Now I have time to explain this.
I was hurry to catch my train to my uni. that day , and I have finished all in fact ,but sadly , I "locked" the car and the game can't load it.
I don't know what the matter is , soon I realized that the "lock" I tested on my renault is not a locked car in fact , I use "Benetton" as the slot name for my Renault that day and when I first time and laters tested the damage model , I directly instered the .gp4 file car_renault_1_lod0.gp4 into the cars.wad...
I didn't get so much chance here to be online ,but I may contact another expert of making cars(or extractly conver cars) to finish the work , and release them at a correct time.
That's all.