Faced with increasingly stringent federal efficiency mandates, automakers have employed a host fuel saving measures in recent years. Technologies like direct injection, automatic stop/start, and variable valve timing have all been developed in pursuit of fuel economy improvements, but some of these features have side effects that can compromise a vehicle’s drivability and create maintenance issues down the road.

“The OEMs are constantly under the gun to improve fuel economy to meet these rising standards,” says Michael Litsch, Sr. Product Manager for domestic tuning at Holley Performance Brands. “But at the same time, some of these automakers want to put V8s in their trucks, SUVs, and muscle cars. So they’re looking everywhere they can to save a bit a fuel here and there. And in an effort to try and meet those standards with these big-displacement engines, in the mid-2000s GM and Chrysler developed systems that would mechanically deactivate cylinders in the engine during light-load driving scenarios, like during steady-state highway cruising and other situations like that.”

Features like General Motors’ Active Fuel Management (AFM) and Chrysler’s Multi-Displacement System (MDS) can disable four of the engine’s eight cylinders under these light-load conditions, while GM’s newer Dynamic Fuel Management (DFM) system can deactivate up to six cylinders at a time.

“It’s enough power to maintain that cruising speed. And at a glance, the concept seems sound – if you’re only running on half of the engine’s cylinders, you’re probably using half of the fuel, right? But it doesn’t work that way,” Litsch says. “Power output is a function of burning fuel, and you’re not burning a ton of fuel to maintain a constant highway speed on eight cylinders. And because you’ve dropped down from eight to four cylinders, you generally have to burn a little more fuel in each of those four cylinders in order to maintain the required amount of torque to keep the vehicle moving. So it’s ultimately not as beneficial as it might seem on the surface. But you’d never know that as an owner because these displacement on demand systems are enabled by default, so you never actually see what the fuel economy would be under normal driving conditions without the system operating. It almost seems like something that was designed to address specific testing methods rather than real-world use cases.”

To add insult to injury, these systems are also known to create drivability compromises as well.

“For example, when you’re operating on four cylinders and you suddenly need all eight cylinders again for passing power or some other reason, there’s a transition that occurs. And no matter how sophisticated the design of the system is, that transition is going to take a tangible amount of time,” he tells us.

“So you’re cruising along and you give it some throttle to pass another vehicle or go up a hill, there is going to be a delay in that throttle response as the system brings those disabled cylinders back to life. If you jump on throttle and the first that happens is the engine says, ‘hey, wait, hang on a second while I get everything figured out,’ it degrades the driving experience. But again, most folks don’t realize that’s what is happening because they’ve never had an opportunity to drive the vehicle without that feature enabled.”

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These cylinder deactivation systems can also create issues for folks who’ve installed an aftermarket exhaust system on their vehicle. “The factory exhaust system on any vehicle that’s equipped with cylinder deactivation technology is engineered to not sound weird when the tech shuts those cylinders off,” he says. “The problem is that if you decide to upgrade your exhaust system, the aftermarket systems are designed to sound good when the engine is operating on all eight cylinders. But when those cylinders are deactivated, an aftermarket system is going make the engine sound awful. That’s actually one of the main reasons that people seek out a way to disable these cylinder deactivation technologies.”

But the most egregious issue created by these displacement on demand systems is that, over time, they can actually cause serious mechanical damage to the engine itself.

Prone To Failure By Design

In cylinder deactivation systems like AFM and MDS, the ECU controls electrically operated solenoids that regulate the flow of engine oil to specially-designed lifters. When the ECU determines that cylinders can be deactivated, these solenoids open, allowing oil to flow into the lifters and triggering them to collapse. This process inevitably creates additional wear and tear as compared to an engine without cylinder deactivation technology.

“Part of the problem is that these lifters are constantly being activated and deactivated, and what we’ve noticed is that it’s the lifters that get disabled are actually the ones which tend to fail prematurely,” Litsch explains. “The solenoids can begin fail over time as well.”

He says that a ticking sound coming from the top end of the engine is a telltale sign that a lifter is failing, and if the issue is ignored, it can turn into a major headache.

GM Active Fuel Management lifter.

