I went through heck with erratic and high RPM and fuel pressure indications. I dealt with the RPM issues for over two years and the fuel pressure about 6 months. I have a Vision Micro Systems VM1000C. It uses a Hall effect sender on the magneto for the tach and a VDO sender for fp (fuel pressure).
These problems were very frustrating because I was doing all of the “right” things to trouble shoot and as soon as I thought I fixed it, the problems surfaced again. I checked connections and did continuity checks multiple timeis. I sprayed contact cleaner. I pulled on pins and wires. I replaced connectors. I replaced the Hall effect on the magneto twice. And fortunately, a friend of mine had another VM1000C display that I swapped out. The problem persisted. With only 3 basic components (the sender, the display, and the wiring), I had replaced everything except for the wires themselves. I doubted replacing the wiring would fix it because of the many continuity checks I had done. Finally, I replaced the three wire harness to include the pins on the display end, the Molex connector on the sender end, and the wires in between. I’m happy to report that the problem with my tach is finally fixed. As soon I was convinced that my tach was fixed, I replaced the wiring for the fuel pressure. And voilà, my fuel pressure was fixed. I wish I would have known it was that easy. I had been through three VDO senders and various connectors. The frustrating part was that I had done many many continuity checks while moving and jiggling wires.
Good luck and let us know how it works out.