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4.3 High-pressure rail
4.3.1 Check pressure control valve (PCV) on high-
pressure rail
The task of the pressure control valves is to generate the
required pressure in the high-pressure rail and maintain it.
All three pressure control valves are installed in the high-
pressure rail and are connected in parallel.
Operating principle:
Located in the interior of a pressure control valve is an
armature, this is pushed down by a spring. The armature
presses a ball into a sealing seat and in doing so seals the
high-pressure side against the low-pressure side. In addi-
tion to the spring force a solenoid can exert a supporting
pressure on the armature.
If the pressure control valves are not actuated, i.e. the
solenoid is not energized, the high-pressure force pushes
in the rail against the spring force so that the pressure
control valves open the pump to a greater or lesser extent
- depending on the delivery rate. If the pressure in the rail
is to be increased, then in addition to the spring force, the
magnetic force also has to boosted. The pressure control
valves are actuated (energized) and thus closed, until an
equilibrium is reached between the high-pressure force on
the one side and the magnet and spring force on the other
side. Then they remain in an opened position thus holding
the pressure in the rail at a constant level.
Electrical test:
1. Detach electrical cable on PCV.
2. Connect digital multimeter to the two flat-type connec
-
tors on the PCV and measure the internal resistance.
i Do not measure internal resistance when PCV
heated up. Allow PCVs to cool down to ambient
temperature.
Internal resistance 4.2 Ohm
Tolerance ± 1 Ohm
If faulty:
– Replace PCV.
Hydraulic test:
The following three error options may occur:
• Slightly increased rail pressure at non-energized rail
PCVs during pump test.
The required test pressure during a measurement cannot
be reached despite an intact high-pressure pump.
During a pump test, test oil leaks from the PCV.
Error option 1
Slightly increased rail pressure at non-energized rail PCVs
during pump test.
Cause:
PCVs clogged up
Remedy:
1. Remove PCVs
2. Clean fine screen (1) of PCV in test oil bath.
! Observe tightening torque when installing PCV.
3. Install PCV again.
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