Mechanic read codes with generic reader--#300 and 301, which says #1 cylinder is shorting, which is obvious and unrelated, because the plugs were fouled. Volvo Houston said no, it wasn't the fuel rail pressure sensor (which fluctuated from 396 to 9 kpa, whatever that means), and so had to be further up the line, i.e. the fuel pump. Failing fuel pump would cause rich mixture by over pressurizing the system causing the injectors to insert too much fuel? Doesn't sound logical to me. Volvo Corvallis Master Mechanic said no, not fuel rail pressure sensor, not O2 sensor, nor vacuum line break. He was at a loss. I walked out no wiser than when I walked in. Are those fuel pressure parameters, 396 to 9 kpa within spec limits? Would a failing fuel pump cause this much variation, or is this normal from say idle to race? Nor would a failing fuel pump over pressurize the system, would it? I don't understand why this so called sophisticated OBD-2 diagnostic system only kicks codes as an after effect (shorting #1 cylinder) and not what's causing the initial too rich mixture, but codes #300 and 301 were the only ones the reader showed. Dick