Precision Raceworks M3/M4/M340i/M440i (G8x/G2x) Stand Alone AFS™ – BMW B58/S58

Overview

Once you add port injection to a direct-injected M340i/M440i (B58) or M3/M4 (S58), the factory low-pressure fuel system becomes the weak link. The factory pump is controlled by PWM designed to reduce output once target fuel pressure (typically 5 bar) is reached — which puts it in constant conflict with any upgraded or added pump trying to feed port injection. On top of that, the high-pressure pump's control system dumps fuel back into the low-pressure system at high pressure/low volume, causing pressure oscillations that limit how consistently an upgraded pump can perform.

The Precision Raceworks Stand Alone AFS™ (Auxiliary Fuel System) solves this at the source: instead of trying to make the factory low-pressure system do double duty, it adds a completely dedicated, independent fuel system just for your port injection setup. Now featuring plug and play connectors and AN8 adapters, so it's no longer necessary to cut the factory harness.

SPECS

• Dedicated system: A fully separate low-pressure fuel system for port injection — completely independent of the factory pump and its PWM control
• Billet top hat: Billet aluminum top hat with 3 high-flow fuel ports
• Fully adjustable regulator: 1:1 boost-scalable billet fuel pressure regulator
• Filtration: 10-micron USA-made Microglass fuel filter, ideal for E85
• Lines: Smooth-bore, high-flow PTFE feed and return lines (AN6)
• Pump Selection: AFS.425 — single Walbro 450, 425 LPH @ 3 bar; AFS.460 — single Walbro 535, 460 LPH @ 3 bar; AFS.640 — dual Walbro 450s, 640 LPH combined @ 3 bar; AFS.745 — Walbro 450 + Walbro 535, 745 LPH combined @ 3 bar; AFS.800 — dual Walbro 535s, 800 LPH combined @ 3 bar
• 100% ethanol compatible: All components rated for full E85 compatibility

PARTS INCLUDED

• Walbro fuel pump(s) per selected configuration
• Billet aluminum top hat and fuel pressure regulator
• 10-micron Microglass fuel filter
• PTFE feed/return lines and fittings
• Configurable pump activation harness

TECH RESOURCES

• Designed for use with a port injection kit where the fuel rail is mounted above the manifold. If you're running a plate-style spacer PI setup, confirm compatibility before ordering.
• Some fuel rails may require a Male AN8-ORB to Female AN6-ORB adapter for compatibility (not included).
• If your tuner wants Solid State Relays, one kit is needed per pump.
• PDF Instructions - Click Here
• Video Instructions - Click Here
• Pump Activation Harness - Click Here
• Setting Fuel Pressure - Adjustable Regulator

Part Numbers: 601-0281 (AFS.425) / 601-0282 (AFS.460) / 601-0283 (AFS.640) / 601-0284 (AFS.745) / 601-0285 (AFS.800)

Vehicle Application