Exhaugst smell through air ducts.

[spacedog]

I am getting exhaust in the cab throught the vents when in 4 x 4. Put it back in 2 wheel and it goes away. Any Ideas where to look for the cause? The exhaust was upgraded to an MBRP 4" turbo back about a year ago and everything on the exhaust seems to be tight. Also I am mechanically challenged the majority of the time but I try. Thanks

2002 7.3 PSD

[nunly81]

Hmmmmm, that sounds fishy, the only thing I can think of that would do it in 4x4 only would have to be a vacuum hose. But it just uses that to engage the 4x4.