I'm working on a 1998 F-150 4.6l with a hydro locked cylinder. I pulled all the plugs and had water in #1. Before I just assume BHG, Are there any intake manifold issues with these motors where a failed gasket can allow water into the cylinder? Are there any other issues that I would want to know about? I'm unfamiliar with these engines specifically but have been a mechanic for quite some time so any info would be great. I'm diving into the Upper intake tonight to further diagnosis the problem.
Thanks

 

There are incidents where broken manifold studs being drilled out too deeply and causing this same condition. Have you or will you do an individual compression or leak down test before tearing it all apart?

 

I Haven't yet. Planning on it today.

 

Those tests will help determine a BHG naturally--you already know that though.

If there's water in a cylinder and no other work has been done before you began it would seem to be a BHG is the likely culprit.