I have a 1990 F250 truck with a 5.8L engine and was told by a mechanic that this truck does not do well with the AC Delco spark plugs. What would you suggest or are this plug okay to use?

 

I felt Ford products those years performed best with Motorcraft spark plugs

 

Been there, done that, heard the same thing from other mechanics. They created issues when I tried ACs in my 1983 Mid-Sized LTD 3.8L and 1988 Ranger 2.9L. Motorcrafts cured the 3.8's issue and the 2.9L liked regular Bosh Platimums.