This past weekend, I had what I presume is failure of the engine-driven fuel pump on my RV with IO-320 (engine was factory-new, now with about 400 hours). I was about 350 miles into a 500 mile flight. At the start of the flight, the engine had started and run fine, and all engine displays were in the green for the entire flight. Stopped for fuel and lunch, afterward the hot start went OK but running a little rough. I noted on the EFIS engine display that fuel pressure was solidly in the red at about 4-6 psi...not RPM-dependant. That was new. I taxied out planning to see what it did on runup and the engine died on taxi. I got it started...the pressure was still low... I hit the boost pump and it jumped into the green. Boost pump off...engine died. I found a mechanic at a nearby airport, that had a fuel pump on the bench from an O-320 he was rebuilding. He switched it out...the engine ran smoother but fuel pressure was still in the red at 7 psi. Am I correct that the IO-320's have a higher pressure mechanical pump than the non-FI version of that engine? The guy was nice enough to store the plane inside, ordered a fuel pump (same model as the one that failed - the higher pressure version) and will put it in on on Wednesday. We're presuming that the engine-driven pump died and the pump he tried replacing couldn't manage sufficient fuel pressure for a fuel-injected engine. Opinions....? I'm under the impression that engine-driven fuel pump failures are kind of rare on these Lycomings but this plane had been hangared pretty much unflown for about a year. The fuel pressure gauge had been green the entire flight, until it wasn't after re-fueling and the engine died. Flipping on the boost pump put it back in the green immediately. Seems odd, but I can't think of any other fuel issue that would act that way except fuel pump failure. Other thoughts? Something I'm missing?