DPT701 Digital Pressure Tester User’s Guide_English Version_V2.00
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Figure 4-21 Sample Petrol Inj. System Maximum Screen
NOTE
The maximum reading is stored even if the display shows the actual reading and the stored
maximum reading can be read by pressing the right arrow key.
4.2.6 Common Rail Test – Low Pressure Circuit
This section illustrates how to test low pressure circuit with FOXWELL DPT701, the largest number of
failures are produced in the low pressure circuit.
4.2.6.1 About The Common Rail System
What is the Common Rail System?
The common rail system refers to the fact that all of the fuel injectors are supplied by a common
fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high
pressure. It is one of the most advanced diesel fuel injection systems.
One of the great advantages of this new system lies in the fact that the nozzles are controlled
electronically; so an electronic unit decides what the exact amount of fuel needed by the engine
is and sends an electrical signal to the injectors to open the nozzle. At that time the fuel pressure
in the common rail passes through the nozzles and goes into the cylinders. The name common
rail comes from the fact that the injectors are all connected to a common rail.
The injection system is divided into two distinct parts: the low pressure circuit and the high
pressure circuit.
The low pressure circuit is responsible for getting fuel to the high pressure pump in optimal
conditions of pressure, filtering etc.
The Structure of the Common Rail Systems
The low pressure circuit consists essentially of: fuel tank, fuel pump, filter, pressure regulator and
pipes.
Figure 4-22 Sample Common Rail System Structure
4.2.6.2 To perform low pressure circuit test
Checking the low pressure circuit is relatively easy, by checking the fuel pressure at certain points of
the system. To perform low side common rail, you need the following adaptors
