My 94 4.0 is throwing a burnt smell into the cab upon a good acceleration like when entering fwy. Exhaust pipes muffler and cat are fairly new. Where would i begin to diagnose.

 

Check the rubber seal at the base of the windshield on the cowl panel. It's supposed to seal out engine compartment fumes. Also make sure all rubber grommets in the firewall are in place, and there are no open holes. Do you have a full length exhaust system? A short tail pipe or dump, or a leaking/rusty one w/holes in it could allow exhaust fumes into the passenger compartment.

 

That was it. Thanks no more smell. Well at least inside the cab.

 

That seal helps prevent fumes from being sucked into the HVAC air intake at the cowl panel.

 

In your experience is that seal prone to falling off the track or should I look at replacing?

 

Mine was always falling off. I glued it on. I pulled off one side at a time, stopping at the center to keep it in the right position. I used some weatherstrip adhesive on the metal lip and reinstalled it. Never came off again.
Mine was in great shape though, not tore, or dry rotted at all. If yours isn't, you can look at the JY and probably find one in great shape.