Does it have dual tanks?
If so there is a second filter inside the fuel tank selector valve / reservoir.
It's located down on the frame rail behind the high pressure pump.
You will have to remove the skid plate to get at it. Unscrew the base of the reservoir to replace the filter.
Ford states that the filter is lifetime part but I had to replace it 2x before finally replacing the whole valve with an electric switch valve. I also put a generic filter in each fuel line. My real problem is that a bad sender pump in the rear tank was sending junk through the lines - replaced all that too.
In my case I could not go over 50 mph at which point it would start sputtering and act like it was running out of fuel. At the same time the main fuel pump would whine. Below 50 it would be fine.
I thought 86 was the 1st year of the EFI engines?