Air intack and discharge

[tpcboston]

I have an oil burner that is vented through the house. On the outside I have and air intake (looks like a drier vent) and an air discharge unit ( an 8inch square vent). They are only 6 inches apart. I have been smelling oil in the house and have had the unit checked. The only thin I can think of is that as the discharge unit is pushing out the old air from the unit the intake is taking it right back into the unit.
Is there supposed to be a distance between these units.