[Kazimodo]

winter fuel this time of year has already started to lower the efficiency of MPG,
( if you are in Florida ,,,,, NO on the winter fuel theory...).
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possibility of sound and smell , turbo up pipe , can develop a crack ,
leak and smell goes up the firewall right where the cabin air is drawn from .
use a 4 feet long piece of old garden hose , stick one end near your ear and send the other end
down behind engine , if your truck is up on a lift , from passenger side front wheel housing
you should see the area you want to probe , if the exhaust leak gets higher in the hose while
engine is running and hose moves around the turbo up pipe you will have confirmation .
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images , one is of cracked turbo up pipe , other complete turbo up pipe..

 

[Kazimodo]

Kst8er , in an other thread about the flange bolts coming apart , another member reported
that the heat , from exhaust leak created by broken bolts , melted
the wiring to the DEF injector . could explain you dash message .

in here : Exhaust Flex Pipe to SCR Flange studs snapped