Originally Posted by ehsnils
If you have a faulty injector that gives less fuel than the others you may get burnt valves.
But it may also be that the valve in question did fail some stage in production and wasn't caught in quality control.
This is exactly what I think happend to my Legacy. The #4 injector slowly failed over a period of time until it failed completely causing the car to throw a P0304. By then, it was too late. The #4 cylinder had only 45# of compression. I suspect the other exhaust valves are probably not much better. I think this is a serious engineering flaw on Subaru's part as I've had no problem with my WRX wagon. Rather then spend the $1400-2000 to fix this one issue, I decided to trade in the car for a Dodge Ram. Not as much fun, but easier to fix and probably more reliable in the long run.