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the last 2 3400 swaps I did used 3.1 injectors on stock obd1 ecm's and they both run fine. the bigger injectors will make more power with a tune, but the first thing I would do is start with a better fuel pump. when I first put the 3100 in my old 84 cavalier I went to the track then swapped to a Camaro LT1 fuel pump and went back the next weekend with no other changes an dropped almost 4 tenths off my ET. if I was doing a basic (stock) 3400 swap on a obd1 car I would use 96-99 3400 or 3100 injectors with matching fuel rail (2000+ injectors will not work on stock ecm) or 2.8/3.1 injectors with a 2000+ 3400 fuel rail that has the higer pressure regulator. But if I was mooding a 3400 and dropping it in I would use injectors sized for the fuel requirements of the engine and a full tune.