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Past couple of weeks I have noticed that the tailpipe is sooty black inside, not the clean to charcoal gray that it has been for the past 15 years.
Oxygen sensor and fuel pressure regulator are both original, 15 yrs and 225k miles.
Seems to run fine, have not checked mileage, but presume it is down, since the tailpipe indicates I am running rich. I hope I don't cook my old catalyst.
What do you guys think is the most likely culprit?
Should I just order the oxygen sensor and fuel pressure regulator as standard maintenance before seriously trying to diagnose the problem?
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