How long term trim works
Normal knock control retards timing the moment it hears knock, then recovers. Long term trim adds memory. It keeps a table the same shape as your ignition map, and every time knock is detected in a cell, it stores some retard in that cell. Next time the engine runs there, the learned retard is already applied.
Tick Enable Long Term Trim to turn it on. It's only as good as your knock detection, so set up the knock threshold properly first.
| Setting | What it does | Our advice |
|---|---|---|
| Long Term Retard | Retard added to a cell for each knock event detected there | Small steps. Let repeated events build it up |
| Max Long Term Retard | The most retard the table can learn | Enough to protect the engine, not so much it hides a real problem |
| Reset | Clears the learned table to 0 | Use after changing the ignition map or fuel |
| Apply to base Table | Writes the learned values into the ignition base table | Review the numbers before you apply them |
Restore: giving timing back
Tick Enable Long Term Ignition Restore and the ECU will slowly take back learned retard in cells where it samples and hears nothing.
- Long Term Restore Amount: how much advance is added back each time a cell passes without knock. It keeps adding until it reaches the Max Restore limit.
- Restore Sample Rate: how often those restore steps happen.
- Max Restore: the limit on restoring. Positive values are advance, so a positive number here means the table can learn timing beyond your base ignition map.
Letting the ECU learn advance past your map is only safe if your knock detection is genuinely reliable. On a new setup we keep it at 0 so restore can only undo learned retard, not add new timing.
How we use it
We treat the learned table as information. After some driving, look at which cells collected retard. Clusters usually point to a fuel, heat or map problem worth fixing properly. When you're happy the learned values are genuine, use Apply to base Table to fold them in, then Reset so the trim starts fresh. For multi-bank engines, bank long term trim works the same way per bank. Knock sensor wiring is covered in knock wiring, and if you need a sensor, we stock the Bosch knock sensor.
