Is the MSD distributor locked out? You have to pull the distributor apart to do this. Sorry about jumping on this late... Another thing you can do to test the waters is tell the EFI to leave the timing at zero, do not connect the EFI to the MSD input (white wire usually) and let the MSD take care of the timing. Long run you do not want to do that but it would be a test. Put a timing light on it and see if the timing moves. If it does the MSD is moving it somehow.