2002 Chevrolet S10 2.2L 4-Cylinder P0303 Misfire: Diagnosis & Repair Steps
My 2002 Chevrolet S10 2.2L 4-cylinder pickup is experiencing a misfire with the check engine light illuminated. The OBD2 scanner shows trouble code P0303, indicating a misfire in cylinder 3. I recently replaced the ignition coil for cylinder 3 and all spark plug wires and plugs. After clearing the code, I started the truck and ran it at 2 RPM while giving it gas. Within about 7 minutes, the engine light returned with the same P0303 code. The scanner now displays three instances of P0303: 'P0303 Mod $10', 'P0303 Engine', and 'P0303 Engine'. I’ve tried testing the spark plug wire and found that it fires properly when connected to a multimeter — the meter shows movement, indicating the wire is functional. Accessing the fuel rail for cylinder 3 is difficult as it's located beneath the manifold pipes under the engine head. I can only reach two of the four injectors easily. I’ve already removed the plug wire from cylinder 3 and tested its firing — it works. I’m considering replacing the number 3 fuel injector, but I don’t know how to safely remove the fuel rail without damaging components. Are there step-by-step online guides or photos showing how to access and replace injectors on a 2002 Chevrolet S10? All four fuel injectors were replaced about five years ago by the dealership due to a check engine light, but they did not specify which code triggered the replacement. Since then, the issue has returned and persists. Any advice or diagnostic tips would be greatly appreciated — especially if you suspect a dirty injector, compression issues, or vacuum leaks near cylinder 3.
Does the misfire occur only at idle or under load? A clogged fuel injector could be the culprit. Try using a fuel system cleaner like Techron Total Fuel System Cleaner, available at AutoZone. The most reliable way to test injectors is with an injector balance test. Cleaning may resolve the issue in some cases. Compression problems should also be ruled out. Additionally, check for vacuum leaks near cylinder 3 — use propane and run it along gaskets; listen for a change in RPM or smoother engine operation. Injector balance tests require specialized tools such as a timing device or a scan tool with bi-directional control functions. A quality OBD2 scanner can monitor misfire counts and fuel trim values. Without proper diagnostic equipment, accurate diagnosis is challenging. What did the spark plug look like when removed? Was it dirty or worn?