3 Series E30 325i (M20) SAL
13 31 ...
Notes on fuel pressure check (reference pressure: intake manifold pressure)
Feature of this version with intake manifold pressure:
The connection for the vacuum hose of the fuel pressure regulator is located in the intake manifold after the
throttle.
Test precondition:
The correct fuel pressure regulator is fitted.
-
Using the EPC, check whether the fuel pressure regulator suitable for the car is fitted:
Connect test adapter,
refer to 13 31 029.
Description of operation: fuel pressure regulator
Depending on requirements, the fuel pressure regulator regulates a low or high fuel pressure. This requirement is set
with the help of the pressure regulator.
Depending on the engine's operating state, less or more fuel is needed:
-
at idle speed, less fuel
-
at full load, considerably more fuel.
The injection rate is precision-adjusted by means of the injection time; the injection time is controlled by the DME.
The partial vacuum in the intake manifold serves as engine load information for pressure regulation. The diaphragm of
the pressure regulator is actuated with this partial vacuum.
A partial vacuum builds up in the intake manifold during idling operation or in overrun mode. Depending on the partial
vacuum value, the fuel pressure decreases starting out from the nominal value. The nominal value is stamped in the
fuel pressure regulator housing.
At full load, the partial vacuum in the intake manifold is approximately equal to zero. The fuel pressure regulator
regulates the fuel pressure to the nominal value stamped in the housing.
Description of operation: fuel pump
The control function of the fuel pressure regulator must be ensured in all operating states. The fuel pump must
therefore always be able to generate a higher fuel pressure than the pressure regulated by the pressure regulator.
Description of operation: fuel return line
When the engine is at a standstill and the ignition key is in position 0, the fuel return line after the pressure regulator is
at zero pressure.
Description of operation: pressure retaining function
The pressure regulator closes when the engine is at a standstill and the ignition key is in position 0. The fuel pressure
in the delivery line is retained over an extended period. A non-return valve closes in the fuel pump. These measures
help to retain the fuel pressure in the fuel system. Extended starting times are thus avoided.
Complaint: drive characteristic faults, lack of power
-
Run engine at idle speed and measure fuel pressure.
-
In order to simulate "full load" state:
Disconnect vacuum hose from fuel pressure regulator and measure fuel pressure.
The measured value must increase by 0.4 to 0.7 bar depending on the engine. Note down measured value.
RA Notes on fuel pressure check (reference pressure: intake manifold pressure)
BMW AG - TIS
26.01.2013 11:33
Issue status (12/2007) Valid only until next DVD is issued
Copyright
Page - 1 -
