Kevin Stallard asks:
> Actually the question really is, why does the IO-550
> require an electric fuel pump (besides priming/starting)?
>
> Why is there both a low boost and high boost pump?   Is this only
> for backup, or are there more sinister aspects of fuel delivery
> in the IO-550 at play here?  In talking with a friend of mine,
> he mentions that the Lycoming io360 only has a low pressure fuel pump.

Search the web archives for "IO-550 fuel injection system"
or "Boost pump use" or "Summary - when to turn on the fuel boost pump".
There was considerable discussion starting 1 Feb 2007 and going
for about a week. Of particular interest is an article from Gary Casey on
how the Continental fuel injection system meters (or fails to meter)
the fuel flow.
http://lancaironline.net:81/lists/lml/Message/39747.html

The thread is summarized here:
http://lancaironline.net:81/lists/lml/Message/39857.html