* Oxygen Sensor(s): The high-flow cat and u-bend delete significantly alter exhaust flow. This can confuse the oxygen sensors, leading to inaccurate readings and a CEL. The PCM (Powertrain Control Module) is trying to compensate for what it perceives as a lean or rich condition.
* Mass Airflow Sensor (MAF) reading discrepancies: Your cold air intake changes the air density and airflow compared to the stock setup. The MAF sensor might be reading values outside the PCM's programmed parameters, triggering a code related to air/fuel ratio.
* Pulley Size: A smaller pulley increases boost pressure. If the boost pressure is excessive, it can cause various issues, including triggering a CEL for overboost or other related problems. This is especially likely if your engine management system hasn't been tuned to accommodate the increased boost.
* Incorrect Installation: A poorly installed part (e.g., a loose connection, vacuum leak) could be causing the problem. Double-check all connections and ensure everything is properly secured.
* Pending Codes: Sometimes, a temporary condition can cause a pending code, which might eventually trigger the CEL if the condition persists.
* Other Sensors: Other sensors, like the throttle position sensor or knock sensors, could be affected either directly or indirectly by the modifications. Extreme boost levels from the smaller pulley could put additional strain on engine components, potentially triggering these sensors.
How to diagnose:
1. Get the codes read: The most crucial step. A code reader (OBD-II scanner) will give you specific trouble codes (P-codes). These codes will pinpoint the problem area. Auto parts stores often offer free code reading services.
2. Check for vacuum leaks: Carefully inspect all vacuum lines and connections, especially those affected by the modifications.
3. Inspect for loose connections: Make sure all sensors and components are securely connected.
4. Consider a professional tune: With significant modifications like yours, a professional tune is highly recommended. A tune adjusts the PCM's parameters to work correctly with the upgraded components, preventing issues like overboost and inaccurate sensor readings. This is likely the most effective long-term solution.
Without knowing the specific trouble codes, pinpointing the exact cause is difficult. Get the codes read, and that will guide the troubleshooting process. Don't ignore the CEL; driving with a problem could cause further damage to your engine.
