i have a 91 mustang lx 5.0
302 bored over 30
40 gt heads
tow cam
stock block
bigger throtle body

just added 42lb injectors, 255 walbro fuel pump, 90mm maf, and on3 sinlge 76mm turbo kit
tried to have it tuned was told car would not hold a tune and that i need
to change the ecm and wiring harness if so what set up do i need to go with

 

find a different tuner......guy is an idiot, who probably tunes ricer obd2 crap, you need a sct chip that plugs into the j3 port and can have multiple tunes written to it. find someone who knows mustang tuning in your area for eec iv equipped mustangs