I have searched all the forums and maybe I just did not use the right keywords or phrase but I could not find an anwser to my question. And sorry if this is not posted to the right spot. Also sorry for the length just trying to provide enough information. I have another good technical question for the 5.0 Mustang Forum. First a little background on the situation, I picked up a four cylinder 89 Notch for 600.00 minus the motor and trans and performed a V8 swap (AER manufacturing 306 long block, FRPP E-303 cam, FRPP 1.6 rockers, FRPP 24 lb injectors, 70 mm TB, FRPP Tubular intake, BBK shorty headers, H-pipe, MSD billet distributor, MSD A6L, MSD coil) replaced the computer with an A9L, complete engine wiring harness, fuel injector harness, headlight wiring harness with a 3G alternator upgrade, all were from an 89. None of the harnesses have any splices or repairs made to them other than where I adapted the alternator upgrade, all sensors, switches were installed new. And now the Question, I get a check engine light coming on after driving it 10-20 minutes, if you shut the car off and start it right back up it does not come back on until after 10-20 minutes again and the local auto shop is unable to pull any codes because they cannot communicate with the computer. I switched the computer out from 89 notch with my 89 convertible and they can read it there fine. The car runs fine until the check engine light comes on then it runs sluggish. I drove the car for about 300-400 miles before check engine light problem started. Any help on this is greatly appreciated.