Diagnosing CRD faults with a Pressure Tester
One result of the increasing market share of diesel vehicles is that we are seeing more and more pressure related fault codes, with the high replacement cost of CRD components it is important to make an efficient accurate diagnosis. As always the first step in any diagnosis is to record and clear, and operate vehicle until fault codes reset. Symptoms and fault recordings indicating a malfunction in the fuel system require tests of the low-pressure and high-pressure circuit prior to component replacements. These tests prove helpful in the majority of cases, even when an ECU shows no fault entries at all despite poor engine performance. Determining which part of the system to test first – the high – or the low-pressure circuit – depends on the nature of the problem and on accessibility to the fuel system.
CRD Low Pressure / Pre Delivery

The Low Pressure (Pre Delivery) supplies filtered fuel to the injector pump. The lift pump (transfer pump) is typically located in the fuel tank (submerged electric pump), on the back of the injector pump (gear pump), or both in tank and on injector pump. Testing the low pressure side is imperative as faults in the low pressure side cascade to the high pressure side. Testing the fuel pressure after the fuel filter before the injector pump will rule in / out faults -Refer to manufactures specifications of give us a call. Also it is a wise idea (time permitting) to test the pressure before and after the fuel filter to rule out flow / blockages.
CRD High Pressure / Forward Delivery

The High Pressure (Forward Delivery) system supplies pressurised fuel to the Injector Rail typically with a maximum pressure of 1600 – 2000 Bar (23520 – 28400 psi) and At Idle 300 – 400Bar (4410 – 5880 psi) The Test the pressure between the injector pump and or at the fuel rail.
High pressure pump only test. It is best to take the reading directly from the pump. Eliminate the rail completely. Some manufactures have mechanical or electronic pressure relief valves in the rail that can fail can cause low pressure readings at the pump.
CRD Low Pressure / Fuel Return

Test the pressure between the return collection pipe and fuel tank.
CRD Leak Fuel Quantity

Performing a leakfuel quantity comparison test is carried out by disconnecting the return line to the fuel injectors and installing piping (Piezo injectors require an additional special adaption with pressure-holding valves that maintain a pressure of ten bar in the return lines). The quantity-measuring device is directly hooked up to the return connection of the injectors. When removing the return line on the injector, be careful not to damage the connection. Disconnecting the line to the fuel injector also requires proper means of doing so without damaging it. Once the return-quantity measuring device is hooked up, the engine is started and the return quantity is measured on all cylinders. Here it is important that the quantities of the individual cylinders increase at the same rate. Any difference higher than that requires the injectors with the largest return quantities to be either repaired or replaced.
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