What this page controls
Before the ECU can deliver the fuel your VE or fuel table asks for, it needs to know the hardware: how many injector outputs you're using, whether they're one group or several stages, and when in the engine cycle they should fire. That's all set on the Fuel System page in NSP.
Injection system settings
| Setting | What it does | Our advice |
|---|---|---|
| Disable Injectors | Shuts off every injector output (default Disabled) | Handy for cranking to check trigger and ignition without fueling. Remember to turn it back off. |
| Enable Short Pulse Width Adder | Adds a Short Pulse Width Adder table to each stage, to lengthen very short pulses where the injector doesn't flow in a straight line | Turn on when you have good injector data or you're chasing idle and light cruise fueling on big injectors. |
| Injector Timing Method | Times each pulse by where it starts or where it ends relative to TDC (default End of Injection) | Leave on End of Injection unless you have a specific reason. |
| Number of Stages | How many separate groups of injectors you run | One for most cars. Two or more for secondary injectors or very high flow builds. |
| Cylinder and Bank Correction Stages | Chooses which stages the per-cylinder and per-bank trims are applied to | Only include stages with one injector per cylinder. A throttle body or plenum-mounted stage feeds every cylinder, so trims on it can't target one. |
| Stage Flow Percentage Tables | Adds a flow percentage (flow proportion) table in each stage's Fuel Tuning node | Use it when you want to choose exactly how the fuel is split between stages. |
Staging method (Elite ECUs)
When an Elite ECU runs more than one stage in NSP, you choose how the stages share the load.
Nexus Style
This is the one to use on a fresh Elite install that hasn't been fuel-tuned yet. Stage 1 does all the work until it hits its Stage 1 Staging Duty Cycle. It then stays at that duty while stage 2 ramps in, and the same hand-off repeats for any further stages. If every stage is sitting at its staging duty and the engine still wants more, they all climb together, at whatever individual rates get them to 100% at the same moment.
With Stage Flow Percentage Tables on, those tables decide what share of the total each stage delivers, up to its staging duty. Any stage that reaches its staging duty passes the excess to the others, and once they're all capped they rise together to 100% as above. Leaving every flow table at 0% makes it behave exactly as if the tables were turned off.
Elite Style (Legacy)
Here every active stage runs the same duty cycle. Stages are added when the highest active one goes over the Max Duty Cycle setting and dropped when it falls under Min Duty Cycle. Keep it only for a tune that was already built this way. If you're going to retune the fuel anyway, switch to Nexus Style.
Staging set up, per stage
- # Of Injector Outputs: how many physical injector outputs this stage uses.
- Injection Mode: how the stage delivers fuel. Sequential is the default.
Injection modes compared
| Mode | How it fires | Trigger needed | When we use it |
|---|---|---|---|
| Sequential | Each output fires once per engine cycle, timed to its own cylinder, delivering the full amount | Full-cycle sync, normally crank plus cam sensor | Always, when the hardware allows |
| Semi-Sequential | Each output fires every crank turn (twice per cycle) for a pair of cylinders, delivering half each time | Half sync at minimum, such as a missing tooth crank wheel with no cam sensor | No cam sensor, or not enough injector outputs |
| Batch | Outputs split into two groups that take turns | One trigger per spark event | Older or simple trigger setups |
| Multi-Point | All outputs fire together | One trigger per spark event | Simple setups and some throttle body stages |
Choosing Batch or Multi-Point unlocks an Injections Per Cycle setting.
Semi-sequential pairs
In semi-sequential, each output drives two cylinders whose pistons move together, so their intake events are one crank revolution apart. Common pairings by firing order:
| Firing order | Output 1 | Output 2 | Output 3 | Output 4 |
|---|---|---|---|---|
| Inline four, 1-3-4-2 or 1-2-4-3 | 1+4 | 2+3 | - | - |
| Four cylinder, 1-3-2-4 or 1-4-2-3 | 1+2 | 3+4 | - | - |
| Four cylinder, 1-4-3-2 | 1+3 | 2+4 | - | - |
| Six cylinder, 1-5-3-6-2-4 | 1+6 | 2+5 | 3+4 | - |
| Six cylinder, 1-2-3-4-5-6 | 1+4 | 2+5 | 3+6 | - |
| Six cylinder, 1-6-5-4-3-2 | 1+4 | 3+6 | 2+5 | - |
| V8, 1-8-4-3-6-5-7-2 or 1-8-7-2-6-5-4-3 | 1+6 | 5+8 | 4+7 | 2+3 |
| V8, 1-3-7-2-6-5-4-8 | 1+6 | 3+5 | 4+7 | 2+8 |
Double-check your harness against the Fuel System > Wiring node before first start.
Troubleshooting
| Symptom | Usually |
|---|---|
| Sequential mode won't sync or run | Trigger setup can't see a full engine cycle. Check the cam input. |
| No injector pulses at all | Disable Injectors left on, or outputs not assigned. See injector diagnostics. |
| Cylinder trims do nothing | Correction stages set to a stage that doesn't have one injector per cylinder |
| Lumpy fueling at idle on big injectors | Short pulse behavior. Consider the Short Pulse Width Adder. |
Once the hardware side is set, confirm fuel density and your engine configuration before you start tuning.
Fuel system FAQ
Is sequential injection worth it?
Yes. It gives the most consistent fueling and the best idle and emissions, and it's the default for a reason. Semi-sequential is a fallback, not an upgrade.
Should I switch an existing Elite tune to Nexus Style staging?
Only if you're prepared to retune the staged area of the fuel map. The fuel split changes, so the old numbers won't carry across unchanged.
