Quote:
Originally Posted by 911boost
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(WAG here)
The high CO = Way too rich of a mixture, or oil is present.
There is too little oxygen to turn the burn the mix into pure H20+CO2. A bad head temperature sensor or O2 sensor might be keeping the fuel trim in Open Loop (the startup rich mode where the computer doesn't pay attention to the O2 to lean it out).
The high HC = A dirty burn.
Raw gas or oil vapors are being pumped out the exhaust and even the CAT can't burn it all up. That can become too much for even the long-term fuel trim to compensate for. The tailpipe after the CAT should be 50-150deg hotter if it's doing its job. They do get contaminated with silicone from sealants, get gummed up from oil, or just wear out.
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I'd first suspect very high fuel rail line pressure or a leaking injector(s) on the fuel side. A bad plug might also be sending raw air downstream, then the O2 'sees' this and richens up the mixture, making the entire system worse. An EGR not closing can do the same thing somewhat. Or a gunked up MAP/MAF could be telling the computer to pour in the gas.
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I'd suspect leaking valve guides/seals or sticking oil rings on the oil side. You are still getting good performance so the compression rings and ignition system are mostly doing their job.
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To be sure of what the computer is seeing , it might be best to drive it around with a
https://www.bing.com/search?form=MOZTSB&pc=MOZI&q=obd2+scanner hooked up to the 16 pin OBD2 port which is probably located under the left dash. This will help tell you what the computer inputs are saying, especially for open/closed loop function, MAP/MAF ranges during operation, and the O2 readings which are either dead or off the charts. Just remember a thrown code is only what the computer sees and is not necessarily the true source of the problem.
A stuck-open injector might show up as a bleeding-down of line pressure at the fuel rail a little while after shutdown. If it's just worn out and dumping fuel like an open hose-end instead of spraying in a droplet cone pattern, comparing the plug conditions will show which cylinder is getting carboned-up.
Oil treatments such as
https://seafoamsales.com/knowledge-base/how-to-add-sea-foam-motor-treatment-to-crankcase-oil/ need to done carefully with an oil change afterwards, and may gunk up an already borderline CAT, but will clean out carbon deposits and un-stick rings and valves. This may create a dense smokey fog throughout the entire neighborhood as a caveate. Higher consistent revs on the freeway will also give it that "Italian Tuneup" and should done once in a while anyways.