Originally Posted by jtaylor1920
I'd call your local Ford dealer and talk to the warranty manager to be sure. I know on my Ford diesel they will void my warranty if I use a tuner or modify the exhaust system, but I'm not sure about the gas motors.
There is a federal law called Magnuson-Moss act that answers this question fully and completely.
It state (in effect, and amongst other things) that unless the aftermarket part can be proved to be the cause of failure, then your warranty cannot be voided. In other words if you add a tuner to a diesel, and melt the crowns off the pistons with high exhaust gas temps, then you can fully expect Ford to say "tough cookies". But if you add a free-flowing exhaust, and your torque converter coughs up blood, its a pretty sure bet that the Ford warranty will apply. Which is to say Ford won't try
to deny your claim.