BMW 4.6 is poor acceleration and hesitation

[TerminatorX5]

here are my values when the cyl 5 was out of whack... for your reference point. mine is 2006 4.8iS - which is N62/S engine... your cyls 6 and 8 don't look right... the cyls 5 and 7 are off but not by much...

the cyl codes might be secondary to the fuel pressure at one bank at the fuel rail... check the pressure, see if it is a good number...

[bcredliner]

Since the issue is only showing on one bank, spark plugs have been replaced, coils are good, air is getting in an out, and fuel pressure is OK on the other bank, I think we have narrowed it down to fuel mixture controls that are on 1 bank.

I don't recall that you replaced any O2 sensors so that could be the problem or there could be a vacuum leak on that bank that has not yet been discovered. There are other possible causes but IMO, not as likely. Next step, I would confirm the O2 sensors on that bank are working properly though either possibility could have been the core cause.

[Aman]

Originally Posted by bcredliner

Since the issue is only showing on one bank, spark plugs have been replaced, coils are good, air is getting in an out, and fuel pressure is OK on the other bank, I think we have narrowed it down to fuel mixture controls that are on 1 bank.

I don't recall that you replaced any O2 sensors so that could be the problem or there could be a vacuum leak on that bank that has not yet been discovered. There are other possible causes but IMO, not as likely. Next step, I would confirm the O2 sensors on that bank are working properly though either possibility could have been the core cause.

Thanks for your help
Does code 26 multiple fuel trim 1 mean it is to do with bank 1 (cylinders 1-4)?
Does code 29 additive fuel trim 2 mean it is to do with bank 2 (cylinders 5-8)?
Does that mean there is a problem with both banks, eventhough cylinders 1-4 are running with smooth running values of 0.00?
Why would code 45 catalytic converter 2 be showing up? Catalytic converter bank 2 (cylinders 5-8) was the one that broke down and caused a blockage last time (now replaced with new cat)
What is he best way to test oxygen sensors?
Last time the scanner was plugged in I remember one pre cat oxygen sensor switching between 0.2 and 0.8, the other was switching between 0.1 and 0.8 (at idle)
Is this enough info to test the oxygen sensors?
Are the post cat oxygen sensors important in the running of the engine?
The guy is coming round today to do another live test of engine, just need to know what to check and look out for
Thanks

[Aman]

The other thing I should mention (this happened for the first time
Yesterday), is the when I started the car, it started, then stalled
Second time I tried starting it ran then immediately stalled
I think it was the fourth attempt that the car started and continued to idle.
This has not happened before.
This occurred after the engine light came on yesterday.

[Aman]

I was looking around in engine bay and I noticed that towards the front of bank 2 (left side of car, cylinders 5-8), there is a platic pipe with no end to it
It is at the bottom of the attached photo
Should it be like this? Any idea what it is for?
My mechanic couldnt make it today, but he is coming first thing in the morning (in 13 hours time) to scan car for codes, as check engine light came on again today.
Check engine light is coming on every day now (even though it was reset yesterday)
Cheers

[TerminatorX5]

that is a vent tube, should be like that, it is not a problem...

[Aman]

Originally Posted by TerminatorX5

that is a vent tube, should be like that, it is not a problem...

Thanks

[bcredliner]

O2 sensor operating parameters. BMW Oxygen Sensors & Emissions - Facts & Repair Advice

The post cat O2 sensors are emissions only-have nothing to do with engine performance

[Aman]

Originally Posted by bcredliner

O2 sensor operating parameters. BMW Oxygen Sensors & Emissions - Facts & Repair Advice

The post cat O2 sensors are emissions only-have nothing to do with engine performance

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...

[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.