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sudscap 1/31/2013
1992 Jeep Cherokee Laredo 6 Cyl 4.0L - Engine
Failed smog, replaced oxygen sensor and cat. Readings were good but NOX to high. Replaced cap, plugs and wires stil high
Running too rich
1 Answer
  • CVO
    CVO 1/31/2013
    NOx (oxides of nitrogen) is a tailpipe emission caused by the oxidation of nitrogen in the combustion chamber. When the peak combustion temperatures go over 2500°F (1371°C) NOx is formed in excessive amounts. To keep the combustion temperatures down, exhaust gas is recirculated.

    Re-circulation of the exhaust gases is accomplished by having a movable valve between the exhaust and intake manifolds. Upon a predetermined demand, engine vacuum is routed to the valve, opening the connecting port and allowing exhaust gases to enter the intake tract.

    Check the egr valve.
    sudscap 2/25/2013
    Now for the 5th time failing smog, I have recently replaced the Intake Manifold Gasket , the Exhaust Manifold, all injector seals, cleaned the whole area , new oil , oil filter, coolant, RUNS A LOT BETTER BUT STILL FAILED WITH NOx levels @ 25mph 1327 way too high. Running out of solutions...

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