive enough to see how annoying it was, and I was purposely trying to get it to go into DOD mode. Also I found that at idle the engine would stumble a little every minute or so.

Same here. Can't feel it at all. The AC seems to default to "ON" so I just hit the off button. I think AFM does work in AC.r.penguin - congratulations on your car, I did not know you got it.

That's city driving. A lot of sixes won't do better. And the engine is still new, tight and not broken in. That's good mileage under that scenario. On the highway, 25 mpg + should be attainable.

:thumbsup: Yep!

Also I found that at idle the engine would stumble a little every minute or so.



That's the horsepower gettin antsy :gears:

But in all seriousness. My '99 Chevy Silverado 2500 4x4 6 liter does the exact same thing at idle.

The 4V mode only activates at road speed under light load conditions. It idles in 8V mode. I have another post somewhere on this board that lists the conditions and computer checks for the 4V/8V decision.

Ask your service department for Service Information Document # 1959166 for way more information on it than you'll want to read.

That's the horsepower gettin antsy :gears:

But in all seriousness. My '99 Chevy Silverado 2500 4x4 6 liter does the exact same thing at idle.thanks, I wonder why?

thanks, I wonder why?

I don't know either, but my wife's 04 Escalade ESV does the same thing.

Chip

GTO does also.

Thanks to all for letting me know it is common in the GM V8's.

Any of you guys noticing the cars going into 4cyl mode? I can feel a vibration or buzzing at cruise when the DOD becomes active. Its kinda annoying.

On a side note she is getting great mileage.. We are up to 17.5 with mostly city driving! Maybe I'll have to live wtih DOD :wall:

Ah, so that's what that was. I thought it was just some weird harmonics in the exhaust at ~68mph.

I could hear it really well with the rear windows cracked for airflow.

I was kind of shocked that they'd let harmonics like that get through testing at a fairly normal highway speed...but now it makes sense.:o

I can feel the vibration also. For me it is between 55mph and 68mph.

It is annoying if I pay attention to it.

So we are fairly certain its the AFM?

Cylinder Deactivation

For those of you who have your GT's already:
What Is your impression of this feature?

Especially in this scenario:

Your cruising along the highway, half the cylinders are
Deactivated, however your quickly approaching a slow
Moving truck. You hit the gas, preparing to make a pass:

What happens? Is there a delay between the cylinders firing back to life?
Or does it respond adequately? On my test drive I didn't have
The chance to do this since I didn't want to beat on the car.

If there is a prolonged "hesitation" how bad is it before everything starts
To roar?

I havent noticed it at all. I dont do much freeway driving but i am sure it has been enough to have noticed if there was or not.

Cylinder Deactivation

You hit the gas, preparing to make a pass:

What happens? Is there a delay between the cylinders firing back to life?
Or does it respond adequately? On my test drive I didn't have
The chance to do this since I didn't want to beat on the car.

If there is a prolonged "hesitation" how bad is it before everything starts
To roar?

I have posted a lot of info on the AFM elsewhere on this forum, but the short answer is, it takes 250 milliseconds to activate and all 8 cylinders are hitting in 2 crank revolutions which is faster than you'd notice.

Ask your service manager to print out Service Information Document ID# 1959166 and there's more than you want to know about AFM. :)

The transistion appears seemless. It happens so fast you dont know your in it until you recognize a slight vibration. When you mash the gas, the only delay I can recognize is the transmission downshift.

I remember the 300c Hemi that I test drove for an hour which also has a similar system. I didn't notice the DoD kicking in at all while I was cruising at a constant speed. I'm expecting the G8 GT to act the same way but we'll see.

Cylinder Deactivation

For those of you who have your GT's already:
What Is your impression of this feature?

Especially in this scenario:

Your cruising along the highway, half the cylinders are
Deactivated, however your quickly approaching a slow
Moving truck. You hit the gas, preparing to make a pass:

What happens? Is there a delay between the cylinders firing back to life?
Or does it respond adequately? On my test drive I didn't have
The chance to do this since I didn't want to beat on the car.

If there is a prolonged "hesitation" how bad is it before everything starts
To roar?

I don't have a GT, but I do have a Grand Prix GXP with the same AFM feature in an LSx motor (LS4 in my case) with 34,000 miles under my belt. As said before, it is transparent. The tranny kickdown takes the longest. The AFM is off before the throttle is even wide open.

Chip

Cylinder Deactivation

For those of you who have your GT's already:
What Is your impression of this feature?

