Hi Paul

   Hope all is well ?

   On stock 13 b s4 on both primary and secondary fuel rails you have
   fuel pressure regulators are both rated the same pressure and will it
   be possible for me to remove both regulators and run a single one
   adjustable regulator on the line that feeds back to the fuel tank ?

   Cheers
   Barend

   Yes. That is what most people do.

   BTW That makes me think somebody should record the fuel pressure
   1000 times a second with a data acq system. There may be something
   going on there we should know about.

   Paul Lamar


Hi Paul


I replaced the hp fuel pump with Bosch pump when the vehicle is cold my
fuel pressure gauge shows 4 bar [60 psi] as soon as the vehicle heats up and I
did around 25 miles the fuel pressure will drop down to 3 bar [45 psi] the pump
becomes noise I'll switch the vehicle off leave it for 10 - 15 min.
start the vehicle again and the fuel pressure will be back at 4 bar and
pump will be quite.

I have removed the fuel tank and flushed the fuel tank ( and fuel
lines) have two new in line fuel filters have a carter pre-pump pushing
at 0.5 bar pressure and 275 LPH to the surge tank( 2.5L tank) the surge
tank is flushed and cleaned the tank remains full at all times.

Which tells me my low pressure side is fine. The only thing I can think
off is that there is a concern with the fuel pressure regulators when
they start working they become hot and can not keep up ?

Cheers
Barend.

Is the new pump in the surge tank? Many in the tank pumps are designed
to be cooled by the fuel. I have never heard that about fuel pressure
regulators. One can buy a low cost infra red thermometer that can tell the
temperature of something by merely "looking" at it. The 2.5L surge tank fuel will heat up as hot fuel is returned to it by the pressure regulators.

Paul Lamar