June 2019

non-stop activity with all other cylinders at zero. Now this is where it gets a little more interesting as this tech took a route that was out of step with the other contestants. He didn’t go straight for the injector He requested a 2000 amp clamp and proceeded to carry out a relative compression test. Cranking speed was good and all current draw was equal. He noted that the likelihood of a mechanical fault would be low Next a spark gap tester was used. While secondary ignition could have been scoped it would have sapped time due to the system this vehicle used. It was a sensible choice given the circumstances. Spark output on cylinder 4 was found to be sufficient to consider the problem was elsewhere At this point the technician was swiftly ruling out the good (or at least less likely options), and honing in on the possible causes remaining. Just one thing. He only has eight minutes remaining. An oscilloscope was now used. A low current clamp was applied to the common injector power supply while the switched side of the injector was inspected on each of the four cylinders. There was much pondering, timebases and vertical scales we’re changed while all elements of the various channels were compared between good and bad cylinders. All injectors (including cylinder4 with its fault code) were clearly being switched on and off, so why the misfire? As a judge I’m not sure what was louder. The cogs going round in the tech’s head or his heartbeat! We had 180 seconds left. Would this guy find the fault? With a sudden burst of action the pondering ceased and more tools were requested A pressure transducer was applied to the fuel rail (manifold injected vehicle). A timebase was selected so that one cycle of all injectors was displayed. This test was the key to the fault on this vehicle! By comparing injector current and rail pressure it was clear to see that rail pressure did not drop as number four injector was commanded to open. The fault was found. It had to be a blocked injector. The technician requested tools to move the injector to another cylinder for confirmation, but time was up and the task was over A job well done I’m sure you’ll agree that to complete that range of tests in unfamiliar surroundings, with tools that aren’t your own, in 20 minutes while being observed by me is no mean feat, so hats off to that particular technician. Here’s a fact for you though. It’s within your grasp as well. I’ve been teaching the skills required for accurate and timely vehicle diagnosis for a very long time, and there’s just two things you need to achieve the skills articulated in this article. These are the will to learn and a little practice. Get started on those and whether you want to become a Master Technician, win a competition, or just increase your competency in the workshop, you’ll be set for success. JUNE 2019 AFTERMARKET 23 EYEBROW www.aftermarketonline.net If you’d like to learn how to improve your diagnosis skills then call John on 01604 328500. Auto iQ have a complete technician development programme designed to help your technicians be the best they can be. _____________ To join AutoiQ’s online forum go to: autoiq.co.uk/ garageowners