Especially in this scenario:

Your cruising along the highway, half the cylinders are
Deactivated, however your quickly approaching a slow
Moving truck. You hit the gas, preparing to make a pass:

What happens? Is there a delay between the cylinders firing back to life?
Or does it respond adequately? On my test drive I didn't have
The chance to do this since I didn't want to beat on the car.

If there is a prolonged "hesitation" how bad is it before everything starts
To roar?

Well, on my test drive the car took way too long IMO to downshift, but it has nothing to do with AFM. It's due to a very reluctant and slow downshifting automatic transmission. It's about 3 seconds between mashing the gas pedal and the engine responding. There's so much of a pause that you get a big old school front to back weight transfer that reminded me of my 1972 Buick LeSabre - no joke. It's the one thing that's making me seriously question whether I should buy this car.

I remember the 300c Hemi that I test drove for an hour which also has a similar system. I didn't notice the DoD kicking in at all while I was cruising at a constant speed. I'm expecting the G8 GT to act the same way but we'll see.

I've driven a 300C for about 30 minutes (a family members) and I couldn't tell when DoD was working. I also found that transmission pretty satisfying despite only having 5 cogs. Fairly quick to downshift and decent upshifts too.

.........It's due to a very reluctant and slow downshifting automatic transmission. It's about 3 seconds between mashing the gas pedal and the engine responding. ........

Its not quite that bad, but it does feel like it.

17.5 is great?

Sounds great to me, for being a 361hp 4,000 pound car that is not even broken in yet!

You already beat EPA!

With Flowmasters I can hear the switch over in tone/pitch around that 65 to 69 mph...of the 4 cyl mode...its just a differnt sound..4 cyls going through the flows..than all 8.I get passed by everyone in cali..going 65 but i get over 25mpg in 4 cyl mode on a flat road and no wind....so its worth it when im going distance....there is NO hesistation ..to get back into 8 cyl mode, when you push the loud pedal down to pass . the only way i can describe it.is ...is passing with a VEngence..you go from 60 to 90 in just a few seconds...if you floor it....to properly pass someone.you just give it alil roll into the throttle and the torque keeps u going forward with no problem...regarding the guy looking at 335 and the G8....the 335 is a great car ....my dad has the 08 convertable.but he paid over 55k for it for his wife....hes retired 7 figures deep...i am not.and the extra 10 to 15K for the reg. 335 is not worth it to me...just to have a BMW name plate...the G8 is 99 percent as luxurious....just as quick.easy to mod and actually work on...try working on a 335 .bi turbo ( good luck) and the sound of the G8 with open exhause it much better than a 335.

I felt a little something thru the shifter. My biggest complaint is the 1st to second shift in manual mode. Its very lazy going in, has anyone else had that problem. I drove two cars and they both did it, this one was the worst. Other then that its an awsome car, I had a choice of grey, white and red. The red war for me, however, the white really looked good too.
locrzn

About the lazy shifts

Back in 1996 GM has introduced a technology called Torque Management. In 2003 they refined it to the point it is at today. The lazy shifts you call them are due to this.

Torque Management has 2 modes, Abuse Mode and Shift Mode.

IIRC, Abuse mode kicks in at WOT, less than 5 MPH (and some RPM factor as well as any speed that requires a downshift into first). Ignition Timing Advance is pulled well below zero degrees (I think it was -12 degrees...I made charts with AutoTAP that I can upload). Once the speed and rpm thresholds are SLOWLY exceeded, Ignition Timing is allowed to advance to well over 24 degrees. This is why GM vehicles are dead off the line.

Once above 3500 rpm, ignition advance is slowly pulled as the vehicle accelerates still at WOT (Wide Open Throttle). Around 500 RPM before the the upshift, ignition timing is pulled by huge amounts, the upshift is made, then before full ignition advance is allowed, the vehicle accelerates another 500 rpm, but until that point, ignition advance is still held back.

Now you know why the vehicles always feel dead just before and slightly after shifts instead of immediate as well as poor off the line performance and throttle response. Instead of building the transmission to handle the power, horsepower is limited by the computer. Transmission protection!

A proper tune will remove these problems and yield immediate response, but since the 6L80-E transmission has a separate computer inside, mail order tunes become slightly more complex, but not impossible. A local speed-shop with a dyno and "skills" can do a tune that will bring up fuel mileage up to 12% (depending on air density in the area you live) and HP 9% depending on type of fuel chosen for the tune.

^ Great post.

Instead of building the transmission to handle the power, horsepower is limited by the computer. Transmission protection!

This explains that slip when I pulled out in the G8 V6. Did GM do all this to save money on transmissions?

It is because of this "transmission protection feature" that I might pass on the G8 altogether.

