Hi Mark,

Unless the pump or another device has a bladder or diaphram to hold pressure when the pump is off, the line pressure should return to zero. Maybe the regulator performs this function also? Any rubber lines that expand at all under pressure would account for a very small amount of pressure also.

I think with the engine (and pump) off, there wouldn't be any pressure in the fuel rail. Fuel yes, but not under pressure. When you turn the key, the pump starts immediately to pressurize the system before the engine starts.

I've noticed the schrader valve on the end of the fuel rail and suppose it's for testing pressure or draining the rail.

A leaking injector would show itself in other ways like poor running, hard starting, fouled plug and if bad enough, gas in the crankcase, poor lubrication of the cylinder wall, diluted oil and maybe a bent rod. An oil analysis would tell you if you have raw gas in the sump.
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Erwin in Memphis, '95 855t