Help with EI OPT-1 Oil Temp and Pressure indication

[maximo64]

Hello: I have an RV-6A with many EI instruments installed since new (aprox year 2000). No problems until now. They are very good instruments. My problem however started some months ago with in flight sudden changes of temp and pressure indication, sometimes going to the low zone and the Red Led turning on.
I discovered later that the cause was when I was transmitting (pushing the PTT) the OPT-1 showed wrong values.
Did anybody had the same problem ?
What do you thing can be the cause of it ?
I already checked ground connection on the transducer and the instrument.

Thanks !
Maximo Lema.
RV-6A
Buenos Aires, Argentina