I have a 1991 Bronco XLT. I dropped the gas tank and replaced the fuel filter. It will run great in the morning. If you try to crank it a couple of hours after running it it will start back firing and die. I don't have bad gas. There is pressure comming from the fuel tank, but when you use the release valve under the hood (the thing that looks like a bicycle tire valve) there is both gas and air. I can't figure where the air is comming in. I can't find a leak in the gas lines. But, I do have a minor exhaust leak. I NEED HELP! Any suggestions?