I am in desperate need of help before I have to take my truck to a shop. I have a 2001 F-150 4.6L, I have researched this and cannot find anything on my problem. When the temperature is cool outside my truck runs fine even when the motor warms up, however when it is hot outside the truck runs real sluggish and misses. It misses the worst between 45 and 50 mph but runs fine at faster speeds. Has anybody else had a similar problem or any advise for me?

 

Run the codes first and see what comes up. Heat is an engines worst enemy. It could be almost anything. Check and see what the computer says and then we can go from there. It could be as littles as a hose being lose or cracked to who knows what else. Do the codes first and tell us. We'll be able to better judge and NOT guess a hundred different things.

 

A miss at 45-50 is often times caused by plugs/cops. A scanner will be able to show which cylinder is missing.

Not sure about the hot/cold problem.

 

The only code that comes up is for the gas cap that I have already replaced. There is no misfire codes, I go about once a week and have the codes pulled at auto zone.

 

A failing cop will not always misfire enough to throw a code. Any decent shop will have a scanner that can monitor the systems in real-time to see if there are any issues.