1998 Jeep Wrangler Smog Test Failure

REFINEDROGUE

MEMBER
1998 JEEP WRANGLER
6 CYL
4WD
AUTOMATIC
150,000 MILES

I have a 98 jeep wrangler sahara that just failed a smog test in the state of california. I took it to the dealer and he said the #1 cylinder was mis-firing. Would the mis-firing cylinder be the reason for me failing a smog test? The check engine light is not on. And the smog check place I took it to said I might need a new catalytic convertor. The dealer is talking about doing a valve job or something like that so who knows. The dealer said it's gonna cost atleast $1400 if I need a vlave job. Can you please give me some insight or offer me some advice.

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RASMATAZ

MECHANIC
75,992 POSTS

My question is what did it failed on HC/CO/CO2/NOX/O2?

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Friday, May 1st, 2009 AT 9:48 PM

REFINEDROGUE

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It failed HC (PPM) which were at 127 (max is 52) and 113 (max is 36) at 15 mph and 25 mph respectively. Also failed NOX (ppm) which were at 1410 (max is 517) and 1430 (max is 770) at 15 mph and 25 mph respectively as well. The printout I got from the Jeep dealer states code P0301 #1 cylinder misfire. #1 cylinder compression 135 psi. Other cylinders 180 psi.

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Saturday, May 2nd, 2009 AT 1:18 PM

RASMATAZ

MECHANIC
75,992 POSTS

Cylinder no.1 is low can be the cause of the misfire I suggest a cylinder leakdown test.

NOX failures are usually EGR-related, since the EGR system is primarily responsible for reducing oxides of nitrogen. But NOX emissions can also be caused by a bad three-way converter or a computer control system that remains in open loop

Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings.

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Saturday, May 2nd, 2009 AT 2:49 PM