July/August 2021

remove the spill hoses from the injector, then crank the engine. Observation should confirm no spill whatsoever. So, with a good result let us move on. I placed the vehicle battery on charge prior to checking cranking evaluation, once this was confirmed I could begin attaching my Pico to the rail pressure sensor (RPS). I always choose a relative test connection, with both signal, centre pin, and ground taken from the RPS. A time base of 50 seconds sweep time and 5-volt range with 10m/s sample rate conclude my set up. With scope running I start the engine, allowing to idle for several seconds then opening the throttle to increase engine RPM as much as the software allows. Lifting off the throttle allowing to return to idle then switching off, with the engine static turn on ignition to maintain a RPS output signal. My first observation is rise time from 0.5volts/zero pressure to 1volt /260 bar. This should occur from 180m/s up to 350m/s. With the pressure rise close to 350m/s, it is logical to assume priming and fuel leak-back are normal. The prime purpose of any logic process is to minimise time without compromise in the accuracy of results. Crank start results were spot-on, as was the smooth rail pressure at idle, which confirms the smooth mechanical action of rail pressure actuators. Additional observation was taken from the diesel regulation valve (DRV) which should have a nominal value of 17% (see Fig.1). This is especially important as any correction will affect the control duty value. The next test is what I call full system pressure or proof pressure. I did warn of potential damage if not familiar with the system hydraulic or electrical control. Firstly, disconnect the volume control valve (MPROP) mounted on the HP pump housing, this will not affect pressure regulation for test purposes (see Fig.2). With the MPROP disconnected, system pressure has sole control from the DRV. Bosch switch ground on to control duty. It is vital to 34 AFTERMARKET JULY/AUGUST 2021 TECHNICAL www.aftermarketonline.net confirm which of two wires is the PCM control, prior to attaching a parallel connection to a suitable DMM probe. With the engine set at 2,000 RPM and stable, connect the parallel probe to a suitable ground and hold it there until well after the engine has stopped. The effect of this action completely closes the DRV which should result in maximum system pressure, i.e., 4.5 volts at the RPS, with 1,650 bar pressure. The rise time to 4.5volts at 2,000 RPM should not take longer than 180m/s. The vehicle under test initially looked ok at 180m/s, I must stress the importance of always confirming test results personally, not relying on opinion or previous non-confirmed result ” Fig.2 Fig.3 Fig.4