I got a 03 F150 with a 5.4 v8 and 4R70W. When I give it gas (accel) the a/c goes from the panal to the windsheild defrost area. I also have a problem with the shift on the fly four wheel drive not working all the time. This makes me think it is a vac problems since, both of these use vac to work. How do you track down a vac leak on these damn trucks? It has about 100 vac lines and the dealership aka stealership said there was no vac leak but never put a vac guage on it to test it. SO where do I start?

 

start up by the battery. the a/c and 4x4 vacuum are located there on the firewall. also, there is a vacuum canister behind the battery check the small line going to it. shouldn't be to hard to find.

 

thats what people tell me. I guess I'll start looking, Ernie Haire ford tried finding it today and couldn't find it. They said that it would be two hours to even look but never used a vac guage to figure out if there was even a vac leak.

 

ok man im pretty sure i know what your problem is... open the hood look on the passenger side of the firewall there is a plastic T vacuum line, maybe two of them. My guess is one of them has cracked and theres your problem right there. Let me know