How General Motors’ Dynamic Fuel Management Works: Video
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Delphi’s Dynamic Skip Fire, or Dynamic Fuel Management in General Motors lingo, will make its production debut in the 2019 Chevrolet Silverado and 2019 GMC Sierra. The system can cut up to seven cylinders in real time to provide a healthy boost to fuel economy in the bot trucks’ V8 engines.
How does this intricate system work? Engineering Explained tackled the technology in a recent video to, well, explain how it works.
The system works by closing off the intake and exhaust valves, and each individual cylinder sports a locking pin. The pin acts as a hinge to control Dynamic Fuel Management.
In regular operation, the engine’s camshaft rotates and presses down on a deactivation arm that opens up the intake and exhaust valve. All the while, oil pressure keeps the aforementioned locking pin in place.
Now, when it’s time to deactivate one or more cylinders, the system determines which aren’t needed and which must be fired to maintain engine balance and the power. Once determined, and this is happening on the fly, oil pressure will press the locking pin back and it will no longer hold the deactivation arm. Thus, as the camshaft rotates, the valve isn’t activated and the cylinder won’t fire. It’s all much clearer in the video graphics.
The system won’t make smaller engines as efficient as larger engines, however. In GM’s 5.3-liter and 6.2-liter V8 engines, drivers may see fuel economy gains from 5 to 20 percent from the previous trucks equipped with the engines. And that doesn’t account for any weight loss or aerodynamic improvements in the 2019 Silverado and Sierra.
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Eagerly awaiting to see what the difference between the 2018’s and 2019’s are for mileage with the 5.3 and 6.2 engines and whatever the base V6 will be. I’m anticipating a 2 MPG bump but with the way the EPA keeps making the figures lower and more strict it will probably be only 1 MPG difference.
I’m not a physicist nor an engineer, but when I think of trying to move a piston with both valves closed, I see air going from “positive pressure” to “negative pressure” inside that cylinder in which I would think would induce a lot of drag on the engine. Think of taking a bicycle pump and blocking both intake and exhaust openings and then try to pump it. On the cylinder that’s deactivated, why not leave the exhaust valve open so air can freely move in and out of that cylinder? Wouldn’t that reduce the ‘compression/suction’ effect that you might get when you keep both valves closed? Of course the engine would have to be designed where the open valve wouldn’t hit the piston at TDC.
Also, in a cylinder that’s deactivated and both valves are closed, as the piston is moving downward (creating low pressure), wouldn’t that also ‘suck’ oil up between the rings that could fowl your inactive spark plugs over time?
I apologize if this seems like a stupid question, but I’ve never heard of anyone addressing this. What am I missing?
Doesn’t the engine need that gas inside deactivated cylinders to act as a spring pushing the piston down? Something has to push the piston down if there is no combustion otherwise 4 other cylinders would do the work of 8 creating an unbalance along the shaft.
That’s how I interpret this technology. Correct me if I’m wrong.
Good question! But wouldn’t compressing that gas in the deactivated cylinder take the energy away from the engine? I know from a basic auto shop class that I had in high school that after removing all the spark plugs, it took less energy to spin the crankshaft on an engine. I’m just not up on how closing all the valves in the deactivated cylinder would be more efficient than leaving the exhaust valve open (or a way for air to enter and exit the chamber freely). If it’s because it’s needed to keeping the engine balanced, is the long-term net gain really worth it? I remember the headaches of the late 1970’s when GM tried something like this before with their V8 engines and it was eventually discontinued. I always thought this approach more as a bandaid holdover until a more fuel efficient engine is developed.
I did a 8 to 4 cylinder downsize on a 1970 Buick Special engine and the loss of power was overwhelming and by closing the valves on the 4 cylinders by using staimless steel clamps the oil galleys could move the oil around and threw the system{changed it back due to giving the Buicl to my dad to drive frowm the country to a small town in the 70’S
Does the system know to shut off the injector from the skip fire cylinder and not deliver fuel to it. Also what happens when the locking pin malfunctions like other oil pressure operated devices such as the timing belt tensioner. Is that going to be a high dollar repair?
My ’09 Silverado with 5.3L engine has this or an older version, on the road I have gotten up to 24mpg, and has worked flawlessly. Much better than the F350 it replaced that got 12mpg.
I love this new technology and this is the type of innovation that will need to be embraced by the masses if we the customers want to continue having high horsepower v8 engines around.
But I am sure somebody will complain about it
As long as it’s reliable and works fairly seamlessly what’s to complain about?
I know nothing about engines and how they work. I do know that I got a brand new Chevy Silverado 4X4 as a loaner a few years ago when my vehicle was in for some warranty work, and the cylinder deactivation in it’s current form left me with a horrible impression. You could ‘feel’ the engine going to half the cylinders and back and when it was running on fewer cylinders there was a tactile ‘coarseness’ to the drivetrain going down the highway. When the engine demanded all cylinders the coarseness went away…..
