97" 540IA mystery with the check engine light

[ClaytonP]

3 years of no one able to solve it, so would anyone of you have a better guess?
Background: shortly after both cats were changed the diaphragm blew up; so, tons of smoke went off.
- Then only after months of intermittent backfirings the check engine light began to appear
- changed one cat, eventually, to see if it helps, although many people suggested not to change the cats, contrary to what the dealer recommended; these guys said that the excess of the oil will burn out; since that change (1 cat replaced) was done the rather huge jork the car used to have disappeared; so, the jorks became lesser, but the light continues to come up
- after over two years of watching the pattern the following seems to be taking place anyway:
- the light appears invariably at the speed between 60 to 80 km/hour; as odd as it may seem, most of the time the vehicle is going uphill
- what follows is a short jork, nothing from the exhoust, but the light comes up and lasts for days or weeks (I often thought about the trans which otherwise is as a new one)
- no red flags from the software
- one exception is the ratios pertaining to the three out of the eight cylinders (on both sides) as larger, i.e. they work harder
- all the sensors seem to be intact if one trusts the software

I asked my mechanic to think about luqid oil still being in one cat, so when the vehicle is not horizontal, the level of the liquid oil in the cat closes the opening, thus is the jork; my guy laughed at me and said that because of the temp in the cats it's impossible

Am I being wrong/cheap by not changing the second cat? Is it possible there is something else going on? one fellow suggests that there is a... sensor,, forgot what the hell it was... any way; would Anyone be able to share some thoughts?
Thanx

[DiagnosticToolDave]

I use a diagnostic tool called CarMD. It will pretty much tell you whatever is wrong with your car as long as it is a 1996 or newer. It costs about $90 and*it plugs into the On-Board Diagnostics (OBD-II) port. Very easy to use. Heres a link to the site if you want to check it out:

CarMD - The easy-to-use handheld automotive diagnostic tool and software package

[benzin]

This is the best Program out there,If you have a computer or laptop.

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[Dirty_Tool]

you didnt mention what fault codes its storing...?