Hi guys. I need a little help here. I got a 86 IROC-Z and I just stabbed in a 350. I got a Hypertech PROM (127062 model) for the 1987 350 TPI. So its right on the money as in my engine conversion. I just started getting a troublecode 51. I went to Autozone and got a Reman Cardone ECM. I though everything was good until on my way to work this morning, I got the same sputtering as before. I pulled over and jumped pins A & B and behold..... Troublecode 51. This leads me to believe that the Hypertech 127062 PROM chip is bad. So my question is, is it ok to temporarily run my 350 engine with a 305 OEM PROM chip? I can easily put back the 305 Knock sensor. I have 22 lb Bosch III injectors installed. Should I be concerned if I run the 305 PROM along with the Bosch Injectors?

 

A PROM swap between a 5.0 and a 5.7 shouldn't be done on a MAF system. In the case you describe the engine will run rich most of the time. If you can (do a quick & easy) change to 19#/hr injectors then it will work.

Although be careful of higher RPM/load as they won't be enough to completely fuel the engine.

As for the bad PROM, it may also be the MEMCAL or adapter that is bad. Since this needed to be swapped over to the new/used ECM.

Moving to the DFI & ECM board as it isn't related to DIY PROM tuning.

RBob.