What it does
When enabled, the Pre Crank Prime Pulse fires a single pulse of fuel as soon as the ECU is powered on, before any cranking starts. The goal is to wet the intake runner walls. On a cold engine, the first fuel injected tends to cling to the ports as a film rather than reaching the cylinder. Laying that film down ahead of time means more of the fuel injected during cranking actually makes it to the cylinder, and the engine catches sooner.
Setting it up
Turn it on from the Fuel Tuning node in NSP. That enables the Pre Crank Prime Pulse table, where you set how much fuel is delivered. The biggest benefit is on cold starts, so aim for a prime that helps a cold engine catch without overfueling a warm one.
Our starting point: begin small, try several cold starts, and only add fuel if the engine is slow to catch. Too much prime just gives you a wet, smoky start or fouled plugs.
Built-in flood protection
Turning the key on and off a few times without starting would normally stack up prime pulses and flood the engine. The Nexus prevents that: it allows a maximum of three consecutive prime pulses between successful engine starts. After that, further key cycles don't add more fuel until the engine has run.
How it fits with other start-up fuel
Look at it alongside the fuel prime pulse and cranking fuel settings, because all of them add fuel around start-up. Tune them together. If you add a lot of pre-crank prime, you may need less cranking enrichment, and the other way around.