Torque Management is on all GM vehicles, the more powerful ones make it obvious though. Been this way since 1996.

vhato...great info.....you point out in laymens terms what we have all be experinceing ..but sounds like this is a solvable problem with the correct tuner
i know vector motorsports is hard at work on solvin this....
any others you might know of?
where u or are u an engineer by trade?

.....
where u or are u an engineer by trade?

Nah, I am an IT Admin by profession (and a Sheriff's Deputy when I am ordered to the road by a captain), which doesn't qualify me at all.
Back in my early days I owned two Nissan 300ZX Turbo's. All my buddies were on my butt about trading and getting a Chevy truck with the mighty 350. So I did and it was turd slow. I owned several trucks including a 2000 model I lifted to the sky. Well I was always broke ($$$$) so I decided to buy tools instead of mechanics time. The 2000 Z71 needed gears bad, and it was $1200 for just the rear and I didn'tknow what ratio to get so I learned to dothem myself and have done several for lots of people (front and rear).

Next I wanted to tackle the ECM. A close friend modded a 2002 Camaro SS SLP (Runs 10's now and is street legal..all engine). He paid a well respected online speed shop to dyno tune his car after a cam swap. These guys have a huge reputation, but don't know $hit about tuning a car beyond the basics of a stock engine....his would not idle. So he asked for my help (I am a computer dude..but that was just a misconception that I had tuning skills) We purchased AutoTAP, EFILive and HPTuners for his car and truck and my 2 trucks and I studied my butt off. I fixed his Volumetric Efficiency Table allowing his car to idle and drive at all speeds not just WOT. From there I learned more about GM OBD2 vehicles than I would have EVER imagined.

There are alot of misconceptions about fuel injection and mass air-flow that just about everyone including myself believed but until you start tuning yourself you wont know.

A cool thing we in the US don't have, but I learned from tuning is a technology called "Lean Cruise". It will take your AFR from 14.7 to 16-17 AFR by leaning out your fuel mixture at specified speeds like 60 MPH allowing even greater increases in Fuel Economy. It is disabled by GM for North American vehicles due to EPA regulations, but our buddies in Australia get to have it.

Other things are separate driving habit shift modes. Slow easy shifts for cruising, and aggressive firm shifts at WOT....if you enable them.

Buy a used laptop, HPTuners, Wide Band O2 sensors and a GTech Pro (sure it isn't balls accurate, but it does help you measure changes in performance as you begin to tune). Live on LS1tech.com and you can have fun to.

A cool thing we in the US don't have, but I learned from tuning is a technology called "Lean Cruise". It will take your AFR from 14.7 to 16-17 AFR by leaning out your fuel mixture at specified speeds like 60 MPH allowing even greater increases in Fuel Economy. It is disabled by GM for North American vehicles due to EPA regulations, but our buddies in Australia get to have it.

What does the EPA have against Americans conserving fuel? BTW, what does AFR stand for? And what is the significance of 14.7 to 17 AFR?

AFR stands for Air/Fuel ratio. The target is 14.7:1

The EPA isn't against us making our engines more fuel efficient, they are however attempting to control NOx output from our exhaust pipes. This is what makes enabling Lean Cruise illegal in the US.

Alot of work must go into making Lean Cruise work anyway. As the AFR is raised to 15-16:1 the EGT (Exhaust Gas Temperature) increases so to lower the temperatures the ECM richens the fuel mixture which defeats the purpose unless every part of Lean Cruise is tuned.

I've actually felt the characteristic vibration as low as 25mph around base and as high as 75mph on a downhill stretch. It's not bad, it's just kind of there if you're looking for it. Once you know what it is, you actually look for it so you know you're saving gas.

I've posted a video as a demo of how the system works. The system is always in V8 mode at idle and speeds below 25 mph. Above 25 if cruising it shuts 4 off or while coasting. When watching the video take note of the speed in relation to the All Active vs Half Active. This was done by putting the car in Engineering mode by holding down the left nob on the steering wheel while starting the car.

http://www.youtube.com/watch?v=hV7wvmNyQAI

I've posted a video as a demo of how the system works. The system is always in V8 mode at idle and speeds below 25 mph. Above 25 if cruising it shuts 4 off or while coasting. When watching the video take note of the speed in relation to the All Active vs Half Active. This was done by putting the car in Engineering mode by holding down the left nob on the steering wheel while starting the car.

http://www.youtube.com/watch?v=hV7wvmNyQAI

Do you have an educated guess as to how fast the G8 can cruise before having to use all 8 cylinders to combat wind?

