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

Hi John

Will re-check the end were the filter is on pump again. And will perform
flow test.

Cheers
Barend.

You might have to put a fuel cooler on the return line.

Paul Lamar
--


Sounds like the fuel pump is vapor locking like the old Chevy's in hot
weather. A cooler or a larger surge tank.

Dale Davies