LS lifter failure: causes and fixes

Common causes (any hydraulic-lifter LS):

• Low oil level or pressure: the lifter doesn't pump up fully, leaves a gap and ticks. This is the most common cause.
• Worn or failing lifters.
• Aerated oil: from hard driving or an overfilled crankcase whipping air into the oil.
• Bent pushrods or damaged rockers.

AFM (Active Fuel Management) engines add their own failure mode: AFM uses oil-pressure-controlled lifters to deactivate cylinders. A failing AFM lifter can show up as a single-cylinder misfire, a persistent tick, a rough idle, low power and a cylinder-specific misfire code. It can progress to bent pushrods, a worn cam lobe and metal in the oil.

Fixes:

1. Check and change the oil at the correct level and grade; that alone can quiet a marginal lifter.
2. Pull the valve covers and look for bent pushrods or damaged rockers.
3. Replace failed lifters before they wipe the cam or send debris through the engine.
4. On AFM engines, a proper AFM delete means a non-AFM cam, all 16 lifters (not just the 8 AFM ones), new lifter trays, and blocking the AFM oil circuit. Plugging the passages while keeping AFM lifters is not a delete. The computer also has to be retuned. See the making power guide and tuning.