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


  Re low fuel pressure,  there is a very small gauze filter in the inlet
 of most Bosch fuel pumps, which does not take much to clogg up but keeps
 out bits from the pump
 if the pump is noisy when hot i would think it is caviating,
 probably due to the hot fuel and a low pressure on the suction side.
 John Burey

Hi John


That sounds correct to me as the pump starts to become noise I'll poor
cold water on the surge tank and pump and the noise will go away. Going
to fit fuel cooler and feed back once completed.

Cheers
Barend.
 --


Check that filter in the inlet of the pump, if you have a lift pump
supplying fuel to the HP pumps the temperature of the fuel should not
matter, really sounds like it is not getting enough fuel, try the total
flow output without the pressure regulators, should be able to maintain
about 60 psi at least 200 lph without noise or bubbles into a container,
be CAREFUL hot fuel spraying around and a static spark and WOOSCH!!!:'(
 John Burey