Could be the plugs, you probably would have been better off with some NGKs. Did you replace the wires too? You might have damaged the wire that might have set off the light. Or could be an O2 sensor or intake gasket. But more than likely the issue is the plugs.

Dan

92 Rodeo, 3.1 TB crank, custom bumpstop spacers, DOR shackles, Flipped ball joints, D44 Rear, 4.56s and new magnaflow cat and dynomax ultraflow muffler Since been replaced by a 2 door Explorer on 31's shackles, cranked torsion bars and full exhaust