GM’s Gen V LT-series direct-injected engines are packed with high-performance potential. Direct injection gives you better control over the fuel timing, pulling the most efficiency out of every drop of gasoline. The swap world has not been completely taken over by the newest SBC, but it is a real close second to the venerable LS and surpassing it in peak horsepower potential. That doesn’t mean it is perfect, as there are some issues that have cropped up, like a higher rate of lifter failure than its LS counterparts.

Most of the issues with these direct injection engines come from the valvetrain. While GM’s lifters have been spotty at times, it seems the LT has a much higher failure rate than the LS engines, even though they both use the same lifters (standard and DOD). These lifters can fail at any point, even at low mileage. GM has not revised these lifters, and in fact, they doubled-up, going to full DOD (now called Dynamic Fuel Management or DFM) on every cylinder for 2019-up Gen V engines (except LT5 and L8T, which do not have DOD/AFM/DFM).

This is what happens when lifters fail: they twist in the cup and grind the roller wheel and cam lobe to a nub.

While many have come to blame the DOD lifters for all lifter failure, we have found that lifter failure occurs in these engines on both DOD and standard lifters equally. In fact, we have purchased several lifter-failure Gen V engines — three L83s and one L86 — and all four had standard lifter failures; the DOD units were fine. So, what gives? Is the issue in the lifters or something else? These failures are often noted by lifter tick, which is usually blamed on the lifter itself, but this may not always be the case.

Identifying the Root Cause of the Failures

One of the biggest issues for Gen V engines, all direct injection engines really, is oil consumption. LT engines have a very strong PCV system, which draws oil vapor from the valley cover into the intake manifold, to the point that every single LT engine you see has a pool of oil on the bottom of the intake. Newer versions have a built-in catch can, but there are reports of these having issues, too. The problem is that oil vapor sticks to anything that is hot and cooks on it, leaving behind carbon coke. The intake valves tend to gather tons of this gunk, which makes the stems sticky.

The DOD lifters in Gen V engines are the same as every Gen IV LS with DOD/AFM, but the failure rate in Gen Vs is much higher. The cups should stop this, but with enough bounce and side pressure, they fail to secure the lifter.

In port-injection engines, the intake valves are cleaned off by the fuel that washes over them. DI intakes are dry — they don’t have any fuel running over the intake valves — which allows the coke to build. In less than 50,000 miles, the intake valves can have more than 1/8-inch of carbon buildup on the stem. The coke tends to gather near the top of the stem at the guide. This is where the problem starts: the valves get sticky. Back to the lifters for a minute, most of the failures attributed to a lifter failure we have seen involve a twisted lifter, which wipes out the cam lobe and lifter, sending shrapnel through the engine. LTs use the same lifter cups as LS engines, and in normal operation, there isn’t enough room for the lifter to come out of the cup, so what is going on?

A big part of the problem is the carbon coking on the intake valves. These valves came from a 50k L83 Gen V, exhaust on the left, intake on the right. The intake valves had to be hammered out.

Think about how the valvetrain operates. The cam moves the lifters, which raise the pushrods, operating the rockers, which push the valves open. What happens when the valve doesn’t move under load? All that load is now on the lifter roller and cam lobe. All that pressure leads to a weakened lifter cup, eventually stretching beyond its ability to hold the lifter in position. This same event has also caused a number of bent pushrods, which may also play a role in the next version of the story. Let’s flip the script and reverse it. The valve is hanging open, just a little. This allows a little vertical play in the lifter cup, so the lifter can bounce a bit. Over time, this has the same effect, the slight sideload on the lifter stretches the cup just enough to eventually allow the lifter to twist, ending the game. A bent pushrod from a stuck closed valve would have the same loosening effect.

The thing is, these issues are not necessarily constant. As the engine warms up, the carbon gets hot and melts a bit, allowing the valves to move freely, until it cools off and sticks again. In several of the engines we have rebuilt, the exhaust valves fall right out, but the intake valves have often required heavy blows from a soft hammer to get them out of the head. During a cold start, this would be a brutal strain on the valvetrain. A lifter tick that goes away when the engine warms up could be a sign of a stuck valve in a Gen V engine; this should not be ignored.

