Note: Before starting work on any part of the fuel system, read
the notes given in Section 2 of this Chapter
concerning safety precautions.
The only test of the fuel pump's and pressure regulator's performance
is to measure the delivery pressure, as described below. Note however
that if the fault occurs under a particular set of circumstances, for
example only in very hot weather, these circumstances should be
duplicated as closely as is reasonably possible when making the test.
First relieve any residual fuel system pressure as described in Section
Referring to Section 5 of this Chapter disconnect the fuel feed hose
at the fuel rail and connect a suitable pressure gauge between the hose
and the rail; BMW's own gauge is available under part number 16 1 500
Start the engine and allow it to idle while taking pressure readings.
Since fuel pressure is not related to engine speed there is no point in
running the engine any faster unless the fault occurs only at
higher speeds or the pressure regulator performance is to be checked. In
the latter case open and close the throttle sharply once or twice to
note the effect of the differing intake vacuum pressures on the fuel
pressure. If the pressure regulator is faulty, it must be renewed.
The pressure reading obtained should be steady at approximately 2.5
bar (36 psi) although some BMW service literature does mention a figure
of 2.2 bar (32 psi) at idle speed. If the reading obtained is
significantly lower than that specified, check the tank hoses and pipes
on the pump delivery side (Section 6), and the fuel filter
before renewing the fuel pump as described in Section
If the pressure recorded is significantly higher than that specified,
the pressure regulator and its vacuum hose should be checked (Section
12). If the pressure exceeds 4.7 bar (68 psi) indicating that the
regulator safety valve has stuck, the pressure regulator should be