Port injection: wiring and controllers
Past ~500 whp the direct-injection system needs help. Port injection adds a second fuel circuit — here's how the controllers wire in and what protects the engine.
Direct injection gave the N54 its clean combustion and its ceiling. The high-pressure pump can only move so much fuel, and ethanol makes everything worse by demanding more volume for the same energy. Port injection — a second fuel circuit spraying into the intake runners at low pressure — is how the platform gets past it. The mechanical install is a plate, a rail, six injectors, and fuel lines; this guide is the electrical side and the controller logic that keeps it safe.
What PI is, mechanically
A port-injection kit adds a rail fed from the low-pressure side (~5 bar / 72 psi) — upstream of the HPFP entirely — with one spray injector per cylinder in a plate between the manifold and the head. The DI system stays and keeps carrying its share; PI supplements it progressively. Because it rides LP pressure, PI sidesteps the HPFP ceiling completely.
Sizing (on full E85, with adequate LPFP): 550 cc injectors support roughly 650 whp, 750 cc around 750 whp, 950 cc past 800. One gotcha everyone hits: injector flow is quoted at the industry test pressure of 43.5 psi, but the rail here runs ~72 psi — a "750 cc" injector flows about 1000–1050 cc in this service. Compare kits at real pressure or don't compare them.
The controller is the wiring job
The injectors are passive — the controller decides when and how much. Four credible options, matched to how the car is otherwise run:
| Controller | Best for | Control model |
|---|---|---|
| BMS JB4 PI controller | Cars already running a JB4 | Fully integrated — reads LPFP pressure, boost, gear, trims, AFR, injector current |
| Split Second AIC6 | Flash-only cars | Standalone duty table vs. boost pressure and RPM |
| Motiv ReFlex+ / Lite | Flash-only + flex fuel | CAN + analog I/O; AUX outputs can also trigger a second LPFP |
| Fuel-It/BMS CANfuel | B58/G-platform, N54 with JB4 | Sequential 8-injector driver on CAN, Bluetooth config |
None of them tap DME injector pulses — that's a common misconception. Load comes from the JB4's CAN view of the engine (integrated path), or from MAP + RPM (standalone path), or from crank/cam + CAN (sequential path).
JB4 PI controller wiring (N54)
| Wire | Lands on |
|---|---|
| Black ×2 | Ground |
| Red | JB4 power, green connector |
| Yellow | BMS data/Bluetooth dongle spot #9 |
| White | JB4 DB25 harness #15 (the meth-blue position) |
| Purple | JB4 small gray subconnector #21 (read from the female side) |
| Orange (thicker) | +12 V output for a second fuel pump or meth pump — 2 A max, must drive a relay |
Setup side: the board needs the 24K22 slave-chip firmware (G5 boards from 11/2015 on), Fuel Bias = 50 across the table, meth scaling = 99, and Menu 8 = 0 rpm unless a 2-step relay is fitted — with the wrong menu-8 value PI is silently blocked from activating.
AIC6 wiring (standalone path)
| Wire | Lands on |
|---|---|
| Red | +12 V, engine bay |
| Black | Ground |
| Green | T-MAP sensor signal (boost) |
| Yellow/Black | OBD pin 9 (RPM) |
What makes a PI install safe
Fuel added by an aftermarket box is the highest-consequence wiring on the car. In order of importance:
- **MHD's PI Safety flash option** — cuts ignition to a cylinder whose port injector stops flowing. On any MHD-format file we consider it required, not optional.
- **The JB4 PI controller's failsafe set**: PI duty dynamically scaled from measured LP pressure (flow stays honest as the pump sags); instant cut on lift-off or traction events (no intake backfires); AFR monitoring with cut on misfire detection; per-injector current monitoring (clogged injector, blown fuse, loose ground); failsafe on bank-to-bank trim mismatch >15%; auto-scaling with flex ethanol content.
- **The physical layer**: EV6/US-car connectors fully seated, the controller grounded where the engine grounds, and the LP tap done with proper hose and clamps — a PI fuel leak at 72 psi is a fire, not a trim problem.
How PI and the rest of the fueling stack interact
PI moves the ceiling, it doesn't raise the floor: the low-pressure supply feeding the rail has to keep up (the LPFP guide covers pumps and second-pump wiring), the flex sensor tells the blend what's in the tank, and on a single-turbo car the DME may be watching one bank (the single-bank guide). Logs tie it together — LPFP pressure, PI duty, lambda, and ethanol in one pull tell you whether the stack is feeding the engine or flattering it.
Sources
- N54 port injection end-to-end: [bmwtuning.co PI guide](https://bmwtuning.co/ultimate-bmw-n54-port-injection-guide/)
- JB4 PI controller wiring + failsafes (vendor thread): [JB4tech N54 port injection](https://www.jb4tech.com/forum/model-specific-engine-tuning-modification-discussion/n54/3625-n54-port-injection)
- CANfuel controller: [burgertuning.com CANfuel](https://burgertuning.com/products/canfuel-sequential-port-fuel-injection-controller)
When does an N54 need port injection?
Around 500 wheel horsepower, sooner on ethanol. The stock fueling ceiling is roughly 450–500 whp on pump gas and 425–450 on E30; past that the low-pressure system gives first on ethanol blends, then the high-pressure pump. Port injection is the proven path past 500 whp on heavy E85 and supports 900+ whp on full E85 with the right pumps.
Do port injectors need their own power wiring?
No. PI injectors are passive solenoids on the controller's harness — EV6 connectors, fired by the controller's ground pulses. The only power wiring in a PI install is the controller itself and, if fitted, the relay it triggers for a second fuel pump or meth pump.