I'm surprised that nobody jumped in to tell you what the difference is between the injectors. The 19lb and 21lb rating is the fuel in pounds delivered by the injector in 1 hour at WOT. Obviously, the 21lb delivers more fuel. I would not expect any issues with putting the 21lb in the truck for normal operation but fuel mileage may drop and you might have issues with it at full throttle. Some have issues, others don't. So it's a case of you'll have to try it and see. If you don't have issues or maybe minor high rpm issues, a tuner can be a big help for some.

 

Call PHP and ask they could tell you what needs done...just my opinion...

 

2lbs is 907 grams

 

The PCM should be able to trim back the fuel mixture enough by shortening pulse width at low speeds... but maybe not. Don't know the specifics of that particular combination. WOT would be another possible problem (not in closed loop at that time) but since Ford tends to calibrate a little lean for power, you might be alright (possible loss of power). Might get really messy if you used a programmer later. Why are you so insistent on using these... you get some freebees?

 

My question as well as there is nothing to be gained but inefficient fuel control.