Cylinder 4 misfire along with a big incomplete cat convertor weld and exhaust manifold cracked?

Hello, it could be possible as this would be considered a vacuum leak as it is before the O2 sensor and will throw off the fuel trims. To test exhaust leaks I like to take my shop vac and secure it to the exhaust pipe and turn it to "blow" and spray areas with soapy water. Otherwise, the manifold will be too hot to test for a leak.

In any case, here are the instructions for removing this manifold:

1. Raise and suitably support the vehicle.
2. Remove the exhaust manifold pipe nuts. (Image 1)
3. Lower the vehicle.
4. Remove the spark plugs.
5. Remove the exhaust manifold bolts, manifold, and gasket. (Image 2)
6. Discard the gasket.
7. Remove the heat shield bolts (1), and shield (2) from the exhaust manifold (1), if necessary. (Image 3)
8. Clean and inspect the exhaust manifold.

Hope this helps,
William