Comment by jabart
This happened to me! Friend had a similar car and at night they went to mine and the door unlocked but the car wouldn't start. The door only had a few pins it checked while the ignition used every pin. We compared our keys and sure enough one part of it was the same.
OBS Ford F-150s do this and it's not common knowledge even among enthusiasts. The back 4 pins work the door, the front 6 or so pins work the ignition. A common problem is that the ignition barrel keyswitch dies and you have to replace it, but then you have separate keys for the door and ignition. I took the new ignition key to a locksmith and had him copy the 4 back pins from the factory key, and I was back to a single key!