July/August 2020

have enough energy to produce a spark for good ignition? In Fig.2 You’ll see a secondary ignition waveform. Looking at the firing KV at Point B, for sufficient energy to initiate a spark, comparing this on all cylinders and looking for anomalies is a great place to start. Should I have one that’s too low or non-existent, then I’ll be checking powers, grounds, and primary switching at the coil, before considering the possibility of a defective coil. All good? If that’s a resounding yes then let’s take a look at fueling. ‘Those in the know measure flow’ are wise words, and I’ve used flow testing to find many fueling faults. In this instance though, we’re looking for a test that gets us in the ballpark to assess if fuel is being injected. You have a few options. You could: Opt for a visual inspection of the plugs. Are they wet? Use a gas analyser pre/post cat. Do you have HC? Scope injectors and fuel rail pressure – Does the rail pressure drop while injectors actuated? No HC, dry plugs, lack of injector actuation and questionable fuel pressure, all give you diagnostic direction and highlight additional testing is required on your fuel sub system. Found your way? All being well, your diagnosis now has direction and a path to more specific faults in a given sub-system. Assuming reasonable accessibility and a little practice you’ll often be able to complete those tests in around 30 minutes(ish), which will leave you with at least another 30 minutes to further explore any issues before presenting your findings to your workshop manager. One thing’s for sure; Having a structured approach to your fault finding, looking for diagnostic direction, with a few familiar tests up your sleeve will reduce your diagnostic time and increase your confidence exponentially. Want to know more? If so then take a look at next issue's article where I’ll be taking a look at some actual non-start issues with detailed test results. JULY/AUGUST 2020 AFTERMARKET 25 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 Fig.2