2003 Mitsubishi Eclipse P0303 Misfire on Cylinder 3 - Diagnosis and Repair Guide
My 2003 Mitsubishi Eclipse 4-cylinder is showing a misfire on cylinder 3, as confirmed by an OBD-II scanner. The auto parts store initially suggested the issue was caused by bad gas, recommending I drain out old fuel and refill with high-octane gasoline. I tried both 83 octane and 93 octane, but the misfiring persists—my car still sounds like it's skipping or stalling. After further research, I found that P0303 (misfire on cylinder 3) can have multiple causes, including fuel contamination, faulty spark plugs, or failing coil packs. Given that my vehicle is a 2003 Eclipse with an 83-octane requirement in some regions, I'm concerned about whether the gas type was actually appropriate. The misfire doesn't seem to be isolated to one cylinder, and I believe this points toward a more mechanical or electrical issue rather than just poor fuel quality.
Please specify your vehicle's make, model, year, engine type, and location. Not all vehicles require 83 octane—most modern engines need at least 87. Where in the U.S. or internationally can you access 83-octane fuel? Also, auto parts stores primarily sell parts, not fuel diagnostics. Misfires have many potential causes—diagnosing them properly requires a systematic approach. Would contaminated gas only affect one cylinder? Probably not.