We got low sensitivity in FID after performance a P.M, (we changed all consumables) and performance back out of the column . The system is a 7890A (SSL-FID-ALS)
With low sensibility after P.M. I see you replaced many parts on detector but could you check again many steps below
+ volume sample injected correct? check your syringe or replace.
+ replace a new one liner and septa?
+ split ratio is it correct?
+ if you replace split vent trap, you can tighter the screw again.
+ gold seal
And very important you should be check split flow and purge flow.