fast efi problem

my battery is grounded to frame and power going to starter, i have a ground from engine to firewall
the fast ecu is wire directly to battery and no other components are hooked to battery.
it has worked for 2000 miles this way.
on my handheld it shows a rms value, from what i understand this detects interference and if the number gets above 10 then there is a problem. so far the highest number ive seen is 8 but usually 0