P0306 1998 Ford F150 -

Question

What is most likley the problem. I've changed spark plug on #6 cyclender and wire.

Answer 1

Hi there,

With the engine running, try spraying some carb cleaner along the intake manifold to check for vacuum leaks. If the engine runs smoother or if the idle speed increases, then you have a leak on the intake. If that doesn't resolve the issue, then the next step would be to try swapping the fuel injectors to see if the misfire code moves with it. If it does, then you know the injector is the issue.