I just bought the car from a dealer earlier this month (no warranty/my loss **** happens) with 55,000 miles on it.
The car drove fine for the first couple hundred miles then I got a misfire code for cylinder 8 I pulled the plug and it was fouled bad other spark plugs looked fine, did a compression check on all the cylinders everything it within spec. I checked the Air-Oil separator and the diaphragm seemed fine. Kinda stumped right now.

Any help/ideas would be greatly appreciated.

Worst comes to worse if anyone knows of any good shops in the Baltimore, MD area would be great.

 

Any codes?

 

I thought my diaphragm was ok too until further and much closer inspection. It had a hairline split that was barely noticeable. Lifted off manifold cover and intake valves were a horror story of sludge. I bought the car like this, unfortunately. Discovered 4 valves weren't seating. Cleaned intake valves as best I could. Installed a $14 oil can separator and within 2 weeks 2 valves re-seated themselves. The suction is crazy on these engines, but that's why they are so powerful.

 

rzmnco, did you ever figure out your issues, my #4 and #8 plugs a more fouled than the rest, and its running a bit rough.

Curious what the vacuum should be on the 4.5 and 4.8 turbos?

 

I have the nt530 and think diag…both have Aston Martin software..seems to cover most stuff…

 

Anyone have a possible answer to plugs 4 and 8 being more fouled, and showing more mis fire codes than all the other cylinders?