As Joe said, do not use another GM ECM not designed for your year Fiero. I don't mean to be harsh but why do so many Fiero owners do not bother to invest in a multi-meter, fuel pressure gauge, ignition tester and a scanner. My suggestion to you is measure your fuel pressure . It should be about 40-43 PSI .
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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 "