Jeep failed smog test...need help!!!!

[4x4 XJ]

I need some help here guys.. I took the jeep for a smog check and I failed the 15mph NO PPM test.. can anyone give me any advise what its causing to fail at 15mph and not 25mph...
I have a 2000 XJ sport with 201K..it has brand new plugs, and fresh mobile 1 oil....
Thanks in advance.

Here are the numbers

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[mako my day]

EGR, or a vacuum line loose possibly.

 

[4x4 XJ]

But the newer xj have no egr correct. ..

 

[mako my day]

No idea

 

[GrimmJeeper]

no EGR.

high NOx is due to combustion chamber temps, you most likely have either a vacuum leak causing it to lean out or carbon buildup on the tops of the pistons raising compression ratio, i'd lean towards the carbon with how many miles are on it. run some good injector cleaner through there (lucas or Amsoil) and/or seafoam it.

 

[4x4 XJ]

no EGR.

high NOx is due to combustion chamber temps, you most likely have either a vacuum leak causing it to lean out or carbon buildup on the tops of the pistons raising compression ratio, i'd lean towards the carbon with how many miles are on it. run some good injector cleaner through there (lucas or Amsoil) and/or seafoam it.

I just did the seafoam and it smoked really bad..hopefully this will fix it....

 

[mako my day]

Nice Keep us updated.

 

[4x4 XJ]

Also does anyone know if the CO reading off 0.01 is normal...just wondering since the numbers are so low...

 

[Ex Jay]

yup thats normal.

Other things that could cause the lean condition would be the O2 sensor and coolant temp sensor.

Oh and dont disconnect your battery between now and the re-test if you can help it. You need to get a few drive cycles in to solve that OBD fail

 

[4x4 XJ]

yup thats normal.

Other things that could cause the lean condition would be the O2 sensor and coolant temp sensor.

Oh and dont disconnect your battery between now and the re-test if you can help it. You need to get a few drive cycles in to solve that OBD fail

I found out about batt disconnect the hard way.... on the O2 sensor whichone would it be there's 4 of them...

 

[GrimmJeeper]

on the O2 sensor whichone would it be there's 4 of them...

the only way to tell that would be to have someone put it on a scanner that can read live sensor data and see if one of them is reading out of spec once it gets to operating temp.

do you have a gauge for the coolant temp or the dummy light cluster? as Ex Jay posted a bad sensor could cause the computer to lean out the fuel mixture as well, and if you have the dummy light it could be going out and you wouldn't know because you dont see the reading its giving.

 

[4x4 XJ]

the only way to tell that would be to have someone put it on a scanner that can read live sensor data and see if one of them is reading out of spec once it gets to operating temp.

do you have a gauge for the coolant temp or the dummy light cluster? as Ex Jay posted a bad sensor could cause the computer to lean out the fuel mixture as well, and if you have the dummy light it could be going out and you wouldn't know because you dont see the reading its giving.

I have a gauge for temp...

 

[SanDiegoXJ]

I used to fail smog with similar numbers. I eventually had it cold tested to pass it...but, I was able to bring the nox down a lot by just sealing up little holes in the exhaust...just replaced the exhaust and found a significant hole on the top of the downpipe...curious how it goes this time.

 

[sidewaysstarion]

Well there are 2 places NO can be created, 1 in the combustion chamber due to high combustion temps and in the catalysts due to high cat temps. High combustion temps can be caused by lean mixture (bad o2 sensors, manifold air leak, etc), or a build up of carbon in the cylinders. High cat temps can be caused by a lean mixture or air leaking into the exhaust through a leak somewhere.

 

[4x4 XJ]

Here's and update , I did the seafoam thing on the break booster, I took the TB and IAC sensor to clean them.I checked all air hoses for any tears or leaks...changed sparked plugs and added an injector cleaner to a full tank of gas... and put the OEM airbox back in...

I will take it back tomorrow for a retest and see what happens

 

[Ex Jay]

I dont know if I would smog it with the injector cleaner still in it. Ive heard mixed results with that. Id run through that tank, top off again, and then smog it.

might try that "gauranteed to pass smog" stuff or an octane booster. Octane booster should help with the lean condition. Not a real fix but worth a try.

 

[conejocherokee]

I had the same problem on my 1996. I did the following with little improvement:
Straight 100 octane fuel
Sea foam
Cold test
Hot test

What worked...
Cooler spark plugs Champion RC9YC
Sealed the leak in my exhaust with hi temp silicone just prior to the test.

Correct me if I'm wrong, but shouldn't a properly operating cat be turning out lower O2 numbers?

What really intrigues me is why my 2000 Federally certified 4x4 XJ wasn't tested for NOX when I bought it 6 months ago

 

[4x4 XJ]

I took the retest today.and it pass perfect..

 

[Ex Jay]

glad to hear it! Now go hit the trails!

 

[4x4 XJ]

glad to hear it! Now go hit the trails!

I will be outthere on sunday...wooohooooarty: