2005 A8 D3 4.2 (BFM) - Low MPG

[steamship]

Originally Posted by MatthewH

Hi, the catalytic converter is something I'd considered. I'm not sure how that could be tested though. It passed MOT with no emissions problems last time around if that makes any difference. It did originally fail on emissions but after replacing both leaking flex pipes it passed (didn't know a leaking flex pipe could cause an emissions failure at the time as it's after the cat)

The pre-cat O2 sensors have just been changed (finished today) as that was the only thing left that I could of, but they don't seem to have shown any improvement. Post-cat sensors are still originals as far as I know.

Thanks

I came across this site about catalytic converters and some checks you can do, including exhaust back pressure. However, from what you've posted so far and what it says on this site, this may not be your problem. The site is as follows:

http://www.aa1car.com/library/converter.htm