Steve91Z28 L98

I recently bought an Auto Xray XP240 scanner. I calibrated it for my car which is a '91 Z28 with the L98 motor (originally). I entered the 8th digit as "8" and then it asked for the 4th digit which is an "F". After that it goes back and says 5.0 Liter: Yes/No. I check "NO". First off, why would it ask me this if I already put "8" as the 8th digit?? Anyways, I go to scan and it gives me "SCAN ERROR" I tried numerous times configuring it and kept getting the same result. Just for kicks I answered "Yes" to the question of if it was a 5.0 liter. I went to scan and it worked!!! Why would it be doing this? I'm not sure if I'm getting proper readings this way. Thanks in advance for your help.