I'll do some further investigating on this. I keep forgetting to put it in Eng mode when I start the car on every day driving. LOL I usually think of it when i'm on the highway when it's not a good idea to shut off the car and start it again at 70 haha...

Any of you guys noticing the cars going into 4cyl mode? I can feel a vibration or buzzing at cruise when the DOD becomes active. Its kinda annoying.

On a side note she is getting great mileage.. We are up to 17.5 with mostly city driving! Maybe I'll have to live wtih DOD :wall:


My G8 GT is #677 of 888 so it was built close to yours and I can't really notice when AFM / DOD kicks in or out. No vibration or telltale noise at all.

I've got 12K miles and getting 19.8 MPG, according to the DIC, combined with about 70% highway miles.

I hate the vibration. Deal with it every morning on my way to work. It almost sounds like I have my back window cracked, and it stumbles every day when I pull into the lot at work.
Is there anything open for this, or is it just how it is? I am taking the car in today to get the winter tires/wheels put on and to have the paint checked out to since I have a few chips that I noticed when I first got it.
Dave

Do you have an educated guess as to how fast the G8 can cruise before having to use all 8 cylinders to combat wind?

Yes, the AFM is determined by engine vacuum, so if the PCM sees the engine working too hard it activates all cylinders. On level highway, little wind, its about 72 mph or so.

I can feel the vibration, probably more than others, since I've tweaked the AFM settings so I can cruise between 75-80 mph with AFM active. I have gotten 25-26 mpg consistently on the highway at those speeds, and my average is usually around 20-21 mpg.

I had Vector turn off DoD. I'm getting about 17.5 mpg in the city. No highway results
because I haven't went on any kind of trip. And my car only has 843 miles on it.

I find that using premium in my car reduces the vibration from AFM/DOD when in 4 cyl mode.

I find that using premium in my car reduces the vibration from AFM/DOD when in 4 cyl mode.

+1
and DOD works up to 80 mph

I feel it more when the convertor locks up at 35-50 mph range then smooths out as revs rise, but never a bother. I use it at times to judge gas pedal pressure when driving around town actually, Seeing now an average of close to 20 city.

But the on ramp to the local parkway seems to negate that every other day when I commute :) Love to ring it out every so often. Kinda nice being one of the bigger dogs on the highway when it comes to power and passing :)

I hate the vibration. Deal with it every morning on my way to work. It almost sounds like I have my back window cracked, and it stumbles every day when I pull into the lot at work.
Is there anything open for this, or is it just how it is? I am taking the car in today to get the winter tires/wheels put on and to have the paint checked out to since I have a few chips that I noticed when I first got it.
Dave

Isn't AFM disabled in the Sport mode for the transmission? Maybe you should drive in Sport mode and that will eliminate the vibration. For the extra fuel economy, I've learned to deal with it.

Isn't AFM disabled in the Sport mode for the transmission? Maybe you should drive in Sport mode and that will eliminate the vibration. For the extra fuel economy, I've learned to deal with it.

Anyone have the answer to this question? .... I couldn't find it anywere :confused:

It is NOT disabled in sport mode. I have seen it go into AFM while in sport mode.

It worked in Sport mode for me yesterday.

It's disabled in "manual" mode but is active in Sport mode.

It's disabled in "manual" mode but is active in Sport mode.Correct.

I am new to the forum just learning.

jawilsn: That is neat "Engineering mode" and the video is great.
jcar: How do I find out what number car mine is?

It's disabled in "manual" mode but is active in Sport mode.

Yup, my bad. I never drive in Sport mode, so I got that part confused. Tried Sport mode on the way to work yesterday and I could definitely still feel the vibration. On the plus side, I really like the way the tranny shifts in Sport mode! Now that gas prices have come down, I'll probably drive in Sport mode now (sacrifice an mpg or two for the better shift points).

I have started noticing a ping type noise when it goes from 4 to 8. Anyone else ?

I have 11,500 miles on it.

I can definitely feel it when it goes into an out of AFM, its quite noticeable when I' m pushing it to the limit right before it switches off. And I always seem to get an average of 16.5-17mpg in daily driving to work which is 50% local roads/50% highway. I've never been able to get great gas mileage.

I have started noticing a ping type noise when it goes from 4 to 8. Anyone else ?

I have 11,500 miles on it.

Mine was more like a low bass "studder". I changed mine to only engage in sixth gear with my tune. I got sick of it at low speeds.

let me add i like the way it shifts in sport mode alot better.and i hate the vibration also as little as 35 mph it sucks ,pretty noticable.id rather do without.