Today my innovate gauge started to show 21.5 and 7.5 and suddenly it goes to 8.5 and bak to 7.5 , what could cause this?

 

Try doing a recalibration and check you grounds , or maybe the sensor is going bad. I had problems with mine a few years ago , it would give false readings and sometimes an error code after stopping for a short time when I restarted the car. I at first thought it might be heat soak on the sensor , since it only happened after the car set for a while and was hot. But it turned out my battery was going bad and when it sat for a while and soaked up the heat it didn't have enough voltage for the sensor to give a good reading.

 

Check the ground the inovate's are notorious for this.

 

Im gona check that and recalibrate the sensor and lets cee if that will work