One thing that comes to mind is that the car's ECTs, which must rise above some temp before it will let it go into closed loop. Another would be the signal from the O2 sensors, i.e. the "HEGO" voltage. If they're out of range, the computer would recognize this and remain in open loop. You'd probably have a CEL if this were the case, though.
Take a look at the other numbers in the data log, TPS, MAF, IAC, etc... Make sure everything's within reasonable ranges.