Let me guess. you touched the suspension? or the chassis? Dont modify the jbeam of the suspension unless you know what you are doing. as for the chassis try to keep the mounts as untouched as possible, if they end up interfering with other parts use {"selfCollision":false}
Actually ninja'd by me, 12 or so hours ago OT: Coming along fairly well, this is the first kind of blueprints modelling that i've done.
You could try adding a plate holder? (i dont know if thats the name, im talking about the thing that goes over the license plate and acts as a handle for the trunk door too.) (It would also make the trunk door a bit less bland. And add realism too)
According to all known laws of aviation, there is no way a Pigeon should be able to fly. Its wings are too small to get its fat little body off the ground. The Pigeon, of course, flies anyway because Pigeons don't care what humans think is impossible.