BY Frank Massey This is the first time I have been tasked to repair a vehicle that has no obvious defects! A Skoda Fabia 1.2 tfsi 2016, a car I know quite well as I have just purchased the Monte Carlo version for my partner. Fitted with a range of engines 1.2 / 1.4 within the EA211 family, a very advanced turbocharged engine delivering remarkable torque with excellent fuel efficiency. The car in question had failed the MOT emissions test, just! If I recall correctly, CO% varied between 0.5% & 0.95%. HCs 70ppm, with lambda drifting around 0.97. Initially I was not involved with the assessment, however, I did provide some advice as to the diagnostic process. My first direct involvement was a global vehicle serial scan. I then examined the readiness flag registry in EOBD — all were in the green. This did not make any sense. This opened quite a debate in the workshop, with the other techs firmly pointing to a defective catalyst. I then had to explain the composition of exhaust cases pre-cat and how to determine the difference between incomplete 26 AFTERMARKET MAY 2024 TECHNICAL www.aftermarketonline.net A MONTH IN THE LIFE OF A VEHICLE TECHNICIAN Frank acts as a catalyst for debate in the workshop as he goes back to basics to help solve another technical mystery combustion HCs and rich AFR CO%. Cats do not produce CO above what would normally be expected pre-catalyst. Let us turn back the clock for a while and discuss four gas exhaust analysis. This is however a state-of-the-art direct injection high pressure system. Thirty plus years ago we could expect 0.5 CO%, 0.5 O2, 50ppm, 17% CO2. The golden triangle of tail pipe emissions, the goal was to match CO & O2 around 0.5%, This would ensure lambda one. So, this is NOT a catalyst fault. What comes next is so important with emission irregularities, fuel trim or correction, you MUST understand what the computer is doing and why. Fuel trim can be influenced by many external events beyond the ability to flag a DTC. Air leaks will produce additive trim, fuel pressure errors, injector delivery defects, discrete sensor range errors are but some of the possibilities. Long range trim at idle fluctuated between +3.55 and 0.0 with short term trim formation at 99.2. My next challenge was to carefully check all the critical specified
RkJQdWJsaXNoZXIy MjQ0NzM=