mercury cougar 1996 p0155, p0156, p0161 together

Hello, I have this cougar with a 4.6L V-8. These codes pop up almost immediately after I clear the codes. After a while I usually get the p0306 misfire on #6 with a blinking check engine light. The car has an erratic idle that seems like a misfire at idle. When you accelerate from a stop, it seems to be smooth until 1/2 up the RPM range from take off...then seems to struggle.

I have changed the plugs, wires, coil packs, fuel filter, air cleaner, MAF. Compression is good...which means no difference between #6 cylinder and the others. I have smooth vacuum gauge needle. This car has a primary CAT off each manifold, and share a secondary CAT; which has 2 inlets and one outlet. The secondary CAT is gutted...it was opened up, the guts removed, and sealed back up.

Since the three codes indicate O2 circuit failures, my questions are these: 1. where is a fuse that controls these O2 sensor circuits? 2. Would these codes and their cause, also cause the erratic idle and performance issues I have? 3. could the second CAT being empty cause these codes? 4. What else could this be? Injector? plugged primary CAT? something else entirely?

thanks

I am not at work so not sure of fuse location but on this model with the 4.6 I have seen a few PCM's go bad for the O2 driver that controls the heaters. You need a scan tool with bi-directional controls or you can check it when the engine is cold but I get a light socket like for a brake or turn signal and attach some extension wires then connect the bulb to the o2 heater circuit(power and ground) and see if it lights up when you start it if it does not and you are getting power and the ground circuit is good to the pcm then the pcm is bad. A voltmeter is not a good way to test this because the meter does not produce a load and the light bulb does. Chances are that you can use a meter and will see voltage but as soon as you load it up the voltage will disappear.