Q. I have a problem with diesel fumes coming into my cab of my 2006 king ranch 350 ford diesel truck it seems to be coming in through the heating system - Simon

A. Morning Simon,

I would take a good look at the exhaust up pipes between the exhaust manifolds and the turbo.  There are a couple of expansion joints that crack on a regular basis.  They are directly behind your dash and when blowing on the firewall can lead to fumes in the cab.  It is usually pretty easy to spot where the break is because it will be covered with soot all around it.