i have a 90 f150 with the 5.0. the previous owner apparently swapped in a 5.0 from a 94. the fumes are horrible. its to the point you cant turn the air or heat on because it pulls the fumes in even worse. i looked under the hood and noticed a leak under the top of the intake manifold right around the top of the valve cover. i know the exhaust manifold gaskets are good just replaced them. could a bad intake mani gasket cause fumes to come into the cab also?

 

Its possible. If there is an exhaust scent under the hood it can find its way inside through the HVAC no problem.

 

yea its gettin worse by the day. and dread turning the heat on. i noticed the leak yesterday. its on the pass side right under the top half of the intake mani. they sell just the intake plenum gasket or the entire intake mani gasket kit. i guess im better off buying the full gasket kit for it. damn truck is nothing but a money pit

 

They should be available. Check out LMC Truck or Summit Racing and see. Those 90s F150s aren't real reliable in their older age.