I just filled my 1999 3.8l mustang up with gas, and now it won't start.

I know this sounds unlikely, but throttle body cars flood, just like a carbed car did. the next time it happens, push the gas pedel down to the floor, and crank the car until it starts. when it starts, don't be alarmed by the smoke, that's just the excess fuel being burned. flooring the pedel will allow more air to the cylinders, and finally the mixer will even out and the motor will start. another thing to check, is to make sure the gas cap is on and tight, let it click a few times to be sure, since it happen after you got gas, that could be whats wrong....hope this helps

Js I want to thank you for your answer, I did change this and it did start again. RS, i did have to push the gas pedal to the floor, and yes a lot of white smoke did come out. But the car is running fine now, and I want to thank you ALL for your response. This was very helpful.....OPUS

That's what nice about this website, you never know who you might help. And there's no thanks needed, I feel good by the help I give to others,and the help I get from other people. Great things happen to you, when you give !!! Hope this helps....

lol lol. what goes around, comes back around!!!!!