after starting my 94 miata the LC1 works great - the signal in MS is the same as on the LC1 gauge, it reacts the same in whole range. but after I drive for a minute (or the car warms up) the signal is distorted - it'a best visible with throttle off: the LC1 gauge shows AFR 22, but the gauge on my laptop shows about 16-18. After turning the engine off for 5 min. its ok again but after a minute drive the same error happens. The signal to MS is ok for sure, because after changing outputs from LC1 the lc1 gauge works great on both of output and MS gauge has the same error on both outputs.
So my guess is GROUND PROBLEM
I don't have a stock ground connector (under TB) on my 94 miata. Everything worked great wit the ECU ground connected here (it was there when I bought the car):
but it seems that LC1 needs a more stable ground. I tried to get the ground from the chassis, from the engine block, even tried to share ground from these both sources at once - the same ground for LC-1 system and MS of course, I even tried to get the LC1 heater ground from other source - but it doesn't work. I'm not 100% sure if MS gets ground from the source on the photo but I haven't seen any other ground connections going to my MS...
I want to get a separate ground cable directly from the battery and connect the MS ground and LC1 ground to it. hope it will help, Where can I find the MS pnp 94-95 ECU pinout diagram, so I could check which cables to connect to battery ground?
Any comments on my problem? Maybe someone has another idea what distorts my LC1 signal in MS and how could I fix it?