I have a 89 GMC S15/T15 Jimmy 4x4 4.3L 2dr truck. About a year ago the truck started to give off a horrable smell only when reaching 50+ mph. It smells like burning plastic that is unbearable and gives me an instant headache. Due to this, I have not been able to drive over 50mph. I also noticed that as the smell begins, a grey/whiteish smoke begins rolling up from the floorboard in the back. Everybody seems to believe it is exhaust fumes, but this smells like somebody is melting plastic or glue. I was thinking it could be the catalytic converter. Has anyone else experienced this? Does anyone have any idea of what the fix could be? Thanks

 

Well, start by checking over all things hot on your truck. See if something has lodged itself up under the truck and is melting against the exhaust. Also run through the front and rear diff lube levels just to make sure that they are filled properly.