October 22, 2019 at 5:36 pm #99294bn1990Participant
I am trying to diagnose a problem with my car and would like some assistance if possible. Generally the car starts well in the morning after sitting all night. Various times throughout the day it will stutter initially and then die right after starting it. Only way to get it to start is to hold the gas pedal down or pump it until it starts. After that it will run rough and then eventually smooth out and run. The car doesn’t feel as responsive as it was when I bought it within the past year. I just went over 100,000 miles this week.
I have been using VCDS software from Ross-Tech to monitor the engine fault codes and the fuel trim values while running. After clearing the codes and then running for a while (maybe a week) the long term mixtures values for both banks are around -30%. The short term value after the engine is warmed up is usually around 5-8%.
It was also suggested that I monitor the O2 sensors and I have been watching the following values:
Current of O2 sensor bank 1 sensor 1: 1.068 Lambda/0.055mA
Current of O2 sensor bank 2 sensor 1: 1.071 Lambda/0.059mA
I have watched the YouTube videos that you posted about fuel trims (Secret of Engine Problem Diagnosis – Fuel Trims Pt.1 and Pt.2). They are the best explanations that I have seen so far but they primarily covered lean conditions and and have the less common rich condition. I am not a mechanic but I am trying to lean and hope to save some money by diagnosing this myself and hopefully replacing any required parts if possible.
I am seeing P0172 and P0175 codes consistently on both banks. I know that a very common problem on the 4.2L V8 in this model is failing high pressure fuel pumps. It seems less likely that both pumps would fail at the same time even though of have been told that I should probably replace them. I would expect one to fail and then only see the rich condition on one of the two banks; not both. I am fairly comfortable replacing the pumps myself but before spending the money on the pumps I would like to see if anyone has any thoughts on what else it could be. I know that leaking fuel injectors can cause a rich condition but both banks?
I am also receiving a warning about the oil level being too high and that I need to reduce it. This has occurred since I had the oil changed by a repair shop while they were trying to diagnose this issue. The starting problem were occurring prior to the oil change and the high level warning.
The repair shop replaced spark plugs, air filter and cleaned the air intake. The starting problems persisted after that.
With VCDS I am able to monitor any values that could be helpful. What else should be investigated at this point?
My car just went over 100,000 miles.
Thank youJuly 26, 2020 at 7:03 pm #2331452012AudiA8Participant
I am having the same issue with my 2012 A8L. 113k mikes. Did you ever get it resolved?
My gas is smelly. Was yours too?August 4, 2020 at 3:57 pm #236444adminKeymaster
Did you reduce the oil level? – It was interesting that it was high enough to fire a warning, that would not happen if it was just a little bit up. Theoretically it would be high enough for one of the rotating parts in the crankcase to hit the surface of the oil and explode oil everywhere including the cylinder walls, beyond the capacity of the oil rings to cope. I’ve never heard of anyone filling the sump that high but …………..
Many years ago there was an engine with A sloping cylinder that had a persistant problem with the internal flywheel spinning oil up into the cylinder – caused problems. Won’t cost any financial paid to correct the oil level and see what happens. Might take a little while for the rich situation to correct.September 24, 2020 at 3:44 am #262071Naughty NateParticipant
Sounds like leaking fuel injectors, especially if you smell gas as the person above stated. While the car sits overnight, the gas leaked from the rail and seeped slowly down past the pistons, so the combustion chamber is clean when you start in the morning. But after you run it and stop, there is still fresh gas leaking into the cylinders and flooding them, making it hard to start until it finishes leaking down.
By pushing the gas pedal down all the way before trying to start, the PCM will cut the injector pulse, and so it may fire up without flooding it by adding extra gas. Try this next time it’s warmed up and won’t start- pedal down all the way then try starting. If that helps it start, then it’s the injectors.
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