My Firebird (91, v6, 700r4) has a long history of oddball problems. Now recently ecm issues. Every now and then, VATS acts up and will not let the engine crank (throws code 46). Half the time when this happens, it throws no codes. The last time this happened, finally threw me codes 46 and 47. It did not retain the codes for long. I flashed them right away. An hour later when my buddy came over, they were gone. I did not unhook the battery or clear them. The next day I started the car up, ran rough and misfired every now and then. It was rougher in the drive gears than in neutral or park. I checked the timing, it was advanced to hell and jumped. ECM threw no codes for this. Shut the car down and it was fine 10 minutes later. There is not much information on code 47. All the information I found on it said it usually indicates a loss of bcm data in the memcal, hence no long term memory. Sometimes it does not remember it's idle speed either.

Could it be possible that all these problems could be traced back to that?

 

Code 46 is VATs, there is no code 47 for that ECM. It sounds like there is a power feed issue to the ECM. Check the battery cables along with the main ECM power feed. The power feed is along the passenger fender under the hood. There is an inline fuse with that.

IIRC it pulls power from the terminal block on the passenger side of the radiator support. There are also some fusable links there. Check those along with the ones on teh starter.

If all looks good it may be that the ECM is bad. The VATs acting up may be nothing more then a dirty key or bad contacts in the igniton lock cylinder.

RBob.