Okay so here is the deal guys, I have a 1993 ford f150 with the 4.9 straight six. I have been driving myself crazy trying to figure this exhaust leak that i have been hearing for a long time now. I have yet to find a leak in my exhaust but i have been reading stuff on the internet and im thinking i may have a leak in the secondary air injection. I hear this ticking type noise but only only when under acceleration, like when i am building rpm's or going up a hill, i cannot really notice it my cruising at a steady rpm. I have yet to get under the truck and look at this air injection, but i do know that the tube that runs down to the cat has rusted off and is not connected to the cat anymore. If i find a crack or broken tube up near the motor, what is my best bet? To replace the whole thing or is there a way of plugging it? Any help is appreciated, this noise is driving my crazy!

 

"...but i do know that the tube that runs down to the cat has rusted off and is not connected to the cat anymore."

Replace the tube and go from there. And it could be that the Cats are overdue for replacing too.