March 2021

BY Frank Massey W here were we? I’m wondering that myself, so I will begin with a recap of part one, along with an honest critique of what has gone up to this point. So far, the following parts have been replaced; Four spark plugs, four ignition coils, high pressure fuel pump, and #1 high pressure injector. The phrases ‘dirty washing’ and ‘public’ come to mind. Despite what I always tell you, these parts were replaced as a result of a reaction to the symptoms and not as a result of thorough data analysis. We understand, with confidence, that the fault is due to a lean fuelling condition, but we do not understand the cause. I do, however, have a high degree of confidence it is not a hydraulic-mechanical injector fault, following the ASNU bench test. David G and I took a step back to review our approach and plan a way forward. Using VCDS, we elected to monitor critical events from crank start through to hot idle. Referring to Fig.1, please note there were no initial issues during at first, then quite suddenly after 30-50 seconds, you will see what happened, coinciding with the onset of combustion error. High pressure is a touch low though. Moving onto Fig.2, please note the drop in high fuel pressure. At this point it is sitting at 45bar. This is not correct, so why do request and actual match? Has the PCM in error calculated this as the correct value? Or is it an incorrect load value from a sensor, wiring or environment? Maybe it is a PCM internal fault? Experience generally convinces me it is not the PCM however. Evidence Let’s discuss the evidence, while also keeping an eye on the camshaft timing which I alluded to in part one last month. From cold, the exhaust camshaft increases its lift by approx. 0.6mm and adopts an advance angle of 35°. The inlet remains at zero and does not have any lift function. As a point of interest, you should hear a distinct click from the cam housing when full exhaust lift ends together with a sudden reduction in open angle. Consult data frames to see what I mean. This occurs normally after approximately two minutes. Please also note the change in exhaust cam timing to 2.8° actual 4.0° specified. The inlet now adopts an angle of 15° actual and specified. Moving onto Fig.3, the data displayed shows values from the engine mid-way through the warm-up cycle. The engine is still fuelling from the high-pressure system. The high pressure has now deteriorated to a mere 35bar, and 50% of the nominal expected value. The lean combustion problem is now extreme with misfire count increasing dramatically. We now reach Fig.4. Finally, after approximately 10 minutes, the PCM reverts to port injection. This can vary dependant on environmental temperatures and engine 22 AFTERMARKET MARCH 2021 TECHNICAL www.aftermarketonline.net SETTING THE BAR HIGH Frank continues the saga of the Audi S3 that began last issue, and he really gets into the nuts and bolts of the problem this month PART TWO Fig 1 Fig 2 Fig 3 Fig 4 Fig 5