Chevrolet Gen IV small block (4.8–7.0 LS)

General Motors' fourth-generation small-block V8 — the LS2, LS3 and LS7 in the Corvette, Camaro, G8, Commodore and Caprice, and the truck engines LY2, LY6 and L76 across the GMT900 range. The 5.3 of that range — the LY5 and its LH6, LC9 and LMG siblings — has its own page. Its successor is the LT (Gen V small block) and its predecessor the LS (Gen III small block).

What separates it from the Gen III is cylinder deactivation, and that is where its faults live. Active Fuel Management shuts down four cylinders under light load using collapsible lifters, and those lifters fail — producing a persistent misfire on one cylinder and, if it is left alone, a wiped camshaft lobe beneath it. A load-dependent or wandering misfire on one of these is AFM until proven otherwise. The same system sprays oil at the cylinder walls, and a truck burning oil with no external leak is a pattern rather than a mystery.

The LS7 has a defect of its own and it is the serious one: valve guide wear. The guides wear, the valve stem then does not seat squarely, and a dropped valve destroys the engine. It is specific to that engine and worth a leak-down test on any car carrying one, regardless of how it is running.

And the LS4 is the odd one out — mounted transversely, driving the front wheels in the Impala SS, Monte Carlo SS, Grand Prix GXP and LaCrosse Super. Its accessory drive, exhaust and transmission share nothing with the rest of the family, so a procedure written for a rear-drive LS does not describe it.

L98 on a Holden is this engine; on a 1980s Corvette it is not. GM used the designation twice, twenty years apart — the earlier one is a first-generation 5.7 with tuned-port injection.

⚑ It is a family spanning 4.8 to 7.0 litres, and this catalogue carries it across twenty-one models at 4.8, 5.3, 6.0, 6.2 and 7.0. A figure quoted for the Gen IV LS names one member: the truck 4.8 and the LS7 share an architecture and almost no parts. Establish the displacement and the RPO code before ordering.