Can't reset codes
 

The MIL light on my ls1 to 66 Buick swap is on. I connected a buddy's cheapo OBDII scanner to it and saw 2 codes. I tried to reset them following the instructions with the scanner but they would not reset. Any idea what the problem could be?

What codes? If they come back on, they either have not been disabled in the computer or you have a problem.

I don't remember the code numbers but it was a problem with the ecm/engine misfire. The codes didn't return, I was not able to reset them. Once I get the fuel pump sorted out, I will scan it again.

OK. I re-scanned the car today. There were 2 P0121 codes which are something to do with the throttle position sensor, 1 P0155 which is oxygen sensor heater circuit malfunction bank 2 sensor 1, 1 P0480 which is cooling fan 1 control circuit malfunction and 2 P1336 codes which are crankshaft position not learned. The P1336 codes are the ones that will not reset. If the computer does not know where the crank is, what problems will it cause in engine operation? Thanks for all the help already provided. This thing would not be running at all without you guys.

You need to de a CASE relearn. Only takes a minute, but you will need a better scanner that has this capability.

Crank learn takes a minute when you finally get it
to go. But I've spent tens of minutes trying to
push the gas pedal just-so, just-when. PITFA.
Fortunately it doesn't need done, except when
you swap the PCM or similarly mess around.

From what I have read of crank re-learns, a conversion will probably not have the needed switches to do it. If I remember correctly, you have to hold the brake pedal down while the re-learn takes place. My 66 Buick does not have the necessary switch on the brake pedal.