AFM

[duquephart]

Sorry if this has been covered elsewhere/extensively.

 

What have folks noticed in terms of "kick in" speed for AFM? I was in V4 mode yesterday at 25 MPH on a slow moving interstate. It seems like the feature should only come on at a steady rate of highway speed, say 55 and above. Views?

[newdude]

As long as the following parameters are met, it can go into V4 at any time. Really, the most effective points I've noticed for V4 is lower speed town and city driving. 20-50mph is where AFM will run the most from my experience with my 2012 I had. Highway speeds was where it switched in an out the most.

 

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.

 

[Nanotech Environmental]

I like V4 in town. When traffic flow is steady & you hit a bunch of green lights in a row, real time mileage often gets up over 40 mpg.

[scott19677]

I have my AFM tuned out. You can get just as good gas mpg's without it.

 

Just say no to V4. Hittin' on all ?.

[Dnt]

Only reason I would want to set the AFM to only come on at a higher speed would be if I installed a dual exhaust system. To me the exhaust note change V8 to V4 and vice versa is annoying with a louder than stock exhaust system at low speeds (very noticeable). The only handheld tuner that I can vouch for to do that with, is a Max Energy HyperTech 2.0 part 2000. Probably some others out there that will do the same thing?.

[Thomcat]

I like V4 in town. When traffic flow is steady & you hit a bunch of green lights in a row, real time mileage often gets up over 40 mpg.

.02 And my "engine killer" DIC tells me real time I'm getting 99 mpg in V4 coasting downhill, same lying DIC that told me I didn't need a first oil change until 10K+ miles!

 

Only way to get this heavy hunk of metal with the aerodynamics of a brick powered by a 2.6l V4 pumping an additional 4 dead cylinders to get a sustained greater than 40 mpg on a 10 mile trip, with no traffic lights, is to drive it off a 10 mile high cliff.

 

My AFM doesn't bother me so I don't bother it.

[newdude]

.02 And my "engine killer" DIC tells me real time I'm getting 99 mpg in V4 coasting downhill, same lying DIC that told me I didn't need a first oil change until 10K+ miles!

 

Only way to get this heavy hunk of metal with the aerodynamics of a brick powered by a 2.6l V4 pumping an additional 4 dead cylinders to get a sustained greater than 40 mpg on a 10 mile trip, with no traffic lights, is to drive it off a 10 mile high cliff.

 

My AFM doesn't bother me so I don't bother it.

 

 

Funny you mention aero. Take a Camaro or Corvette for a spin with the auto trans. They will drive for miles in V4. Before my brother tuned his car, it was active. I could go a big majority of my 15 mile commute in V4. Same for the 2009 Impala SS he had before that.

 

The car applications are the best example of how AFM can work.

[RyanbabZ71]

 

 

Funny you mention aero. Take a Camaro or Corvette for a spin with the auto trans. They will drive for miles in V4. Before my brother tuned his car, it was active. I could go a big majority of my 15 mile commute in V4. Same for the 2009 Impala SS he had before that.

 

The car applications are the best example of how AFM can work.

Did it save him any gas? I found AFM to have zero effect on mpg on my camaro after I tuned min out

 

 

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[Nanotech Environmental]

.02 And my "engine killer" DIC tells me real time I'm getting 99 mpg in V4 coasting downhill, same lying DIC that told me I didn't need a first oil change until 10K+ miles!

 

Only way to get this heavy hunk of metal with the aerodynamics of a brick powered by a 2.6l V4 pumping an additional 4 dead cylinders to get a sustained greater than 40 mpg on a 10 mile trip, with no traffic lights, is to drive it off a 10 mile high cliff.

 

My AFM doesn't bother me so I don't bother it.

Whatever works for ya. Mine often gets up there for a few miles at a time on flat ground when speeds are low.

 

10k miles on an oil change is fine, if using a decent synthetic. I went that far a couple times on my 06, as the OLM allowed it. It only has a 6 liter capacity, vs 8 on these new ones. I'd have no issue going 10k miles on my 17, if the OLM allowed it. As it stands my first change will be at around 7500 miles or so, going by the OLM.

[Thomcat]

 

 

Funny you mention aero. Take a Camaro or Corvette for a spin with the auto trans. They will drive for miles in V4. Before my brother tuned his car, it was active. I could go a big majority of my 15 mile commute in V4. Same for the 2009 Impala SS he had before that.

 

The car applications are the best example of how AFM can work.

Agreed, logical that a high hp/wt ratio in an aerodynamic vehicle, AFM should have a greater V4 dwell time and greater gas saving potential than a much lower hp/wt brick shaped truck. I'd bet that if you remove the bed, spare tire, rear doors, rear fenders, rear seats, and use a 90 lb driver a Silvy will spend more time in V4 and get better mileage too.

[Orlando8]

I receintly had a GM Borla cat back exhaust installed. Since the install it seems the AFM kicks in more often and seems to stay on longer??

It doesnt bother me in the least as I usually dont even notice it kicking in or out

[Ex-volt]

My 2015 Lt Z71 double cab 4x4, would run in v4 mode up to 75 mph on flat terrain and no headwinds. The DIC over a 100 mile average read nearly 23 mpg. Only mod was a soft tonneau cover.

 

Personally, I like AFM and would have no reason to deactivate it.

[Dnt]

I receintly had a GM Borla cat back exhaust installed. Since the install it seems the AFM kicks in more often and seems to stay on longer??

It doesnt bother me in the least as I usually dont even notice it kicking in or out

Do not know if you are running a 6.2 or 5.3 or if it would make any difference. All I know is that on a 6.2 8 spd with the GM Borla Catback the exhaust note change was very noticeable to me at low speed where it was not before the exhaust. Not saying it was a BAD noise it just made you well aware of when the V4 kicked in. Heck some people might like it that way. On the amount that the AFM stays on I will say that this 2017 6.2 8spd (more or less identical to the 2016 6.2 8spd) the V4 will kick in and stay in at interstate speeds and stay in even on slight upgrades. Might have a lot to do with the huge amount of torque that the 6.2 has I don't know. The smaller engines might have to have V8 more frequently to keep the rubber band wound tight.......

[Orlando8]

Mine is the 5.3

[batman53201]

I get 22mpg average on the highway with AFM disabled.