Aftermarket May 2022

MAY 2022 AFTERMARKET 31 discretion. Note my latter comment at the end. I will begin my story with the reported vehicle fault, rough idle, with a DTC reporting bank B rich mixture. I was not present when the triage took place. I did however have a lengthy discussion with David G, our diagnostic tech. This also raises the next most common mistake; Inaccurate forwarding of the customer’s comments to the workshop. This is where our story gets interesting and joins our list of the most common mistakes; When to say no. Critical criteria It was explained that the owner had removed the sparking plugs, both bank one Lambda sensors, all six injectors, and had swapped them over between bank A and B. This action did not resolve the problem. Before I continue with our investigation, let’s have a debate over the value of knowledge gained from the previous actions. This should not take long, as there is no diagnostic value. The critical criteria of any diagnosis is measurement and observation of control and response. Let’s review each of his actions. First, swapping the plugs over invalidates physical examination evidence. Next, exchange of the bank one Lambda sensors proves nothing, they could both be faulty, as well as wiring or a lack of control response by the PCM. There was no mention or knowledge from fuelling correction response from bank B either. The final piece of the puzzle is the most worrying and intriguing. The injectors were not subject to test and evaluation and were removed without the special puller. This allows for the stresses on the pintle housing to remain perfectly linear with the injector body. It is common for injectors to stick intermittently and may contain debris fouling as well as carbon on the pintle nozzles. Test do not guess I am going to enjoy this next simplification of diagnostic procedure; Listen to everything you are told, then ignore everything you are told, test do not guess, the actions you take are your way, or he takes the highway. Now for our way. David G began with a DTC scan confirming a rich mixture in bank B. There is the possibility of further non-confirmed errors, however David negated this by checking the fuel correction data from bank B which was 20%, so the PCM is listening and attempting to correct a genuine lack of oxygen in bank B exhaust. These words are carefully chosen as Lambda monitors oxygen not excess fuel; There is a subtle difference. Inspecting the plugs was a waste of time as they all showed excess soot, except for the fact we found some loose. Using our Pico scope kit, we conducted a simple cranking compression analysis. This is a useful yet simple test that proves mechanical rotational resistance against starter current consumption. The constant cranking current should be 3-3.5 x amp/hr battery rating confirming a reasonable compression resistance. Ultimate and definitive Our next test was the ultimate and definitive in cylinder test of cylinder pressures across the four-stroke cycle. This was conducted on both bank A and bank B for comparative analysis. Please refer to Fig.1 and Fig.2, both offering Pico images. The red line indicates TDC and BDC for clarity. This CAKA engine variant employs variable valve lift on the inlet with opening closing adjustment on both inlet and exhaust cams. You will note from both Fig.1 and Fig.2 that the exhaust open and closing events on bank B are very late compared with bank A. There were no DTCs for cam position error. I believe I am correct in assuming there is no cam position sensor on the exhaust bank. This is the only time in my review of the diagnosis that relies on opinion. Would this fault cause over fuelling on bank B? No, however let me conclude with another golden rule; Never proceed with a known fault requiring repair without corrective action. It was at this point that the highway option was implemented, as the owner did not have the funds for corrective repairs. Yes, they took it away. www.aftermarketonline.net Fig 1 The critical criteria of any diagnosis is measurement and observation of control and response ” Fig 2