“A few different things can happen when a lifter fails – the most common result is that causes the roller that rides on the camshaft to fail. That roller is full of needle bearings, and if it comes apart, those needle bearings can make their way into a cylinder and cause all sorts of havoc. And if they make their way past the piston, it can even take out the bottom end of the engine. Another problem that’s more common with the Chrysler MDS technology is that the lifter will actually turn in the bore. If that happens, you have this roller that’s supposed to be sitting flat on the camshaft but now it isn’t. And that will cause the roller to grind into the camshaft and destroy the cam. At that point the engine will likely be non-functional.”

Litsch says that these problems are most prevalent in GM trucks from the mid-to-late 2000s mainly because they’re the oldest vehicles that are equipped with this technology, but he’s quick to point out that these issues are so commonplace, it may be just a matter of time before it happens to any vehicle that has a cylinder deactivation system.

AFM systems can be found on many 2007 to 2018 model year GM vehicles that are equipped with a 5.3-liter or 6.2-liter V8, while the more advanced DFM system is equipped on a number of 2019-and-newer GM vehicles that are equipped with the 5.3-liter or 6.2-liter V8. MDS, meanwhile, is commonly found on 2005-and-newer Mopars like the Chrysler 300, Dodge Challenger and Charger, Jeep Grand Cherokee, and Ram 1500 models that are equipped with either the 5.7-liter or 6.4-liter Hemi V8. Vehicles with factory-installed manual transmissions typically are not equipped with cylinder deactivation tech.

What You Can Do

Litsch notes that there are two common ways to put the kibosh on these cylinder deactivation systems.

“Displacement on demand ‘delete kits’ have become incredibly popular for obvious reasons. A basic kit is going to consist of a stock factory camshaft for that specific engine, a set of factory lifters that were designed for vehicles that aren’t equipped with this deactivation tech, and all of the gaskets and fasteners you’ll need to put it all back together. And most outfits that offer these kits will also offer upgrades – things like performance camshafts, better gaskets and fasteners, and so on. And the popular kits out there generally also include some kind of tuning solution because the engine won’t run correctly until it’s been tuned to account for the absence of the AFM, DFM, or MDS system.”

He says that these kits typically cost between $1,000 and $2,000, depending on the options and upgrades chosen. However, if the problem is addressed early enough in a vehicle’s lifespan, a delete kit may not be necessary.

“Generally speaking, I’d recommend going with a delete kit for any higher-mileage vehicle just to be safe – anything with more than 50,000 miles on the odometer. But the important thing to remember is that the sooner you disable the system, the longer those parts are going to last. If you ignore it, the valvetrain may eat itself up as early as 75,000 miles. But if you disable it on day one, the chances are you’re going to get 100,000 miles or more out of the valvetrain.”

And disabling – rather than deleting – a cylinder deactivation system is a much less expensive proposition.

“Tuning is necessary if you’re installing a delete kit, but it’s important to remember that you can also simply disable a cylinder deactivation system with a tuner. And if you disable it with a tuner early enough, mileage-wise, it can prevent a lot of these problems down the road while also fixing the throttle response and exhaust note issues that we discussed earlier.”

In addition to their performance prowess, DiabloSport tuning solutions like the Pulsar, Predator X, inTune i3, and Trinity 2 all offer the ability to disable these cylinder deactivation systems with ease.

“Literally all you have to do is just flip one switch in the tuning software,” says Litsch. “And at that point the ECU no longer thinks that it has that cylinder deactivation system, so the engine runs on eight cylinders all of the time. At the end of the day, you’re going to need a means of turning off this cylinder deactivation system in the ECU whether or not you decide to delete kit or simply disable it. And these tuners offer the easiest ways to do that.”

For owners of AFM-equipped GM vehicles who just want all eight cylinders all of the time, the Range Technology AFM/DFM Disabler and DiabloSport Sprint AFM Module are an easy way to stay in full power mode while also deactivating its Auto Start/Stop system. Simply plug the disabler into the OBD-II port, and it begins working immediately, with no trace left behind when removed. Compatible with most V6 and V8 GM cars, trucks, and SUVs—including 5.3L/6.2L 10-speed applications—it does not support 2022.5+ Refresh model trucks or 2021+ SUVs. Owners of these later trucks can employ a Range DFM Module that plugs into the vehicle’s ECM.

Video: See how the Range Technology AFM/DFM Disabler works here.

These cylinder deactivation systems are a great example of OEM’s paying more attention to regulations like CAFE standards that to the pocketbooks of their customers. Hopefully we’ve armed you with some solutions to help you get the most out of your truck.