Fuel Pressure Regulator - Mityvac MI8000 Benutzerhandbuch

SYSTEM OPERATION
Fuel pressure regulators are used to maintain
fuel pressure at a steady level, consistent with the
requirements of the engine. Automotive manufac-
turers employ different methods for controlling
fuel pressure. Most utilize a mechanical spring and
diaphragm style pressure regulator such as the one
shown in Figure 5. Mechanical regulators most often
utilize engine vacuum and/or pressure to vary fuel
pressure in response to immediate engine require-
ments. A vacuum or vacuum/pressure pump with
appropriate gauge is required to properly diagnose
these types of regulators.
Vacuum/pressure controlled fuel pressure regula-
tors are commonly mounted on or immediately
after the fuel rail, and inline with the flow of fuel.
When the fuel pump is not operating, the spring
causes the diaphragm to close so that no fuel can
pass. Once the fuel pump is activated, the pressure
it produces begins to overcome the spring force
and the diaphragm opens to allow fuel to flow. The
spring and diaphragm maintain a constant pressure
on the flow of fuel. This creates back-pressure in the
fuel system, which is commonly referred to as "fuel
pressure". The job of the fuel pressure regulator is
to maintain the "fuel pressure" at a level specified
by the vehicle manufacturer.
A vacuum/pressure-modulated fuel pressure regu-
lator is connected to the intake manifold by a small
hose. Vacuum from the manifold assists the spring
in opening the diaphragm. When a load is placed
on the powertrain, engine vacuum drops. This drop
in vacuum causes the diaphragm to increase the
resistance to fuel flow. The additional resistance
increases the fuel pressure to the injectors to com-
pensate for the higher fuel demand of the engine.
On forced-air induction systems (turbochargers/
superchargers), the boost pressure created in the
manifold functions the opposite of the vacuum pro-
duced in normally aspirated systems. Under boost
conditions, the pressure in the manifold causes the
regulator to increase fuel pressure, resulting in a
richer fuel mixture.
Page Number - 10

fueL pressure reGuLator

FIGURE 5:
PRESSURE
REGULATOR
Fuel Out
SERVICE PROCEDURES
Visual Inspection
1) Consult the vehicle's service manual to determine
if the pressure regulator is vacuum/pressure modu-
lated, and to identify its location.
2) Inspect the exterior of the pressure regulator for
fuel leaks, and the vacuum hose for visible damage
or cracks. Replace if necessary.
3) Disconnect the vacuum hose from the fuel pres-
sure regulator.
4) Check inside the hose for liquid fuel. If present,
replace the regulator. If not present, reconnect the
vacuum hose.
Diagnostics
5) Install a fuel pressure tester.
6) Start the engine and allow it to idle.
7) Disconnect the vacuum line from the fuel pres-
sure regulator.
8) Fuel pressure should increase 550 to 825 mbar
(8 to 12 psi) when the line is disconnected. No
change would indicate a faulty regulator, or leaky
or plugged vacuum line.
9) Connect the vacuum pump to the vacuum hose
extending from the manifold.
Vacuum/Pressure
Connection
Spring
Diaphragm
Fuel In
Form 824357