88 mustang error codes

The others are TAB and TAD, right?

Do you run a functional AIR set-up? If the TAB and TAD aren't connected (the air pump hoses themselves don't matter, nor do your passages on the heads), it can toss a code. Jrichker has posted the resistor values needed to try and trick the CEL.

Good luck with the sniffer.

Since the AIR system is still basically functional, give the TAB and TAD a once-over (you're right - Thermactor Air Bypass and TA-Diverter). As I recall, you should see 12 volts at the red wire and the other wire is controlled via the computer (via a ground pulse). You can see if the ground signal every comes or disconnect the electrical connector and bench test the solenoid to see if it actuates when the ground pathway is provided.

Jrichker has a nifty write-up on these codes if you want more info.

Good luck.

You could do what you propose (be SURE to keep the check-valve in the plumbing to the air pump no matter what you do. It saves the head of the pump in the event of an afterfire).

I know for me, they check my SMOG solenoids pretty closely to ensure they are there (I run all OEM smog stuff). Otherwise, you could run direct air (through the check valve) to the cats like you propose. Creative hose work could make it look almost OEM (not that we'd ever want to fudge emissions equipment - we're talking about things for you to do for off-road reasons only, of course ).

I would rather leave all the stuff functional. Unfortunately you might have had a hose come loose at the back of the heads . That would be the only thing disturbed and your cats would get their air supply just like OEM (and 99% of the time).

There are a few ways to do it. You know how the system works so just do what seems best logistically.
Good luck.