Aftermarket November 2022

D id you know you can fix a misfire with a simple oil change? If you want to know how then please read on. I was recently tasked with looking at a mischievous Mitsubishi Shogun with a 3.5L V6 GDI engine. This engine a rare sight in the UK, which causes issues when trying to research the engine's configurations. The issue is a lack of available service information, as you will see. I was contacted by a local garage who asked me to investigate a misfire this vehicle exhibited when running at idle. They informed me the misfire was permanent and that they had already serviced both the ignition system and the fuel injection system. They also informed me that they had carried out a compression test and that the results were equal for all cylinders so, they were a little stumped as to what the cause could be. In their eyes, they had covered all the possibilities. I started by scanning the vehicle using our diagnostic equipment. A misfire for cylinder #5 was stored. I then used Mode $06 data in the EOBD menu, which records misfire data per cylinder. I could see there were 27 misfire counts for this cylinder, confirming the fault code to be correct. More importantly, no other cylinders were reporting misfires. This was a cylinder-specific issue. Next, I verified that both the ignition system and fuel injection system were operating correctly, as advised by the customer. This was done quickly using an oscilloscope, measuring coil and injector current. I could clearly see both ignition coil and fuel injector current events for the misfiring cylinder. I then carried out a relative compression test using the oscilloscope, and sure enough, all cylinders were equal and consistent. With this data, there was one other option; To connect a pressure transducer to the oscilloscope, remove the spark plug and install this pressure transducer into the cylinder to measure real-time pressure, plotted over time. If there were any valve train issues, we would likely see them using these pieces of equipment. 22 AFTERMARKET NOVEMBER 2022 TECHNICAL www.aftermarketonline.net SON OF A SHOGUN A misfiring Mitsubishi Shogun provided Ryan with his latest challenge BY Ryan Colley, Elite Automotive Diagnostics Fig.1 Fig.2