This sounds more like a hardware problem. Try using a different type of CD or try the program in Nero called Nero Burning ROM. In the guide there is a link at the bottom to another guide for Nero 6 (Nero Burning ROM). It doesn't look quite the same but it's still very similar. Choose a very low speed for burning like 4X. That should help with players that aren't really compatible for the burned disks. Also try buying some more expensive disks.

Have you tried the 4 disks, that couldn't be read in on car, in any other CD Players that support CD-R?