What the TDC offset angle is
Your ECU sees the crank and cam trigger teeth, but it doesn't automatically know where those teeth sit relative to top dead center on cylinder 1. The TDC offset angle, often called the trigger angle, is the number of degrees between the trigger reference and TDC. Every spark and injection event is calculated from it. If it's off, all your timing is off by the same amount, even though the software shows the right numbers. That can mean a poor-running engine or, worse, hidden over-advance and detonation.
How we set it
- Get the engine running with a sensible base map and the trigger set up correctly for your engine.
- Use the ECU's timing lock feature to fix ignition at a known value.
- Check real timing at the crank with a timing light on cylinder 1.
- Adjust the TDC offset until the light reads the same as the locked value in the software.
- Save, then recheck at a higher idle to confirm it stays matched.
Make sure your timing marks are accurate before you trust them. A slipped damper ring or the wrong mark will throw off the whole process.
Going further
Sensor and signal delays can make timing drift slightly as RPM rises. The TDC offset angle table handles that fine adjustment. If you're running a distributor with two pickups, see verifying the TDC offset with a dual pickup distributor. For a real engine example, our 2JZ VVT-i trigger article covers the twin-cam 2JZ, and base map basics explains getting to first start.
