May 2019

It’s not possible within the scope of this article to do justice to all of the information available from this waveform, as the Editor only allows me to write 1,100 words per month. How stingy is that? However, there is just enough room to highlight a couple of important points that will play a key part in diagnosing this vehicle. Knowing where to look and not over-analysing this waveform is the key to timely diagnosis, and there were a couple of key areas that we’re plainly incorrect. Peak cylinder pressure on this vehicle was found to be lower on cylinder 4 than the other cylinders by 25psi. This was not highlighted by the compression gauge to due to its non- return valve. Another key clue was the point at which the exhaust valve opened. The exhaust valve opening on cylinder four was found to be advanced by 17 degrees but only on that cylinder. This could clearly be seen (at point 5) by using the cursor feature in the Pico software. Once the pieces of the puzzle had been bought together it was clear that there were only a couple of scenarios that could give us these results. We decided that a physical inspection was justified and this confirmed that the exhaust tappet was tight on cylinder 4 to the tune of 12,000. (.0305mm in new money). This was clearly the cause of our sick engine. Diagnosis with a pressure transducer can often seem like witchcraft to those that aren’t familiar with the technique, but in reality like all things ‘diagnosis’, the fundamentals can be learned by anyone, and mastery attained with some practice. There’s one thing for sure. Understanding oscilloscope fundamentals is the key to reducing your time to diagnose. Meanwhile, accessories such as pressure transducers are as essential as a spark plug socket if you want to keep your nose ahead of the competition, which is never a bad thing. www.aftermarketonline.net MAY 2019 AFTERMARKET 19 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 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