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Emissions failure #2

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1 year 4 months ago - 1 year 4 months ago #58753 by 99BlackPearXJ
Hello all,

I had recently taken my automatic 99 jeep xj cherokee 4.0 into the CO emissions testing. It failed with High HC (.97gpm of .8 allowed) and Nox (5.1gpm of 1.5 allowed).
My last emissions test two years ago I passed with no issues what so ever, nowhere close to failing. I had a thief steal my catalytic converter this year and I put a cheapo amazon one on the jeep for the time being. Beyond that nothing has changed on the vehicle.

After the first emissions failure I hooked up an obdii code reader to verify the O2 sensors voltages were not (frozen) nor violently fluctuating, they were reading smoothly (newb here). The system is going into closed loop and the throttle position sensor was reading consistently as it opened an closed, this was consistent with a throttle percentage and voltage reading. I did not check the sweep with an analog meter as I don't believe the ecu was thinking it was stuck in wide open throttle and it went into closed loop once warmed up.
I also pushed some air through the tailpipe to search for exhaust leaks and I found the exhaust header to be cracked along a weld so I replaced that yesterday and took the jeep back to retest today. After a new header, air filter, some seafoam in the oil, fuel and through the throttle body, I filled up to a 1/4 tank and headed to the facility.

Again it failed, Hydrocarbons came down to (8.3gpm just shy of the tolerance of 8.0gpm) and the Nox stayed almost exactly the same at (5.06gpm of the 1.5gpm) tolerance.

I plan to check spark plugs and change the oil after I let what I added run through a bit. I have not done any compression or vacuum tests nor have I popped the cap/rotor to see its condition. I have no overheating issues what so ever, the radiator has had the trans lines bypassed so its only running coolant through.

Would anyone disagree that this is probably a catalytic converter issue?

I'm clearly a bit out of my knowledge base so If there are more thing or anything that I should be checking, could you please recommend to me a list in order of what I can be doing to further diagnose this issue?



Thank you all
Last edit: 1 year 4 months ago by 99BlackPearXJ.

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