Certified flight instructor with student pilot flying a Mooney M20C reported that they had to reject the takeoff due to low RPMs. On the second attempt they rejected the takeoff due to low fuel pressure.

Narrative

During a routine training flight; myself and my student went to advance the throttle for takeoff. During the advancement; the propeller did not accelerate passed 1900 RPM which is insufficient RPM for takeoff for the Mooney M20C.I called to reject the takeoff and my student pulled the power back and applied brakes. We exited the runway at the next taxiway.We taxied to the run up area to do some trouble shooting. During the run-up; no abnormal indications were experienced. Full power was applied to the aircraft and a full power run up was completed. With no abnormal indications; we elected to try the takeoff again.We eventually got clearance for takeoff and applied full power. Halfway through the takeoff; the fuel pressure gauge read .3 PSI (in the red)(Normal fuel pressure indications are 5+ PSI). I once again elected to reject the takeoff because I assessed that the aircraft was not safe for flight. We taxied clear of the runway and decided to stop flying for the day without further incident.At the time of the occurrence; the Annual/100hr inspection were in compliance. Additionally; all airworthiness directives were also complied with.