I have an '07 f-150 with a 4.6L. I live in Denver and when its cold, it makes strange noises upon start-up. It also has a "spark knock" the dealer has had it 2 times for maitanence and I have told them about the problems, they say that they can't find anything. has anyone else had this problem and if you have, what was the problem??? any help would be great.

 

What noise does it make at start-up and where is it coming from?

When does it do the spark knock?