Quick answer: A GMC Sierra misfire commonly stores P0300 or a cylinder-specific code, and on 5.3L and 6.2L V8 engines with Active Fuel Management the leading serious cause is a collapsed lifter on a deactivating cylinder. Before assuming that, rule out worn spark plugs and failed ignition coils – they cause the majority of misfires and cost a fraction as much.
The Sierra shares its powertrain with the Silverado, and both are heavily searched for misfire codes. This guide separates the routine ignition causes from the AFM lifter problem that defines this engine family.
Why the Sierra Misfires
GM’s Active Fuel Management (later Dynamic Fuel Management) shuts down cylinders under light load to save fuel. The lifters on those cylinders are a documented weak point: when one collapses, that cylinder stops firing properly and the misfire will not move no matter how many coils you swap. Alongside that, ordinary coil and spark plug wear accounts for most Sierra misfires on trucks with normal maintenance gaps.
For the full misfire explanation, see our main guide: P0300 – Random/Multiple Cylinder Misfire Explained.
Most Affected Sierra Years
- 2007-2013 (5.3L with AFM): Lifter failure and related oil consumption are widely reported.
- 2014-2019 (5.3L / 6.2L): AFM lifter concerns continue; coil wear is common.
- Any Sierra past 100,000 miles: Plugs and coils are usually overdue.
Symptoms on the Sierra
- Flashing check engine light during an active misfire.
- Rough idle and vibration at a stop.
- A distinct tick from the top of the engine – the key lifter clue.
- Oil consumption between changes on AFM-equipped trucks.
Common Causes (Cheapest First)
- Worn spark plugs – replace the full set together.
- Failed ignition coil – swap between cylinders to confirm.
- Fuel injector fault – less common but worth testing.
- Collapsed AFM lifter or camshaft lobe wear – indicated by a tick plus a fixed-cylinder misfire.
Check These Yourself First
- Check whether the misfire stays on one cylinder – that points internal.
- Listen for a tick at idle with the hood open.
- Check oil level; AFM lifter problems often accompany oil consumption.
Estimated Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Spark plugs (set of 8) | $40 – $120 | $150 – $320 |
| Ignition coil (one) | $40 – $110 | $60 – $130 |
| AFM lifter and camshaft repair | $700 – $1,800 | $1,500 – $3,200 |
Note: 2026 US estimates. Confirming ignition versus lifter before ordering parts is the biggest saving available on this engine.
Frequently Asked Questions
How do I tell an AFM lifter failure from a bad coil?
Swap the coil with an adjacent cylinder. If the misfire follows the coil, it is ignition. If it stays on the same cylinder – especially with a ticking noise – a collapsed lifter is likely.
Does AFM cause oil consumption too?
AFM-equipped engines have a documented association with higher oil consumption, and low oil accelerates lifter wear. The two problems often appear together on high-mileage trucks.
Can I keep driving with a misfire?
Not with a flashing light. An active misfire sends raw fuel into the exhaust and can destroy the catalytic converter, turning a moderate repair into a much larger one.
Related: P0300 full guide · P0301 cylinder 1 · P0420 catalyst