What Flow Percentage does
With injection staging, the Nexus splits the engine's total fuel demand between two or more sets of injectors. Normally the secondaries only start working once the primaries hit their Staging Duty Cycle. The Flow Percentage table changes that. It lets you ask a stage to carry a set share of the total fuel, whether or not the stage below it is full.
A few ground rules:
- It only exists for Stage 2 and higher, and only with Nexus Style staging.
- Stage 1 never gets a Flow Percentage table. It always delivers whatever fuel is left over.
- Each stage still stops at its own Staging Duty Cycle. Any fuel it cannot deliver is handed to the lower stages.
How it plays out
Picture a two-stage engine with both stages capped at a moderate staging duty. Here is what happens as you raise the Stage 2 Flow Percentage:
| Stage 2 Flow % | Stage 1 status | Who delivers the fuel |
|---|---|---|
| 0% | Below its cap | Stage 1 does everything. Stage 2 is idle |
| 0% | At its cap | Stage 2 picks up only the extra fuel Stage 1 cannot supply, even though the table still reads 0% |
| Around 30% | Any | Stage 2 carries about 30% of total demand, and Stage 1 duty drops to match |
| Higher | Any | Stage 2 carries more, and Stage 1 duty falls further |
In short, the table moves fuel from Stage 1 to Stage 2 on purpose, instead of waiting for Stage 1 to fill up.
Why you would use it
Common reasons are spreading fuel between port and upstream injectors for better mixing or charge cooling, keeping secondaries firing a little so they never sit dry, or making the handover between stages less abrupt. Map it against something like RPM or manifold pressure so the split changes with load.
Never put a channel on either axis that depends on another stage's duty cycle. The output of the table changes those duties, which changes the axis, which changes the output. That feedback loop is how you get fuel oscillating between stages.
Setting it up without surprises
- Get the injector data right first: Flow, Dead Time and the Short Pulse Width Adder for every stage. Flow Percentage assumes the ECU knows exactly what each injector delivers.
- Start with the table at 0% and confirm normal staging works.
- Bring in small percentages in one area at a time, and watch lambda and each stage's duty in the log.
- If lambda shifts when the split changes, the injector data is off, not the table.
Related: Base - Stage 2 and Firing Angle BTDC.
