| High Monoxide Levels are usually an indication of Rich Mixture. if you have an injector problem, (where they are not putting out the same amount of fuel ), then you will get improper fueling among the cylinders of that bank.. Hc's are also high, indicating a rich condition.. A lean Missfire will also cause High Hc's.. Have you actually looked at the AFR's or watched the O2 Cycling ( Above/Below .5 Volt ).. the Speed of the Cycling will show you if the ECU is 'Happy' with the O2 Sensor Readings.. and how hard it's having to work to get the fueling Proper.. I do not know what the 'Cycling Frequency' should be of the O2's at Idle on the Z.. but other cars I have worked on like to Cycle at about a 2 second rate.. ( at Idle ) that would be Crossing from Below .5 to above .5 every second, then crossing back from above .5 to below .5 every second. When it falls off to every 5 seconds or so, the AVERAGE Mixture on that bank is not proper... it's still able to get the mixture to the 14.7 number, but only for a brief moment, the rest of the time the mixture is out of speck, and will not pass smog.. I think the ECU can be put into a test Mode, where it will Flash Rich/Lean on the LED's.. Have to check that further.. FSM I think it's in there.. you would be counting the Flashes. ( I think ) Are your cats HOT.. if they get a chance to cool off, then they are not functioning.. So far, you've done all the right things.. just has not worked.. ( yet )..
I think it all boils down to, Are your Injectors any Good?.. have they been Cleaned and checked for Flow and Matched in the Banks?..
If it was my car, I'd toss widebands ( Temporally ) on the Left and right banks, and look at the fueling ( I like LC-1's in the Factory Bung, and use the Narrow Band output to drive the ECU.. PITA to wire but no welding.. ) .. and that would still only give me a SLIGHT clue as to what was going on.. as the Widebands will be seeing a combined flow from 3 Cylinders.. some could be lean and one rich, and the Combined flow will still be proper.. ( The LC-1 can actually see individual Pufs and do a AFR on them, but it is more than the Usual gauge or Lap Top can do to see the Individual cylinders firing.. ) How is the Compression? do you have any leaking Valves.. That will cause High HC's.. If your car Idles good, then LIKELY not a valve problem.. but I'd also check compression.. It's like Blood Pressure on a Person.. gives you a Clue as to the health.. Not sure if a cylinder balance test will tell us anything.. as if it's bad, then Likely the Injectors would be the Culprit.. but if the Test is Good, then Injectors are the only thing left to test..
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