BMW 4.6 is poor acceleration and hesitation

[bcredliner]

Originally Posted by Aman

Thanks for the info
One thing I forgot to mention is that I had to take the car for a yearly emissions test (required by law) and it passed with low emissions. Lambda value on emissions test was 1.0, CO and HC values were low - this was even before the blocked (left) cat converter was replaced
But then again, maybe the tester put the emissions testing probe up the right exhaust (good side) not the left one (faulty side), I don't think they test both tailpipes on V-engines...

I think you are right not to consider the emission test

O2 sensors, especially the pre cat sensors, should be replaced at 60-70,000 miles to assure your mileage and/or performance doesn't take a hit. I still think you should have them tested before purchasing sensors but even before they go bad the performance declines and can be an intermittent or continuous decline to point of failure.