July/August 2021

BY Frank Massey I concluded last month by suggesting we looked at several waveforms in order to understand and evaluate the behaviour of high pressure in common rail systems. However, just after submitting my draft, a perfect example was presented to our workshop. A VW 2.0 T5 with a fuel pressure deviation DTC. The vehicle would crank and run promptly, with normal drive characteristics up to 3500rpm. Its important to reflect on the comments in last month’s issue, with specific emphasis on priming and serial data evaluation. David specifically asked me to conduct the diagnosis and use the opportunity to conduct on-site internal training. We were informed of no previous work prior to the fault occurrence. My first focus was to listen to the fault 32 AFTERMARKET JULY/AUGUST 2021 TECHNICAL www.aftermarketonline.net CREST OF A WAVEFORM Frank jumps head first back into the world of waveforms to solve a fuel pressure problem symptoms and confer with Peter who had road-tested the T5. I was happy to accept the serial data provided to me by Peter. However, I must stress the importance of always confirming test results personally, not relying on opinion or previous non-confirmed results. I also opted not to attach the low-pressure gauge to confirm low pressure priming. So, I think I owe you a reason for not following my own process and previous advice. The short answer is experience of high-pressure waveform analysis. Now, the long answer. Test process My first test is an intuitive response to the Bosch EDC 17 system using Piezo injectors, as they often leak from the spill circuit. Firstly, disconnect the electrical connector, Fig .1