Hi I have an 98 SC with the 4.6. My check engine light comes on at freeway speeds of 70 plus. If I disconnect the battery it stays off untill I get on the freeway. I doesn't always come on everytime I go 70. So I went to Auto zone and they checked the codes. The code 0455 came up and said emmision control leak (large). All they told me was look for vacuum leaks.Does anyone hava suggestion where to look? I started just looking at hoses, then I thought I would post the question here.I appreciate any help. Thanks Bob

 

Could be caused by a bad gas cap seal.

 

Thanks for the advice. I looked and my filler neck and it has a small crack. I filled it with gas tank repair putty. So far so good no light. Thanks again for your help.Bob