1998 BMW 540i

Engine Performance problem
1998 BMW 540i V8 Two Wheel Drive Automatic 84000 miles

I replaced my valve cover gaskets this past summer because of oil leaking into the plug wells. I recently replaced all 8 spark plugs as well. Using the Peake code reader, the codes I am getting are " misfire detected, cyl. 5" & cyl 6, 7 & 8. Additionally, there is a " random or unknown cylinder" misfire along with " catalyst damaging" on cyl 5, 6, 7 & 8. I've swapped the ignition coils & the misfires are still on cyl 5 - 8. Also, the pre-cat O2 sensors were replaced about a year ago.

The check engine light flashes during wide open throttle beyond 3000 rpm & it struggles to rev past 4000 rpm - I took my foot off the accelerator after a while, thinking that I might do more damage if I tried to push it beyond 4000 rpms.

Thanks in advance.
December 29, 2009.

A flashing check engine light is not good. It indicates cat damage is occuring. Tell me all that has been done to the car, I need to know if the intake manifold has been off and if the PCV plate is original.

Dr. Hagerty
Dec 30, 2009.
The intake manifold hasn't been off & the PCV plate is original. I'm assuming that the PCV is the same thing as the CCV? Do I need to replace the vacuum lines & rear intake manifold gaskets? How much time is required for a weekend mechanic to do this?

Thank you.

Jan 2, 2010.
The job can sell for 5 or 6 hours and what will need to be replaced is not clear from cyberspace, but it might mean everything.

Dr. Hagerty
Jan 2, 2010.