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Random / Multiple Cylinder Misfire
🔴 CRITICAL — STOP DRIVING POWERTRAIN · Ignition System
PCM detected misfires on multiple cylinders—no single cylinder is consistently misfiring.
What You'll Notice
- Severe rough idle — cabin vibration noticeable
- Flashing MIL (catalytic converter protection mode)
- Power loss across RPM range
- Rotten-egg smell from exhaust (unburned fuel hitting cat)
- Possible stall at idle
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)
Direct Repair Steps
- Start with: pull all spark plugs, inspect tip — replace full set to OEM spec gap
- Swap ignition coil(s) sequentially to identify a faulty coil; replace confirmed bad coils
- Compression-test all cylinders; readings below 150 psi (or >10% variance) indicate internal engine wear
- Check fuel pressure AND volume (flow test); replace pump if pressure drops under load
- If oil-related: change oil + filter, run with proper viscosity, recheck for lifter tick
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Check PriceQuick answers
What does P0300 mean?
PCM detected misfires on multiple cylinders—no single cylinder is consistently misfiring.
Is P0300 serious?
It depends on the system and symptoms, but the page ranks the severity and likely causes so you can decide whether to stop driving or continue with caution.
What should I buy before troubleshooting P0300?
A reliable OBD2 scanner helps confirm the code, read live data, and avoid guessing before repairs.