I can't believe how often the trans goes into V4 mode and a such a slow speed. I would like to break in the car in V8 mode, but the only was is to paddle shift. Any suggestions. Car has only 120 miles on it.

 

I think it'll only go into V4 mode in ECO or Tour mode. Choose another setting. I think that should do it.

 

How do you tell if it is in V4 or V8 mode? I do not hear any difference nor do I see any indicator reflecting which mode it is in.

 

That is inaccurate information. With the auto transmission, it will go into V4 in any of the modes. The only way it will not go into V4, is if you have the transmission selector set to M and you paddle shift.

TDY - If you scroll through the display options, there is an option to see fuel economy data and the V4 and V8 icon will appear with it to indicate which mode it is in.

 

Navigate through the menu using the steering wheel button and u will see the indicator 4/8 mode.

 

C7s with A6 (2014) and A8 (2015+) automatic transmissions will switch between 4 and 8 cylinders in all driving modes unless you are paddle shifting. M7 will only switch to 4 cylinders in ECO mode. There is a display in the INFO display tree that shows V8 in yellow and V4 in green. This display is similar in Tour, Sport, and Track display modes.

Ron

 

Correct me if I'm wrong but the ENGINE switches between V4 and V8 mode. JK about correcting me.

 

Yep, use paddle shift with an automatic and take a few long rides on some back roads and get past 500 miles!

Agree with your idea of breaking it in in V8 mode. Also using various rpm's and some deceleration engine braking. That is why I would use more back roads and less interstate.

Did that with my M7 and cruised in 4th, 5th and 6th and changed about every 10 minutes. Frankly in 2 3/4 years I have only used ECO a few times to see how much better the gas mileage was. It was not much! I drive in Sport 95% of the time.

 

Does anyone know which 4 cylinders are deactivated in v4 mode?

 

The four that aren't active.

 

Well that's more info than anyone else has produced so far...💡

 

If I remember correctly its 3,4,5,6... The middle two on each side.

 

Yep, found a neat video animation that shows this clearly:

 

Talk about asking for the time of day and the answer starting off with "how to make a watch," copied this info!

Note, I took out ~half of this description, thought most eyes would roll with this much! It does answer the question-I put in Bold!

Here goes:

Cylinder Deactivation
All that you wanted to know (and more) about the AFM system.

"To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1, 7, 6, and 4, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

Manifold absolute pressure (MAP) and the conditions listed below determine when cylinder deactivation is enabled.

•Engine has been running for greater than 30 s
•Engine speed is between 700 and 2800 rpm
•Engine oil pressure is between 187–455 kPa (27–66 psi)
•Engine coolant temperature is between 40–129°C (100–264°F)
•Engine oil temperature is between 16–128°C (61–263°F)
•Throttle angle is 6% or less
•Ignition voltage is greater than 11 V
•Transmission is not in first, second, or reverse gear
•Vehicle speed is greater than 25 kph (15.5 mph)
•Brake booster pressure is greater than 42.0 kPa (6 psi)
•Vehicle is not in fuel shut of mode
•Vehicle is not in heater performance mode??
•Vehicle is not in tip in bump acceleration mode??
•Vehicle is not in oil aeration mode??
•Vehicle is not in low range (if equipped)
When cylinder deactivation is commanded, the ECM will determine what cylinder is firing and begin deactivation on the next closest deactivated cylinder in firing order sequence. For example, if cylinder number 1 is on its combustion event when cylinder deactivation is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when cylinder deactivation is commanded ON, then the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing.

The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, when all cylinders are active, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When cylinder deactivation is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One valve lifter oil manifold assembly solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each cylinder deactivation lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the valve lifter oil manifold assembly, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event. During an intake event, the intake cam lobe is pushing the valve lifter upwards to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve. However, when cylinder deactivation is commanded ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately, and deactivate the exhaust valve.

By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge, or exhaust gas charge, in the combustion chamber. The capture of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when operating in V4 mode cylinder deactivation mode.

During the transition from V8 to V4 mode, the Fuel Injectors will be turned OFF on the deactivated cylinders. To help prevent spark plug fouling, the ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met and maintained for cylinder deactivation operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, then return to V8 mode for 1 minute.

Switching between V8 and V4 modes is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the valve lifter oil manifold assembly solenoids to energize, and the time for the valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

To help control contamination to the hydraulic circuits, a small replaceable oil screen is located in the valve lifter oil manifold assembly oil inlet passage, below the oil pressure sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.

During service, use extreme care in keeping the valve lifter oil manifold assembly free of any contamination or foreign material.

Cylinder deactivation may be inhibited for many reasons including the following:

•Engine coolant temperature out of range for cylinder activation
•Engine vacuum out of range
•Brake booster vacuum out of range
•Transmission gear incorrect or shift in progress
•Accelerator pedal out of range or rate of pedal application to fast
•Engine oil pressure and temperature out of range
•Engine speed out of range
•Vehicle speed out of range
•Minimum time in V8 mode not met
•Maximum V4 mode time exceeded
•Decel fuel cutoff is active
•Reduced engine power is active
•Torque management is active
•Catalytic converter over temperature protection is active
•Piston protection is active, knock detected
•Cylinder deactivation solenoid driver circuit faults
 

Switching between V8 and V4 modes is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator.”

There is a good deal more information about how oil pressure is controlled to activate the lifters, that I left out for simplicity."
Note this is the authors comment not mine-I took out other "stuff."

 

I noticed we have 2 different reports on which cylinders are deactivated. I'm not sure which is correct. I've always thought the middle 4 were deactivated but have no evidence either way. Anyone have definitive proof? Inquiring minds want to know.


with supporting video by Olden Slowe

 

Interesting difference and why is the video wrong!!
Page 9-603 of the 2014 Service Manual says they are cylinders: 1, 4, 6, 7.
Page 9-418 says they are 1, 7, 6, 4 (for what ever reason stated in different sequence.)

Then the cylinder numbers, as expected are left bank, starting 1 in front, 3, 5, 7. On the right bank starting with 2 in front, 4, 6, 8.
The firing order is 1, 8, 4, 3, 6, 5, 7, 2.
Note I put the ones that deactivate in RED. Makes sense, skip in even order!

If the center pairs that would make the firing: 1, 8, 4, 3, 6, 5, 7, 2! That sure would run rough!

 

If it will go into V4 mode in all modes, then what is the ECO mode for?

 

I don't think that its a problem during break in if it was thay would program it out for the first 500 miles

 

OK, I found supporting documentation for the 1, 7, 6, 4 cylinders as the ones being deactivated. Cool. However, the documentation reveals the firing order has changed to 1, 8, 7, 2, 6, 5, 4, 3 like the LS engines. The result is the same, as far as AFM is concerned. Source is the 2015 owner's manual. Who'd a thunk. Pays to read the "book of words".

 

Funny I picked up the firing order from a LS source that said the
LT1 was the same. Can't believe everything because it's in print!

But as you say, still the same issue, if the 4 center cylinders were deactivated that would have a big miss! Swapping the #7 and #2 firing sequence does not change that the center cylinders are not the ones. Still funny the video is wrong.