Use the supplement manual and go through all the tests on all of the peripheral input sensors to the DFI unit. They tell the DFI just how much fuel to squirt according to engine and atmospheric conditions. Sounds like your engine temp sensor might be bad, though. If it tells the DFI that the engine is always cold, that will richen the mixture. If the air temp sensor is bad, it, too, can mislead the DFI into thinking the air is really cold, requiring more fuel to go with the denser air. If your throttle position sensor is not adjusted perfectly, it will tell the DFI that the engine is trying to run faster than it really is and to add more fuel. And, there are lots of combinations of the inputs to make the DFI dump even more fuel.
Bottom line is, every sensor has to be working correctly for correct fuel mixture.
I'm new to this thread, but to clean my injectors I connected the fuel lines to a small auxilliary can filled with Seafoam, then powered up the fuel pump and used the 12 volt bulb method of driving the injectors from the battery. I ran it like this for over an hour, turning the injectors off and on several times during that hour. Then I let the whole setup sit for a couple of days, and repeated the process. Seafoam may work slowly, but it doesn't harm anything in the system, except the crud you want removed. I removed the whole injector body assembly and watched the spray patterns from each injector. I don't have pics of a correct spray pattern for these, but they were all exactly the same, so,.........
My next step was to soak and clean the bodies in Seafoam, too. The whole assembly looks brand new and orks like new! Seafoam will also not attack the viton shaft seals while cleaning.
Do I like Seafoam? You BET! It works great on fuel systems. It is a bit expensive, but I reuse it and run it through the filter on the above setup as I do the cleaning process. I've done three injector assemblies like this so far. Yep, I do have two sets sitting on the shelf just waiting their turn! (look for me in a future episode of "Hoarders"! I'll be the one sitting in a pile of parts, drinking from a Seafoam can!)