P0304 on a Chevrolet Silverado 1500

What P0304 usually means on a Silverado 1500

P0304 pins the misfire to cylinder 4, which on the AFM 5.3L Silverado is one of the four deactivating cylinders. That makes a collapsed AFM lifter a leading suspect when cylinder 4 misfires hard and the engine ticks, as opposed to a simple coil or plug issue. On non-AFM engines the usual single-cylinder suspects apply. As with the other AFM cylinders, the branch point is whether a lifter tick accompanies the misfire.

Most likely causes on this model

1. Collapsed AFM lifter on cylinder 4 (5.3L)

   Cylinder 4 is an AFM cylinder, so a hard misfire there with a tick strongly suggests a failed AFM lifter, an internal mechanical fault.

2. Failed coil or worn spark plug on cylinder 4

   The everyday single-cylinder cause. Swap the coil to test, and inspect the plug for wear or fouling.

3. Oil-fouled plug from AFM oil consumption

   Burnt oil on an AFM 5.3L can foul cylinder 4's plug, causing a misfire that returns unless consumption is addressed.

4. Injector or compression problem on cylinder 4

   A leaking injector or low compression, including a lobe damaged by a failed lifter, causes a misfire ignition parts cannot fix; confirm with a compression test.

What it costs on a Silverado 1500

A coil and plug for cylinder 4 is cheap; a collapsed AFM lifter is not, requiring intake and valvetrain teardown at a four-figure cost and an inspection of the cam lobe for that cylinder. Confirming whether this is a lifter or an ignition fault before disassembly is essential to avoid unnecessary work.

Fixing it

Check for a tick and test compression on cylinder 4 first. If ignition parts are good and the cylinder is an AFM cylinder ticking under load, plan for lifter replacement and inspect the camshaft.

For the full step-by-step diagnosis order (any vehicle), see the main P0304 guide.

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