Bosch Motorsports 5 Bar Fuel Pressure Regulator - PeachParts Mercedes-Benz Forum

Blown_M104 · #1 12-28-2005, 10:43 AM

For those running a Supercharger or Turbo on your stock NA engines you might want to consider this...

Even after my recent installation of a Piggy-back ECU (see previous thread for details) I was still running lean under WOT and heavy boost. The logical next step was to increase the fuel injector size. Finding the correct two-nozzle injector for this M104 motor with a higher flow rate proved to be difficult and if I had found larger injectors they would have been expensive. What I found was a nice, much less expensive, compromise…

Bosch Motor Sports and Neuspeed both make a 5 Bar Fuel Pressure regulator that is a direct replacement for the stock 4 bar unit commonly used on the Mercedes engines ($79 US). With 5 Bars of pressure behind the injectors they flow considerably more than with the stock 4 Bars. 5 bar is 25% more than 4 bar and so the injectors now provide a proportionally larger amount of fuel with the same firing time.

With the 5 bar FPR installed I ran the Apexi back to a –23% offset when under low throttle position conditions. (If you don't have a way to re-map your A/F ratio don't go to this 5 bar regulator, you will run way too rich at idle and under partial load conditions.) Then under heavy throttle I ramped in increasingly larger positive multiplier values to the MAFS signal all the way up to +49% at +6000 rpm. The +49% added to the apx 25% increase in flow of 5 bars over 4 bars totals about 65-75% more fuel than stock.

This FPR is typically used in Turbo kits for the Audi A4 but is a direct fit for the stock 4 Bar Bosch unit Mercedes uses.

Have fun with it!

http://www.bosch-motorsport.com/de/aktuatoren/pdf/fuel_pressure_regulators/mini50.pdf

http://www.supremepowerparts.com/category/engine/engine-neuspeed-fpr.html

2phast · #2 12-29-2005, 08:22 PM

Running a higher fuel pressure will throw a CEL, how did you deal with that issue?

Blown_M104 · #3 12-30-2005, 12:03 AM

Thanks for the question. The CEL is not a problem on my 300 series in that the car does not have a CEL. Only the California versions of the 300 and 400 got the CEL in 93; it is however on all 500 models as you know. If I had one you're right it would be as bright as a Christmas tree.

PS
Love your 500, beautiful car.