How To Solve Sticking Valves In GM Gen V Engines

We know there is a problem. What are the solutions? Lifter failure occurs, but it’s not the root cause of the issue. The real issue here is a lack of education that starts with GM not doing its part. Every single dealer should be educating Gen V owners about proper maintenance, but they never do, so we will do it for them. There are two concerns, both of which need to be addressed: intake valve cleaning and oil-vapor capture. It is well documented that all DI engines have higher oil consumption. The Gen V LT engine, on average, burns one quart every 5,000 miles, and some are as high as two quarts. Even seasoned automotive engineers have been surprised to see the “low oil” light pop up between oil changes on these engines.

Installing a proper catch can should be the first thing you do to any Gen V engine. It is critical to stop as much oil vapor as possible from getting into the combustion chamber. Besides the intake valve issue, DI engines do not like burning oil. They can develop Low Speed Preignition (LSPI) from burning calcium, which has been proven to pop the ring lands off the tops of the pistons. DI engines need low-calcium oil, which is why the newest API oil rating, SQ, is an ultra-low calcium formulation. The LT-series PCV system is critical for proper operation, as the 1.0 mm rings need the crankcase to be under vacuum in order to seal to the cylinders. These are low-tension rings, and they just can’t do the job by themselves. This means if you just delete the PCV system, you will get even more blow-by without crankcase vacuum.

Adding a catch can will drastically reduce the oil vapor your Gen V engine burns. The lower port is the PCV valve; the port directly above on the intake is the PCV vacuum side.

The correct routing for a catch can on LT engines is as follows: PCV valve (under throttle body in valley cover) to the catch can, then to the intake vacuum port behind the throttle body. The clean side of the system is the valve cover ports, which are teed to the air intake tube after the MAF sensors (very important!). When the engine is producing vacuum, the PCV system is operational, and the clean-air valve cover ports are the fresh air inlets to the case. This is metered air, so the ECM does not get confused. When the RPM is high enough that the engine stops producing vacuum, the clean air ports go vacuum via the venturi effect, ensuring the crankcase is always under enough vacuum to keep the rings sealed.

We mounted this Holley catch can behind the grille of a 1971 Buick GS, which is powered by a Chevy Performance LT1 crate engine. Having easy access to the can for draining makes it much easier. We drain at every other fill-up.

Getting The Last One Percent

A catch can will get most of the oil vapor, but there will always be some that makes it through. Regardless of having a catch can or not, there is an added maintenance item that should be done every other oil change — an intake valve cleaning. By running a can of intake valve cleaner through the throttle body (NOT in the fuel tank, that doesn’t help), you get clean valve stems that don’t stick. Not only will this reduce valvetrain strain and possibly save your engine from a lifter failure, but it also frees up horsepower. A stuck valve hurts power, even if it is an intermittent issue.

Our first experience with this was in 2016 with a 2015 GMC Sierra Denali powered by the 6.2-liter L86. This truck had 45,000 miles on it when it was purchased, and ran great. We did a test on intake valve cleaners for DI engines, and the results were mind-blowing. The truck gained a lot of power, and the fuel economy went from 14 mpg city and 18 highway to 16 mpg city and 20 mpg highway. It was such a significant change that it made a permanent impression.

Preventing the carbon buildup takes about 5 minutes with every other oil change. A can of GDI intake valve cleaner works wonders and can revive the performance of your DI engine.

This is how things get a bad reputation. Take Dexcool, for example, which GM still uses, but is the most beat-down coolant ever. The problem was a plastic gasket backer that was incompatible with the compounds in Dexcool. They ate the plastic, causing leaks and subsequent overheating and engine failures. All DI engines have this oil consumption and sticky valve issue; they just need an added maintenance item, and all is well.

Are we saying that this is the only cause of the lifter failure issue? Absolutely not, there are inherent issues with these lifters as has been widely documented. The same lifters in essentially the same engine with a different fueling system should have about the same level of failures, but that isn’t the case. The point is that proper maintenance for DI engines is required, and that starts with an intake cleaner every other oil change. It will keep your valves clean, and that keeps the strain off the rest of the parts.