I am guessing this will turn into a warranty cluster-hump of complaints…. but I hope I am wrong. Remember Chevy’s first gen of 5.2 cylinder deactivation? Didn’t they have a ton of oil burners? Does GM ever perfect anything *BEFORE* sending it out the door for it’s maiden voyage?
Toddsta, I had an ’09 Silverado w/5.3L engine w/AFM. I bought the truck new and had it til last year. The AFM was seamless and and unnoticeable. There were problems with it originally, but GM has fixed them by ’10 model year.
Today, it’s a reliable and proven technology. The fuel savings are not huge, but some is better than nothing especially taking in account how inexpensively it’s accomplished.
YEA what that guy said!
No it does Not! The system is seemless. It smooth and effortless. You can’t even tell weather the engine is in v8 mode or v4 mode unless you look at the dash light.
You are just a person trying to spread lies about this technology!
Brian – you sound unhinged. It is always a mistake to derive your sense of self worth from the vehicle you drive. It will be *ok*…….
This was my experience: I don’t spread ‘lies’…. so please find a safe place and don’t spread your butthurt feelings in public.
Please dont tell me what to Do!
I will give you this: even though you act like a girly-boy…. you are polite and did ask ‘please.’ But I still deny your request.
Dude your a fool!
LOL now that we are over that I have to chime in and say that out of 30-35 rental vehicles over the years with the 5.3 and AFM and even some Dodge Rams with the Hemi that also deactivate cylinders most of these were virtually seamless in operation. Going into 4 cylinder mode was like the transmission going into lockup and you really needed to pay close attention to know when it happened. I also know guys with 200K on these engines with no issues whatsoever.
Good to know guys – the ‘seamless’ part wasn’t my experience with a brand new loaner off the lot…. this would have been in 2013. It had a noticeable ‘shudder/roughness’ on the highway when it hunted and dumped to 4 cylinders. I could feel it in my shoes through what felt like a paper-thin floorboard.
But… if they can do it and it works and isn’t obtrusive – that is great and I am all for it…. gotta be RELIABLE too.
Glad I was able to provide some comic relief…. Hope Brian was able to get the knot out of his panties…. or, keeping with his knack for grammatical errors: ‘get the *not* out of his pantys’ lol
I just don’t like you spreading lies about GM products! I don’t use this site as a attempt to right term papers!
Let us see pictures of your gmc Brian. I want to see how happy you are with your purchase. This looks like a fix to use the old 5.3 housings.From AFM to DFM? ANYONE who has worked on these know that turning off cylinders comes with a cost.
Brian – thank goodness you aren’t using this platform to write term papers…. with the amount of grammatical errors you employ, you would definitely score a failing grade.
GM can suck it…. they put out junk and price it higher than competitive products so that still can achieve their top dollar after they tag on their never-ending incentives and so-called rebates…..
Mark my words: GM is on it’s way to another bankruptcy….. they are borrowing money faster than they can pay it back again. Bloated company that cannot keep it’s fingers off the credit card. We never should have bailed them out the first time.
Just ordered my first Ford with a 5.0 Coyote V8……. has NO cylinder deactivation, presto-changeo sliding camshafts and mechanical complexities at all…. and it still ties GM’s clusterhump 5.3 for mileage ratings….. AND, it smokes it in performance. 395 HP and 400 ft lbs of torque.
Where can I get my Calvin peeing on a bowtie decal ????
Yea, it’s not a term paper! That’s why I dont bother worrying about it! This is not supposed to be a formal place to write!
Please go to the competition and leave us GM people alone!
Mark my words: GM is on it’s way to another bankruptcy…..
…. aaaand Ford is selling 900k trucks these days yet they’ve lost 40%+ of their value. Their credit dropped to one notch above junk status and they’re losing money in Europe and China.
For the deactivated pistons, why are they not generating huge pumping losses by drawing a strong vacuum on their intake stroke when the valves are closed? Also compressing air on the exhaust stroke when the valves are closed?
Been several years since I checked back on this thread….
My F150 with 5.0 v8 has been great.
Meanwhile I have a friend with a 2021 Silverado that had to have all of one side of his intake valves and lifters replaced…under warranty, thank goodness.
My mechanic buddy (certified GM mechanic) says that GM has had this issue with lifters and valves for YEARS and has never addressed nor fixed the problem….says they put them out with soft camshafts too. He routinely places lifters and valves and has no idea why GM hasn’t corrected the cause over the years….I can tell you why, though: because GM doesn’t care…. After 2 Lemon Lawsuits with them over the years (won both), I have written them off.
Anybody here having these issues on the newer Gen 5.3 v8’s?