mjeds

I never got a code, or a check engine light, before or after changing the O2 sensors.. what lead me to the cat was a high hydrocarbon reading when I had it smog tested for registration, while it passed it was only 1 point under the max.

the cat wasn't clogged it was broken, came apart in 4 pieces when we removed it, the only thing that was holding it together was the rust, damn casing was rusted completely through and the ceramic material inside was in chunks, not dust, so it was blocking flow, not clogging it. after replacing it the power loss was gone and the hydrocarbon reading went from 60 (61 is max) to 17 (14 is normal).

Hanxious

pbxcomm

Looks to me from the pics that you have some detonation going on by the looks of those plugs.
So, what type of fuel are you running, consistently?
Have you checked the gap of the plugs (they are gappable and must be gapped prior to installing them).
You may need to run some diagnostics to check timing if its bouncing around.
Engine Temperature? Has it increased as of late?
Have you run any fuel cleaner (Seafoam)?
May want to check your fuel Injectors.
Lastly, you may have some significant back pressure from your mid pipe and/or axel back.

Hanxious

-I run 93 Octane from Exxon.
-I haven't checked the gap. Since the shop possibly installed the wrong plugs (IKBH20TT) I am replacing them this weekend with FK20HBR11 after the top engine clean. (weather permitting)
-Temp has been steady in the middle.
-I have run Techron in the gas tank

Do you think back pressure would cause the rpm drop and power loss? It's not there everyday, and only happens under 45mph and under 2000rpm. On bad days around 3rd and 4th gear, it'll drop to 1200 rpm while accelerating and be sluggish. After giving it more gas to compensate, it will jump up to where it should be around 2500 until its in 5th and at a higher speed.

Sodium

Excessive back-pressure can cause power loss – more energy is required for the piston to push out the exhaust gases during the exhaust stroke. But you're going to be doing a lot to your car in the near future, so no point in worrying about back pressure unless you still have the problem after the top engine cleaning, tranny fluid exchange, and everything else you mentioned above!

Also, to expand on what pbxcomm said about spark plugs, here's a guide for reading the appearance of your spark plugs: https://www.ngksparkplugs.com/about-...d-a-spark-plug

Hanxious

Well I finally got a code P0430. It came on as I experienced the typical power loss/shudder.

I doubt it is exhaust leak related since I'm also experiencing the power loss and strange shift points, correct?. I would really like to keep the car if this fixes the issue, but I'm still going though a qt of oil every 600 miles and I don't know if its worth the engine rebuild, and possibly the ECU or whatever is causing the car to possibly run rich.

What is the likelihood of the Cat temps causing transmission problems?