Don't bother with the cut off switch, you already know its getting fuel. And Failed o rings wouldn't cause this.
The sequence is different for different years. I've heard some that just buzz solid, and some that buzz all of them, then buzz each one in sequence of cylinder number, then buzz solid again. But if it doesn't sound right, then it's probably not. How many years have you been listening to it? You would know if it sounded different.
You need to figure out if it's commanding fuel or not. All other tests are pointless or redundant right now. Except a shot of supplemental fuel, that should be done also.
What is causing his hissing and spraying from the secondary filter? That clearly is not typical and is not a fuel command issue (or lack thereof).
Also, if he has FICM
sync, it should be commanding fuel shouldn't it? ... especially since he still had these problems with a known good FICM
I thought that the question was asked previously about any exhaust smoke when cranking, but didn't find it. If there is white and/or whitish-blue exhaust smoke when cranking, then you are getting at least some fuel to the cylinders.
I also wonder if checking another code reader might help. Some are not great at picking up all the codes.
As far as "ether" goes, all I said earlier was to be careful and that I won't say to use it. That being said, supplementary fuel certainly CAN BE helpful in troubleshooting, and brake cleaner or carb cleaner would be better choices.