Technical Service Bulletins can be found by doing a search on the net. I haven't found the right place to view all Ford
TSBs. A close friend is a warranty claims adjuster and is an encyclopedia of knowledge and can get this info for me.

I had my 99 Expl XLS cleaned and I continue to use Fuel Injector cleaner every other fill up - and it helps keep the knocks down.

Tango.