After driving a few miles, the oil pressure gauge on my 2003 Bonneville with 203,000 miles will start bouncing between 70 to 120 psi, the car will start missing out and eventually stall as if not getting fuel. The sensor/sending unit has been replaced twice but the problem re-occurs. 2 mechanics are stumped. Any ideas?
Just a really wild guess, could your ignition wire be shorting to whatever feeds the oil pressure gauge?
The engine in this car should not have oil pressure that high. Those engine will be happy at 50 psi at high revs.
Have a trusted mechanical gauge attached so you can see if that 120 psi is real. If it is, the oil pressure relief has jammed and it is loading the oil pump so heavily it might be stalling the engine. If it is not real, follow @oldtimer-11 's guess to an electrical problem.