Ram 1500 P0303 Misfire Diagnosis: Spark, Compression, and Injector Issues
My 2015 Ram 1500 started exhibiting a rough idle, followed by the engine light coming on. After reading the OBD2 code, I found it was P0303 — indicating a misfire in cylinder #3. I replaced the spark plug and ignition coil with known-good components, but the issue persisted. Compression testing showed normal readings. To isolate the problem, I swapped the #3 cylinder's wiring harness to a spare ignition coil and grounded the spark plug. The engine produced a visible spark, confirming good ignition component function. Using my mechanic’s stethoscope, I heard the #3 fuel injector clicking during operation — similar in rhythm to other cylinders — suggesting it is receiving signals. After clearing the codes and reconnecting all components, the engine triggered P0357 — indicating a misfire related to cylinder #3's ignition coil or control circuit. However, prior to this, only P0303 was present. I’ve replaced the fuel injector for cylinder #3 with no improvement. I’m now considering using a noid light to verify if the coil is actually receiving proper signal control. Additionally, I discovered there’s no dedicated attachment point on the fuel rail for a fuel pressure gauge — requiring disconnection of the fuel line and installation of an adapter. This design seems intentionally difficult for DIYers. I’m wondering: could this be a wiring issue between the ECU and coil? Or is it possible that the injector has internal failure despite normal clicking sound? Any insights or troubleshooting steps would be greatly appreciated.
Clear all codes and observe if P0357 returns. Did you have P0357 before? If not, it may indicate a new fault after the coil swap. Confirm spark from cylinder #3 using a test light — connect to battery positive and ground; the tan/orange wire should flicker with engine operation, while the dark green/orange wire stays lit. If good spark and plug are clean, and compression is normal, consider injector issues. Clicking sound doesn’t confirm fuel flow or pressure — use a scan tool and fuel pressure gauge for proper injector performance testing. Try swapping injectors to another cylinder and clear codes; if P0357 follows the injector, it points directly to that component.