Ford Exhaust System :: Exhaust Manifold Leaking / Louder Than Normal Knock When Accelerating

Leaking exhaust manifold? The truck has a much louder than normal "knock" when accelerating. At first I thought and had some bad fuel in the tank. I eliminated that with a full take of good fuel and some STP but the "knocking" continued. Then I thought that perhaps it wasn't firing on all cylinders but it felt like it had full power. I took it to my mechanic and he said it as a exhaust manifold leak. He said that he has never replaced the exhaust manifold but that it was a "nightmare" and expensive. He also said that it's not a safety issue but on the long run the leak would cause the truck not to pass its emission test. He said the problem was with rusted bolts that would be difficult to remove.