What lives on this page
Your main spark map gets most of the attention, but a lot of the ignition behavior that makes a car start well, idle cleanly and protect itself sits in the settings around it. On a Nexus ECU, NSP groups them into three areas: how the ignition angle is calculated, conditional base tables that take over in specific situations, and extra functions like rate limiting and knock control.
Ignition angle settings
| Setting | What it does | Our advice |
|---|---|---|
| Lock Mode | Freezes timing at one fixed value. Every table and correction is ignored while it's active | Use it to set TDC offset, then put it back. The default is On During Clear Flood Only |
| Firing Angle | The fixed timing used while locked, in degrees BTDC | Pick a value that's easy to read on your timing marks |
| Trailing Split Angle | Rotary only. The retard between leading and trailing plugs | Match your engine's timing mark arrangement |
| Ignition Load Type | The sensor treated as ignition load, used whenever a table's axis is Ignition-Load | MAP by default, which suits most engines |
Why lock mode matters
Before you tune timing, the ECU's idea of where the crank is has to agree with reality. Lock the timing, check it with a timing light, and adjust the TDC offset until the light matches the firing angle. If your offset is wrong, every number in your spark table is wrong by the same amount, and the ECU has no way of knowing. Our timing light guide walks through it.
Take lock mode off when you're done. A car left locked at a fixed angle ignores every table, including anything protecting the engine from knock.
Rotary split, by example
Many rotary engines have factory marks at 5 and 20 degrees after TDC. To check those, you'd lock the leading timing at a firing angle of -5 and set a trailing split angle of 15, which is 15 degrees of extra retard, putting the trailing plugs at -20.
Conditional base tables
These replace the main map when the engine is in a particular state:
- Cranking Ignition Angle: used while RPM is below the Max Cranking RPM setting. Enabled by default, and it can be up to 3D. Cranking timing that's too advanced fights the starter. Too retarded and the engine is slow to fire.
- Zero Demand Ignition Angle: only active when throttle position (cable) or pedal position (DBW) is below the Zero Fuel Demand value. It can be up to 2D. This is where we shape idle and overrun timing without disturbing the main table.
Functions
Attack and decay rate
These two tables limit how fast timing is allowed to change, in degrees per engine cycle:
- Attack limits how quickly timing moves toward more advance. It's the one people actually use, mainly to soften the torque jump when timing would otherwise snap forward, such as coming out of a retard correction.
- Decay limits how quickly timing moves toward retard. It's rarely needed, so its defaults are high, around 50, so it doesn't get in the way.
Both can be up to 3D and are disabled by default. Our starting point is to leave them off until a log shows a harsh step you want smoothed.
Knock control
When knock sensors detect detonation, knock control pulls timing. Short term retard reacts to knock as it happens. Long term trim learns where knock keeps recurring and holds retard there, covering you if the tune is too aggressive in some area. It's a safety net, not a substitute for a safe map. Set it up with the knock control guide.
Common questions
My timing light doesn't match NSP. What's wrong?
Usually TDC offset. Lock timing, confirm with the light, and adjust the offset until they agree. Then unlock.
Should I change the ignition load type?
Only with a reason, such as an engine with a very unsteady MAP signal. For most setups the default MAP input is correct. The main table itself is covered in base ignition angle.
