QuestionI have a 6 cylinder manual transmission 1995 T100. Mostly 20 miles Back and forth to work, mostly rush hour freeway driving. I have been passing emissions for the past 6 years with a bad rear O2 sensor. This year I failed NOX with a 3.01, Phoenix AZ limit is 3.0. HC & CO passed with .17 & 5.43. Toyota replaced both O2 sensors (codes) and plugs and plug wires. Retest resulted in NOX failure of 3.59 and HC & CO increased to 1.3 and 9.16. I checked for any lines that may have come loose ( while in the shop I had a P/S hose replaced) and sprayed around to check for leaks. Engine temp guage reads normal, coolant level is OK, cooling system was flushed 3 years ago. It's going back to toyota next week. Any Ideas?
AnswerWell... That sounds like an extremely gay state! LoL!
The rear o2 sensor has no bearing on anything. It simply tells the ECU when the cat converter is faulty, then trips a light so you know it.
NOX is a sole function of combustion temperature.
Since you've got working main o2 sensors, and new plugs. Check the ignition timing, but more importantly. Take the EGR valve off by hand & clean it. You might aswell clean the idle valve, and throttle plate too - they're all right together & it's basic maintenance on any EGR equipped engine.
Most likely, the EGR valve is sticking closed.
You would be well advised to clean any carbon out of the combustion chamber, as it superheats white-hot & causes pre-ignition of the fuel.
You can do that with putting Seafoam down the intake, or water injection.
On a side note. Flush the cooling system every other year, replacing the thermostat & pressure caps every other flush (4th year), before you cause it to blow a head gasket & toast the #6 exhaust valve from a lack of maintenance. That's a quite finiky engine & you have been inelidgeable for the head gasket recall for almost 2 years now.
