Ok I will start by giving you some background on my set up. I TPI set up that uses a 730 ECM. I am using a Street & Performance stand alone harness that is made to use with the 730 ECM. The whole car is fresh and has no miles on it(its a 57 Nomad). Whenever I fire it up the check engine light stays on all of the time and it is either in fail safe mode or limp mode. It will give no codes thru the check engine light and willl give no data on a scan tool either. I know the ECM is good because I swapped it out with a known good one and I have had a reputable chip burner check the chip and he said he could no problems with it. SO I guess my question is what can casue the ECM to go into fail safe, or limp mode. Thanks for the help. Steve

Steve, if you're getting nothing through the ALDL terminal to the scan tool then something's out of whack. That's an indication of a problem right there. Given that the ECM has been replaced with no change I'm gonna guess that the harness is screwed up (or wrong for the application).

I'd get in touch with the wiring harness manufacturer and go though it with them with a fine tooth comb.