FEBRUARY 2024 AFTERMARKET 25 Channel D could support a microphone input if chosen. Crankshaft rotation frequency is calculated via a mongoose serial interface, with channel ABC via the NVH 3 channel hardware. The vertical scope trace reports mass energy as milli g (gravity). The horizontal scope trace is separated by the various frequencies of vehicle operation. The catch is with the environment in which the test is concluded. Road vibration, throttle position, load, braking and steering will affect your results. Effect I conducted several drive cycles, each with differing drive conditions, and I have chosen exerts from various traces in presenting my evidence. My first shows smooth combustion events. Please refer to Fig.1, the first of three Pico screenshots. When mass (g) is shown in 3D and rotated, you can see each combustion event within the record length. It should be even in peak value and profile. Following careful selection of events throughout the trace shown by the shaded section of the record period the following anomalies were discovered. Please refer to Fig.2. The trace clearly shows omission of combustion contribution. I would draw your attention to the transfer of energy to the crankshaft E1 when combustion is unequal, resulting in the DMF having to absorb the anomalies. Now, please refer to Fig.3. The evidence appears to point to injector delivery imbalance, so prompting the only and correct action; Removal and a full injector bench test. For the injector report, please refer to Fig.4. The injectors were supplied via a nationwide discount chain, and had been refurbished by a diesel manufacturer. As a result of the comprehensive defects discovered, our future injector suppliers will be a local specialist. In conclusion the decision was taken to replace the injectors for genuine new units. Peter, our senior tech, commented that combustion noise reduced and engine performance dramatically improved. However, returning to work I was presented with comments from our customer that vibration was still present. We now arrive at the ultimate diagnostic option, customer opinion. The game continues! I promise to update via my topics if we progress further. Fig. 2 www.aftermarketonline.net Fig. 3 Fig. 4
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