April 2019

eliminating ignition and mechanical faults, it was time to take a look at fuelling faults. The problem on this particular vehicle meant that the cause would be isolated to one cylinder, this made the probability that it’d be a fuel supply issue to the rail less likely. With this in mind it makes sense to use a scope and carry out comparative checks on individual cylinders looking for anomalies that could be caused by a fuelling fault. Access to primary and secondary ignition was less than ideal due to the coil pack configuration so the ignition profile could not be used for fuelling evaluation. Injector supply, ECU control and circuit current were inspected across all cylinders and while there were small differences nothing was conclusive, until we took a look at rail pressure using the Pico WPS500x pressure transducer. Using this it was plain to see that upon injector number 4 being commanded to open and deliver fuel that there was little drop in rail pressure compared to the other cylinders. This definitely warranted further inspection so the injectors were removed and a flow test was completed in our test bench. Number 4 injector was found to be delivering significantly less fuel than expected. Bingo, we’d found our misfire. To scope or not to scope? Effective and efficient diagnosis is all about using the right tool, for the right test, at the correct point in your diagnostic routine, and as this vehicle has shown the oscilloscope plays a critical part in serving up the answers that whilst possible via other methods are often more time consuming to obtain. If an oscilloscope isn’t playing a major part in your day to day diagnosis then there’s no time like the present to blow the dust from it and start seeing the benefits that this amazing tool will bring to your workshop. www.aftermarketonline.net APRIL 2019 AFTERMARKET 19 EYEBROW www.aftermarketonline.net To find out more call Auto iQ on: 01604 328 500 _____________ To join AutoiQ’s online forum go to: autoiq.co.uk/ garageowners dƌĂŝŶŝŶŐ Θ ^ƵƉƉŽƌƚ Ƶŝůƚ ƌŽƵŶĚ zŽƵƌ ƵƚŽŵŽƟǀĞ ƵƐŝŶĞƐƐ KƵƌ ǁĞĂůƚŚ ŽĨ ŝŶĚƵƐƚƌLJ ĞdžƉĞƌŝŶĐĞ ĂŶĚ Ă ƚŚŽƌŽƵŐŚůLJ ŵŽĚĞƌŶ ĂƉƉƌŽĂĐŚ ǁŝůů ĚƌŝǀĞ LJŽƵƌ ďƵƐŝŶĞƐƐ ĨŽƌǁĂƌĚ͘ ǁǁǁ͘ĂƵƚŽŝƋ͘ĐŽ͘ƵŬ dĞů͗ ϬϭϲϬϰ ϯϮϴϱϬϬ Figure 2