Did you replace your intake manifold your self? Did you use the dorman manifold. It's a possibility that who ever replaced it could have installed it wrong or torqued the intake bolts around cylinder 4 incorrectly. It's also a possibility, if you used the dorman manifold, that the cylinder 4 o ring is missing or something is preventing it from sealing. Test for a bad head gasket, and if that test comes up negative then I would double check your intake manifold

 

Do u know exactly what I should get to test it?

 

To test the manifold or to test the head gasket? Just go not auto zone and ask for a head gasket test kit, they should know what it is. The only sure fire way to test if there is a missing O ring or bad gasket on the intake manifold is to take it off and check. You could spay down the suspect area with carb cleaner while the engine is running, if your ideal changes then there is a leak there.

Do yo know if you used the Dorman intake manifold to replace your stock one or did you use another ford one?

 

I will ask my dad tonight, he's the one that bought it.

 

Is the test a compression test???

 

No it test for gases in the coolant