* Ignition Coil Issues (despite replacement): Even if you replaced the coil, there could still be an issue. A coil might be failing under high load (heat) or have a cracked internal component. Consider:
* Cracked coil: A seemingly good coil might have a hairline fracture that only shows up under stress.
* Worn coil: The coil might be weak even if it *appears* to work at lower RPMs.
* Coil pack connection: Inspect the connection to the coil pack itself and ensure it is secure and there's no corrosion.
* Worn or Damaged Injectors: At higher speeds, fuel delivery demands increase. A clogged or malfunctioning injector on cylinder 2 might struggle to keep up under pressure, causing a misfire at higher speeds. This is a common culprit.
* Wiring Issues (beyond the plugs): While you replaced the spark plug wires, inspect the wiring harness carefully for any damage, especially near the distributor (if your car uses one) or the coil pack. Look for cracks, fraying, or chafing against other parts of the engine.
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is positioned. A failing CKP sensor can cause misfires, especially at higher speeds because the timing becomes more critical.
* Mass Airflow Sensor (MAF): An inaccurate MAF sensor can send the wrong fuel/air mixture signal to the ECU, leading to misfires. A problem would be more noticeable at higher speeds where the air intake is higher.
* Fuel Pump: A weaker fuel pump may struggle to supply sufficient fuel under high-demand situations, such as at 70+ mph. This is less likely if the issue is isolated to just one cylinder, though.
* Vacuum Leak: A leak in the intake system could affect the air/fuel mixture, again more noticeable at higher speeds.
Troubleshooting Steps:
1. Re-check Cylinder 2 Coil: Even if new, carefully inspect the coil for cylinder 2 again.
2. Check Injector for Cylinder 2: This requires either a fuel pressure test or (more complex) an injector flow test.
3. Inspect Wiring Harness: Look closely for any signs of damage to the wiring harness, particularly around cylinder 2.
4. Professional Diagnosis: The most effective solution might be to take your car to a qualified mechanic. They can perform a diagnostic scan to identify the specific fault code(s) related to the misfire. This is highly recommended given your troubleshooting efforts so far.
Important Note: Continuing to drive with a misfire can cause damage to your catalytic converter. It's best to limit high-speed driving until the problem is resolved.
