What is code 51 I am just now noticing it. I thought all I had was the o2 sensor so now I have 12, 21, and 51..

ANyone know what 51?

welcome to the club. If you happen to get a datalogger and use it to diagnose, you'll get P0171 whish is cel 51. Lean fuel mixture. I have it, but I'm not sure what's causing it. A few other guys on here have it too. I've tried fuel injector cleaner. But still have same CEL. If you find out what the problem is and have a solution, or anyone else for that matter, please share it. I need to get rid of it so I can start boosting again. My A/F ratio is working correctly, I think, and it shows real rich at WOT or under load.

Well not knowing what you guys are using as MAP sensor voltage clamp, turn your igniton key on, but dont start the car. Use a voltmeter and measure accross the map sensor to see what the voltage is at. It should be at 4.5 volts. If not, then you either have a MAP problem, or our voltage clamp is at fault. I just found out about my HRC FCD is bad, causing me to run way too lean at 7 psi, even with over 100 psi of fuel pressure..check it out to make sure, cant hurt..
It could also be the o2 sensor, it may trip more than one code number..

Well when my voltage clamp was messing up I was getting code 14.
BUT I got rid of that thing and now I have the missing link, check valve for the map sensor, and the wires for the MAP are put back to stock...unless one of the wires came loose which I doubt since I soldered them back together.
How do i check the voltage?
Turn the key on and then where do I stick those two points of the tester?

its all probably caused by the o2 sensor, its reading incorrectly hence throwing off the fuel mixture.

Replace that first reset the battery and see if it comes back