Why an engine needs extra fuel after it starts
Right after a start, especially a cold one, the intake ports and the backs of the intake valves are cool and dry. Some of the fuel you inject sticks to those surfaces as a film instead of making it into the cylinder. Until that film builds up and things warm up, the engine gets less fuel than the injectors are delivering, so it runs lean and can stumble or stall.
The Post Start Correction table in NSP adds fuel for a short time after start-up to make up for that loss. It works alongside the coolant temp correction, which handles the longer warm-up, and the fuel prime pulse, which wets things before cranking.
How to tune it
- The table is set against how long the engine has been running, and is usually also mapped against temperature. Cold starts need more correction, for longer.
- Log lambda for the first minute after each start. If it goes lean and then recovers, add correction in that time window. If it runs rich and lazy, take some out.
- Test over several cold starts on different days. One good start doesn't prove much.
Make sure the final Engine Running Time column is zero, at least at normal operating temperature. Whatever is in that last column keeps being added to fuel delivery no matter how long the engine has been running. A small leftover value there will quietly skew every fuel table you tune afterward.
Ignition has a matching table too. See ignition post start correction, and fuel corrections for how all the fuel corrections stack together.
