In response to my previous email concerning a buzzing noise from the fuel
pump on my '85 camper, the consensus was that it most likely was a clogged
filter or fuel tank inlet screen.  A little more background:  In February
2011 I replaced all the fuel lines and "upgraded" to the canister type
filter, which is installed on the outlet side of the pump.  In June I
jolted the van when I hit a dip in the road.  The engine died and would not
start.  I had it towed to the local dealership and they said it was the
fuel pump, so they replaced it.  A couple of months ago an intermittent
buzzing sound started but I couldn't trace it to the pump until about three
weeks ago.  Anyway, I bought a new fuel filter and while installing it went
ahead and removed the pump to look at it.  I tapped the pump inlet on a 2X4
and a good amount of grit came out.  I rinsed it out as well as I could.  I
decided that the old box type fuel filter, which is installed on the inlet
side of the pump, is actually better because it prevents grit from getting
into the pump.  I installed a new box type filter and kept the canister
filter, too.  The pump still buzzes.  Since the box type filter is
translucent plastic, I was able to shine a light on it and it looks like
something is moving through it, maybe air.  How can air get into the fuel
line?  If this is a clogged inlet screen, how do I clean it and why does
the van run fine at any speed when it should be starved for fuel?