May 2021

BY Frank Massey I left part three, and its subject, the problematic AUDI A3 1.8 TFSI, somewhat up in the air last month. It was written in real-time, responding to the test already carried out. We were faced with a noticeably short list of possibilities. There was no obvious sensor input error or deviation. GDI pressure was low, but under PCM control. Fuel trim rich correction was only present when running on GDI injection, i.e., start up, warm up and full load. The injectors were tested, so the remaining conclusion was a PCM software/ hardware error. However, we were still not sure. Experience directs me to discount this option as highly unlikely. However, as we have access to a SEAT LEON FR (well, I do, it’s mine!), we opted to substitute the PCM coding 1 key only to enable engine run. The result; no change whatsoever, and the only evidence of fault we have is Lambda reporting an oxygen deficiency (rich) mixture and the PCM with up to -30% trim. Fuel pressure was holding, so no dribbling injectors. The only route that fuel could enter the combustion chamber is through the injector. Retest In my absence, David G removed the injectors for re-test. In Fig.1 you will see the ASNU bench showing the new injector at 85ml delivery. Wow! The new injector only delivers 85ml against the three original injectors at 110ml. Upon checking the Audi database, we found there was a later part number, so four more injectors were bought and tested. All four delivered 85ml. We were confident they were correct, and they were fitted, awaiting the inevitable software update. To our total surprise the vehicle ran perfectly with no trim correction and increased GDI pressures. I spent this week researching injector application and discussing specifications with Phil Ellison at ASNU. Findings Here are the findings and answer to the fault: Original injector part no 06L 906036L – static pintle flow 1200ml IST new injector fitted to number 1 cylinder, 06L 906036AC -static pintle flow 830ml 30 AFTERMARKET MAY 2021 TECHNICAL www.aftermarketonline.net SETTING THE BAR HIGH Frank’s epic saga of the Audi S3 reaches its exciting conclusion, we hope! Complete new ST latest update 06L 906036G - static pintle flow 830ml Penny dropped guys? Some clown had fitted high-flow 2.0 litre injectors in the 1.8. This means that the Lambda was telling the truth, the PCM was in closed loop applying correction, and the GDI pressure was reduced in response. On reflection where did we go wrong? Look at item 2, from part 2 of my assessment; “A physical or hydraulic injector fault.” I had the answer then, written one month before this conclusion! So, while being critical over the parts fitted previously without a detailed evaluation, my error was not questioning the possibility of incorrect injector fitment, or checking flow rates at the first time of test. I found this challenge invaluable as a reminder not to relax proven procedures and attention to detail no matter how improbable it may seem. Gems So, what other little gems did we encounter with our Christmas pudding? “AUDI A4 TDI, no runner hard DTC, reference voltage bank B short to ground.” Like many vaguely descriptive trouble code messages, it always helps to consult the wiring schematics. “Circuit B 5volt reference feeds the crank angle sensor, EGR, and rail pressure sensor.” True to form the voltage was low and unstable. There are a couple of options here. You can unplug each component in turn, or cut the circuit close to the PCM, and then wait to see if it pops back up. David G chose the first option finding the problem with the EGR valve. Referring to Fig.2, this image shows the EGR internals with water ingress. The next story brings a smile to my face. It concerns an Audi A6 3-litre, diesel suffering turbo failure. It ran with excessive noise from the turbo. It had just been serviced by its owner. Having exposed the turbo, we could see severe FOD damage to the compressor turbine (cold side). The debris was a small plastic strip. Then Peter B remembered seeing damage to the support PART FOUR Fig 1 Fig 2