Chevrolet LY5

The 5.3-litre truck V8 of GM's Gen IV small-block era — one member of the LS (Gen IV small block) family and a continuation of the LS architecture, pushrod rather than overhead-cam, and the engine under the majority of full-size GM trucks and SUVs of the period.

Active Fuel Management is the fault line. The system shuts down four cylinders under light load by collapsing their lifters, and the collapsible lifters are the part that fails: a failed AFM lifter produces a persistent misfire on one cylinder, and in the worst case damages the camshaft lobe beneath it. A misfire on an AFM engine that appears only under certain load conditions, or that moves, is worth suspecting here before ignition or fuel.

The same system is behind the family's oil-consumption reputation — the AFM pressure-relief valve sprays oil at the piston skirts, and a fouled cylinder can follow. A truck of this era burning oil with no external leak is a known pattern, not a mystery.