sounds like someone is hitting the dash from underneath at 70 mph--van runs good w/318 motor--any thoughts?

 

Something loose?

 

Bad motor mount, and the engine is bouncing around?

 

A flapper/door inside the HVAC assembly perhaps?

 

thought this was a common mishap with these vans and my 89 b 250 with 318 does it also

thanks for the replies....it's scary--but ran all the way to Sturgis and back in august

ran to Frankfort and back yesterday

hard to get someone here to even look at it