I am in the process of trying to get rid of my lean codes on my 1998 ranger 4.0L. With the help of some threads on this forum, I started tearing off the upper and lower intakes and gaskets. While I had the lower off, I removed the fuel rail and the injectors. After watching a couple of videos on YouTube on cleaning injectors, I took a stab at it. I used a syringe with fuel injector cleaner hooked to a short piece of tubing and then to the injector. I also used a two wires with alligator clips and hooked them from the injector to a battery with a switch. I thought all 6 seemed to flow pretty well and I took a short video of one of them spraying. I was going to replace the o-rings on all the injectors but was wondering if I should do anything else with them before reassembly?

 

I have not heard of fuel injector problems on any ford product since introduction ~1985, when multiple injectors began to be installed on the Lima. I would just put it back together. I cannot see any pics, but one thing older injectors had at the nozzle end were 'hats' made of plastic that seemed to disintegrate when the injector was removed from the fuel rail. If you have that problem, the hats can be purchased separate from the injector, but you'll have to search for them.
tom
added: Do not leave the injectors 'powered' for a long time. They are designed, I think, for 'pulsed' operation and may get hot if left connected to power.