Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code P0300, Random Misfire Detected - "S" & "T" Series 4.3L (VIN W): Notes
Misfire is detected using cam and crankshaft sensors. Control module monitors both sensors. When control module senses crankshaft deceleration not associated with normal engine speed reduction, camshaft position is used to determine misfiring cylinder. Control module determines misfires on each cylinder and can thus evaluate a random misfire and set code.
- If other codes are set, they may be responsible for misfires.
- It may be necessary to test drive vehicle to duplicate misfire conditions.
- When checking spark, spark should be consistent. A few sparks and then nothing constitute a no spark.
- At this point, ignition is okay. Problem may be fuel related.
- Determines if fuel injector is functioning properly.
- Determines if poppet nozzles are functioning properly.
- Both fuel and ignition are okay, problem is mechanical in nature.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.