Ya maybe i'm not meant for car mods but I can sure have a go at sound mods! Hmm only if Alex finally got around to teaching me... (said he was gonna about a month ago and never heard from him ever again.)
But the biggest error you made (and this is the one that will probably sting a bit)
You dont really seem to listen to people that well. You ask advice, you get given it, but then its like you just pick and choose little bits of that and run with it. Then hit a brick wall and have to ask pretty much the same thing again and again.
If you don't take on board the whole thing, you will always end up making mistakes, often the same ones several times.
Sorry if thats a little harsh, but if nobody tells you, you will never know. And i have experienced this with you personally and with other users on several occasions. so it is something that has popped up a few times.
(im really not trying to kick you while you are down, it genuinely is meant as honest advice)
smooth. yeah you dont seem to be having the best of luck anywhere with 3d model related stuff.
You SOME HOW managed to merge an entire car into one solid mesh, apparently without actually merging anything or saving anything You have managed to over write original game files with the wrong stuff. You seem to have issues with most aspects of getting the model ready. So id say maybe its time to call it a day on 3d modding (for now)
Try moving onto doing a different aspect of modding, like making skins, we really dont get a lot of new skins made these days. Or sound mods, or even texture packs, like those winter/spring mods.. Thats nothing more than unpacking the textures for say "trees" and creating newer, better tree textures, and repacking it.. No different from creating a new license plate..