Question1998 4runner failed smog - continued
2 year comparison:
Year: 2002,2004
%CO2: 14.8,14.6
%O2: 0.1,0.6
HC: 4,7
CO%: 0.00,0.00
NO: 690,2200 (GP status)
The scanner says "PASS - no codes returned".
During a later step I accidently left the MAF disconnected and I got a CEL (which I cleared), so at least the ECM is logging some errors. Does no code automatically eliminate any suspects, or could any little vacuum leak be the cause?
I know you suggest EGR problems. This is a 4WD model/w 3.4L and I don't believe there is a vacuum operated EGR valve on this engine. The LH exhaust manifold has an undrilled boss where the EGR would normally go, but nothing is there. I have looked in Motor,Chiltons,Haynes manuals, and they do not accurately describe EGR, EVAP or PAIR on this engine.
The things that I have done:
Replace fuel filter (it did have some crud).
Add fuel injector cleaner to gas.
Remove and reseat ECM connectors.
Check 4 different VSV valves for actuation and leaks (vap pres, evap, 2 for 4wd).
Vacuum @ idle (19psi).
Check both OX sensors:
Both passed heater resistance test (13.5ohms).
Both passed supply voltage test (12.5v).
Voltage output test using slow digital DVM:
The rear sensor behaved exactly as described in my manual.
The output voltage rose from the low mv range to around +100mV while warming up, then began to oscillate between +60mV or so to +900mV when hot (5minutes). The front sensor behaved a little differently, but the engine was not cold.
The output voltage first went negative to about -300mv and then slowly rose to around +100mv, and then began to oscillate between +100mv and +600mv when hot.
Do you think the restricted output range on this OX sensor could indicate a problem?
Removed the airflow sensor and cleaned the platinum wires with a spray contact cleaner.
The one resistance/temperature check I did on this sensor seemed OK. There is no actual
air flow test in my manual.
The one resistance/temperature check I did on the engine coolant temperature sensor seemed OK.
I did notice a lot of soot inside the throttle body, just behind the throttle plate. Would that be
unusual for a car with this many miles or an indication of faulty EGR/PCV?
AnswerThe later versions of these engines did not use the egr system, the combustion chambers were redesigned along with some changes in the computer to keep the combustion process cooler so it would lower NOx emissions so the egr valve and it's components were eliminated, not sure what is going on but the one and only thing that causes high NOx emissions are high combustion chamber temperature, this could be caused by an engine that is running hot or excessive combustion chamber pressures due to excessive carbon builtup, the O2 sensors can not cause this.
