I would make sure it didn't jump time on the cam belt. Check compression and check the alignment marks on the pulleys. One tooth out and exhaust valves open soon or close too late and combustion goes out the pipe..very bad for exhaust valves so please check that timing is correct. One tooth off and it will actually run half decent but noticeably lack power.

The O2 sensor could be bad, maybe cause a lean condition or a rich one but in your case with sooty plugs, it's definitely running rich or LOW compression if it's out of valve timing. A clogged up sooted O2 sensor makes it run RICH.

I think I have my IR temp gun where I can find it, will measure my temps for you around the exhaust. The manifold is well over 500F I'd expect and the downpipe to cat can't be far behind so you may be worried about heat that turns out to be normal. I'd focus on the valve timing, the O2 sensor and the fuel pressure regulator and if you happen to fix something there, the rest of your probs may vanish. I set my ignition timing to 12deg BTDC. Dunno if it is spec but it runs well there..

The fuel pressure should be around 24psi at idle with normal vacuum. Running down the road and easing in full throttle should ramp you up to 36 to 38 psi on the fuel rail.. I suppose in driveway, blipping the throttle in park/neutral should give you same results. Check before you replace regulator or other...

How to measure fuel pressure???? Don't even THINK about getting the goofy metric unobtainium fittings... just break the connection to the rail and slip some 1/2" fuel rated hose over the connectors and use appropriate hose clamps and tighten 'em up.. The feed line male connector side may need 3/8" hose but I did it with 1/2"... make your Tee barb fittings in the middle of the hose to your gage. 1/4" galvanized pipe nipples fit right into 1/2" hose and you can plumb the pipe nipples into appropriate galvanized Tee and off to your gage..
Cost is practically zip and IS zip is you have a good junkbox of old fittings..
I have used my AC gages for this with no ill effects.. let 'em dry out well afterwards that's all...
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Genesis 7:11