Fast ram not being detected in amiga 4000

[amiga4000freak]

hi to all

I have a amiga 4000 rev b and its not detecting my fast ram.
I have played around with jumpers and nothing happens would it be best to use a zorro 2 card with 4meg of ram or do i invest in a zoram from amiga kit instead so it will be using zorro 3 which is faster. Im only using the amiga for games any suggestions would gratefull

[amiga4000freak]

hello

yes i have tested two different ram chips an it only detects 2 meg chip ram