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2018 Silverado 1500 Rough Idle and Check Engine Light - P0304

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Heather Y. · rep 0 · May 22, 2:32 AM · 1 replies · solved · Question

Vehicle: 2018 Chevrolet Silverado 1500 LT

My 2018 Chevrolet Silverado 1500 LT, equipped with the 5.3L V8 engine, has been acting up lately. It started with a noticeable rough idle, especially when I'm stopped at a traffic light or in drive-thru lines. It's not constant, but it's definitely there.

Now, the check engine light has illuminated on the dashboard. I used my OBD-II scanner, and it pulled a P0304 code, indicating a misfire on cylinder 4. The truck also feels a bit sluggish under acceleration, and I've noticed a slight decrease in fuel economy.

I've got about 85,000 miles on the odometer. What could be causing this P0304 code and the rough idle? Any common issues for this model year and engine combination that I should investigate first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:32 AM

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The P0304 code specifically points to a misfire in cylinder 4. This is a common issue with several potential causes on the 5.3L V8 engine. Addressing it promptly is important to prevent further engine damage.

Common Causes for P0304:

  • Faulty Spark Plug: A worn or fouled spark plug in cylinder 4 is the most common culprit.
  • Defective Ignition Coil: The ignition coil for cylinder 4 might be failing, leading to an inconsistent spark.
  • Clogged or Failing Fuel Injector: If the fuel injector for cylinder 4 isn't delivering enough fuel, or is stuck open/closed, it will cause a misfire.
  • Vacuum Leak: A vacuum leak near cylinder 4 or in the intake manifold can lean out the air/fuel mixture, causing a misfire.
  • Low Compression: Less common, but a serious issue like a worn piston ring, valve problem, or head gasket leak can reduce compression in cylinder 4.
  • Active Fuel Management (AFM) Lifter Issues: On some GM V8s, AFM lifters can fail, leading to misfires and ticking noises. This is a more involved repair.

Troubleshooting Steps:

  1. Inspect Spark Plug and Coil: Start by visually inspecting the spark plug and ignition coil for cylinder 4. Look for cracks, carbon buildup, or signs of oil fouling on the plug. You can also swap the coil with an adjacent cylinder (e.g., cylinder 2) to see if the misfire code moves, indicating a bad coil.
  2. Check Fuel Injector: If swapping the coil doesn't resolve it, consider testing the fuel injector. You can use a noid light to check for pulse or listen with a mechanic's stethoscope for proper operation. A fuel pressure test might also be warranted.
  3. Look for Vacuum Leaks: Inspect all vacuum lines and the intake manifold gasket around cylinder 4 for any cracks or leaks. A smoke test can help pinpoint these.
  4. Perform a Compression Test: If the above steps don't yield results, a compression test on cylinder 4 (and adjacent cylinders for comparison) will determine if there's an internal engine issue.

When to See a Shop: If basic diagnostics like spark plug/coil inspection and swapping don't resolve the issue, or if you suspect a fuel injector problem, vacuum leak you can't find, or especially low compression, it's best to take your Silverado to a qualified mechanic. AFM lifter issues require specialized tools and expertise. Continued driving with a persistent misfire can damage the catalytic converter.

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