bmwcrocop

Brand New manifold installed and takes care of engine misfires for 90% of the time.

What else could be causing cylinder misfires?

It used to be 6 and 8 cylinders now its 5 and 7.

very strange

bmwcrocop

The pump and exhaust line have been check twice and in proper working order.

gsholz

Unfortunately there are many causes for cylinder misfires
- vacuum leaks (should have eliminated those with manifold change)
- coils, wires, spark plugs, ignition power supply
- injectors
- lack of compression
- camshaft timing

Believe the early 550 engines had some wear issues with timing idler gear. Did the shop eliminate that?

bmwcrocop

I think they have done all except camshaft timing and valve/valve chamber wear check.