» View Question

sudscap 1/31/2013

1992 Jeep Cherokee Laredo 6 Cyl 4.00L


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 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...

Answer this question

( characters left)

Follow Question

what's this?