First off what engine are you using with that computer that you intend to use. Is this this for the Fiero 2.8L engine or an engine swap. If this ECM is to control a 3100 Buick engine then you will need the original harness rewire it accordingly and combine it into the existing Fiero wiring harness, Then you will need to reprogram the ECM by changing the chip program by re-writing the code to suit the engine and your Fiero. You will need an editing program to do this and a programmer.
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "