Encountering a check engine light (CEL) can be unsettling, especially when your car, usually running like a dream, starts acting up. That’s exactly what happened with my relative’s 2003 vehicle. Despite not being a frequent visitor to online forums lately, this was the first place I turned to when faced with this automotive puzzle. Initially, the driveability seemed normal, but at stop lights, a subtle rough idle crept in – a stark contrast to the usual silky smoothness of these cars when they’re in top condition. Then came the flashing CEL, a clear sign of a more serious issue demanding immediate attention.
Pulling out my scanner on Sunday revealed a series of misfire codes: P0300 (Random/Multiple Cylinder Misfire Detected), P0302 (Cylinder 2 Misfire Detected), P0308 (Cylinder 8 Misfire Detected), and P0316 (Misfire Detected on Startup – First 1000 Revolutions). Adding to the confusion, the readings from the B1S2 and B2S2 O2 sensors were out of range, specifically showing high fuel trim and voltage. This initially led me down the path of suspecting a faulty O2 sensor as the root cause, potentially triggering the misfires. Finding misfires in two cylinders simultaneously was unexpected, especially considering a recent major tune-up just 5,000 miles prior.
To start diagnosing car cylinder misfires, I began with the basics. I removed the ignition coils and spark plugs from cylinders 2 and 8. Visually, they appeared to be in good condition, and the coil resistance readings were within the specified range. After cleaning the spark plugs, ensuring the gap was correct, I reinstalled everything. Another scan showed improvement – the codes now only indicated P0308 and P0316. Cylinder 2 seemed to have resolved itself, at least temporarily. It was at this point that online forum wisdom pointed towards Coil-On-Plug (COP) issues as a common culprit for misfires in these models.
Suspecting a faulty COP, I decided to perform a coil swap. I exchanged the coil from cylinder 8 with the coil from cylinder 1, a cylinder that was currently running without issue. Running another scan confirmed my suspicion: the misfire had now moved to cylinder 1. This definitively indicated that the coil from cylinder 8 was indeed defective and the primary cause of the cylinder misfire.
While I was prepared to replace the coil myself, my relative, eager to get the car back in perfect running order, preferred a quicker solution and wanted to visit a local 24-hour mechanic. I took the car in, and the mechanic began his own diagnostic process. His approach involved spraying carburetor cleaner around the intake manifold, disconnecting coils one by one while the engine was running, and removing spark plugs. He started suggesting potential issues like a bad fuel injector. He even removed the suspected faulty coil from cylinder 1, tested it, and seemed ready to reinstall it. At this point, growing impatient with the seemingly misguided diagnosis, I intervened and suggested he simply replace the coil. He questioned my certainty, and I confidently stated, “Please just change that coil, it’s defective.” Fortunately, he listened, replaced the coil, and just like that, the problem was solved, costing only $49 for the part.
This experience, while slightly extended, reinforces the value of community knowledge and methodical DIY diagnostics. Even though the coil’s resistance was within specification, it was still faulty – a crucial detail learned from online forum discussions, particularly thanks to insights from experienced members like Dereck and V8_Dave. In the end, a focused approach based on shared expertise led to a quicker and more accurate diagnosis than a professional mechanic, highlighting that sometimes, the best car cylinder misfire diagnosis comes from informed car enthusiasts and a little DIY spirit.
