P0300

Chevy Random / Multiple Cylinder Misfire

Specialized diagnostic report for Chevy owners dealing with the P0300 fault code.

Technician's Overview

🔴 CRITICAL — STOP DRIVING

PCM detected misfires on multiple cylinders—no single cylinder is consistently misfiring. When this code is triggered in a Chevy, the engine control module (ECM) has detected an issue with the Ignition System system.

Common Symptoms
  • Severe rough idle — cabin vibration noticeable in my Chevy
  • Flashing MIL (catalytic converter protection mode) in my Chevy
  • Power loss across RPM range in my Chevy
  • Rotten-egg smell from exhaust (unburned fuel hitting cat) in my Chevy
  • Possible stall at idle in my Chevy
Probable Causes
  • Distributor cap or high-tension leads cracked/arcing
  • Worn or incorrectly gapped spark plugs across all cylinders
  • Low compression across multiple cylinders — worn rings or burnt valves
  • Injector rail pressure drop — failing fuel pump or pressure regulator
  • Bad ignition coil pack or failing crankshaft position sensor
  • Contaminated engine oil causing hydraulic lifter collapse (GM V8)
Recommended Fixes for Chevy
  1. Start with: pull all spark plugs, inspect tip — replace full set to OEM spec gap
  2. Swap ignition coil(s) sequentially to identify a faulty coil; replace confirmed bad coils
  3. Compression-test all cylinders; readings below 150 psi (or >10% variance) indicate internal engine wear
  4. Check fuel pressure AND volume (flow test); replace pump if pressure drops under load
  5. If oil-related: change oil + filter, run with proper viscosity, recheck for lifter tick
QUICK FIX TOOL

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