Quick Info
Model
450, 452
Estimated Cost
30-50€
Difficulty
Beginner
Time Required
10-15 min
Safety Notes
READ BEFORE STARTING: Working on the fuel pressure regulator involves handling pressurized gasoline.
Failure to follow these precautions can lead to fire, explosion, or serious personal injury.
Fire Prevention: * Work only in a well-ventilated area (ideally outdoors or in a garage with the door wide open).
Keep a Class B fire extinguisher within arm's reach at all times.Pressure Relief (Mandatory): * The fuel rail is under high pressure even when the engine is off.
Personal Protection (PPE): * Eye Protection: Wear wrap-around safety goggles. Fuel spray can cause permanent eye damage.
Skin Protection: Wear fuel-resistant gloves (Nitrile).Spill Management: * Even after pressure relief, a significant amount of fuel will remain in the rail and regulator housing.
Place several heavy-duty shop rags.Battery Safety: * Disconnect the Negative (-) battery terminal once the pressure is relieved. This prevents any accidental electrical sparks while you are handling open fuel lines.
Step-by-Step Guide
Introduction
The Smart Roadster’s fuel system is controlled by a mechanical regulator sitting at the end of the fuel rail. From the factory, most 0.7 units (including the Brabus) run a 3.8 bar regulator.
While this is fine for a stock car, enthusiasts often look to the Bosch 4.0 bar (Part No: 0280 160 575) as a "must-have" supporting modification.
Why the Bosch 0280 160 575?
Originally designed for Audi/VW performance engines, this Bosch unit is a direct "plug and play" fit for the Smart Roadster. It physically drops into the fuel rail housing without modification, allowing you to raise the fuel rail pressure by 0.2 bar.
The Benefits
Mid-Range Pull: Most owners report a "firmer" feel under acceleration, specifically in the mid-range (3,000 – 4,500 RPM).
Better Atomization: Higher pressure helps the injectors create a finer mist, which can lead to a cleaner combustion cycle.
Fuel Headroom: If your car is heavily modified (bigger turbo, high boost), this ensures the injectors aren't "leaning out" at the top of the rev range.
The Negatives
Fuel Pump Stress: Raising the pressure makes the fuel pump work harder. On an old, tired pump, this can accelerate its failure.
Rich Running (Non-Mapped): If your car is 100% stock, the ECU might struggle to adjust for the extra fuel, potentially leading to slightly higher fuel consumption or "over-fueling" at idle.
Not a "Magic" Power Gain: On its own, this won't give you 10 HP. It is a supporting mod designed to let other parts work better.
Relieve Fuel System Pressure
Before touching the regulator, the pressure inside the rail must be dropped. Locate the fuel rail at the top of the engine. Place a rag over the end of the rail and carefully depress the internal valve or slowly loosen the regulator seating to let the pressure bleed off into the cloth.
Remove the Retaining Clip
Locate the metal "U" clip holding the regulator in place. Using a small flathead screwdriver, gently pry the clip outward. Be careful not to let the clip "spring" away into the engine bay—keep a finger on it as it slides out.
Extract the Stock Regulator
With the clip removed, firmly pull the old 3.8 bar regulator upward. It may be tight due to the vacuum seal. Use a slight twisting motion to break the seal. Have your rag ready to catch the small amount of fuel that will escape the rail.
Prepare and Install the Bosch 4.0 Bar Unit
Inspect the new Bosch unit (0280160575). Ensure both O-rings are present and undamaged. Lightly lubricate the O-rings, then press the unit firmly into the fuel rail until it is fully seated and flush with the housing.
Secure and Test
Slide the metal retaining clip back into its grooves. It should "click" into place, locking the regulator down. Wipe away any spilled fuel. Turn the ignition to position 2 (without starting) three times to prime the pump and check for leaks. If dry, start the engine and perform a final visual inspection.
