Ok. My s4 NA will NOT rev past 5000 rpm. it's also very sluggish. it has good compression ( 110-110-110 on the front rotor, 100-100-100 on the rear rotor), a new fuel filter, good spark on all 4 plugs. the secondary injectors are within spec resistance. i have good continuity on the plugs for them. I just got a new MAF from a junk yard and it's within spec. Anybody have any ideas?

well, it might help if you told us what it did when it got to 5000? does it just stop dead and sputter, or act like it hits a rev limiter, or what?

it acts like it hits a rev limiter.

Do you still have catalytic converters?

I once had a customer who had similar symptoms and it was a clogged converter.

He had an exhaust shop cut out the clogged cat and reweld it up with just one good cat and some straight pipe.

Maybe this is it??? https://www.nopistons.com/forums/pub...1047683473.gif

hrmm... could be the car has 214k miles on it and i am not aware of it ever having been changed. i will have to go see about getting a "test" pipe made up for it