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Topic Review (Newest First)
06-07-2013 01:19 PM
bajajohn
Ca. Smog

Just maybe you should take it to a shop and have it fixed after two fails I would think you don't want it branded as a GROSS POLUTER.
06-06-2013 02:17 AM
2xs
Quote:
Originally Posted by Tomdata View Post
Post o2 sensor and pre cat exhaust leaks only raise nox because they flood the second bed of the cat with o2. Has nothing to do with what's going on inside the motor.

Again... You WILL see 3-4% o2 on the printout if that was happening.

The laws of chemistry always win
The front bed of a three way Catalytic Converter (TWC) contains rhodium to reduce Oxides of Nitrogen, “Nox” it does this better when the air/fuel mixture is slightly rich.

The rear portion of the Catalytic Converter is to oxidize HC and Co.

When your O2 is used up completing the HC and CO reduction, your O2 disappears....

This is why you wont always see the "3-4% o2 " you are referring to.

See, you are correct, Chemistry in action....
06-05-2013 10:11 PM
Tomdata Post o2 sensor and pre cat exhaust leaks only raise nox because they flood the second bed of the cat with o2. Has nothing to do with what's going on inside the motor.

Again... You WILL see 3-4% o2 on the printout if that was happening.

The laws of chemistry always win
06-05-2013 08:49 PM
2xs Thats great, but that NOx is affected by more then whats listed on that graph.
Drop in some hotter range plugs, or work on a vehicle where some dope couldnt get a leaking freeze plug out and pushed it in and installed one over it creating a hot spot, BANG! you have a NOx issue thats totally not related to your basic graph....

Now go run your basic smog inspection, put the result aside, then drill a hole in the exhaust (after the O2, but before the Cat, rerun the SAME test, look at NOx, guess what, BANG! higher NOx, another result not related to your Graph....

Yes, I have seen this happen, at my last update class we actually did this, hole in the exhaust test, and it was amazing, turned a OBD2 Malibu from a good runner into a Gross Polluter for NOx....
06-05-2013 09:58 AM
Tomdata We are way off topic now.. but since we are lets get back to the basic chemistry of a gasoline internal combustion engine.

Afr emissions graph. (Same as the one in every smog tech training manual)
06-05-2013 02:45 AM
2xs
Quote:
Originally Posted by Tomdata View Post
An exhaust leak before (upstream) of the o2 sensor will cause it to run rich and fail for high co/hc. Nox will be close to zero in a rich condition.
Not enough, as O2 will completely render the NOx bed inactive in a Cat. Remember NOx is created by HEAT, the only reason NOx is thought to be lower in a rich condition is because you run HOTTER during a lean condition, but if you are running rich, high compression caused by carbon or other deposits can also cause high NOx...

Please use CAN instead of WILL, I have seen TONS of cars out there that CAN prove you wrong.
06-04-2013 09:18 PM
Tomdata An exhaust leak before (upstream) of the o2 sensor will cause it to run rich and fail for high co/hc. Nox will be close to zero in a rich condition.
06-04-2013 09:13 PM
bajajohn
Leak

Quote:
Originally Posted by redneckbrat View Post
I believe I have a leak. Thought this for a long time. I'll have to check for that.


The 4.0 is famous for exhaust leak at manifold and exhaust pipe some times you cant hear it just replace the donut style gasket.

I have a 91Y J before I smog it I fill it with premium and take it to the freeway and run it pretty hard then go directly to the smog sta. and have it smoged
06-04-2013 08:45 PM
Tomdata Exhaust leak would show at least 3-4% o2 on the printout.
06-04-2013 07:34 PM
redneckbrat
Quote:
Originally Posted by 2xs View Post
STILL, OP, check your exhaust system for leaks, you might not even be able to hear it, but if there is a leak, FIX IT!
I believe I have a leak. Thought this for a long time. I'll have to check for that.
06-04-2013 04:10 PM
2xs
Quote:
Originally Posted by Tomdata View Post
Also.. On older jeeps the cat is soooo far from the motor it will take a lot of preheating (racing engine at 2500 rpm in neutral) right before the test to light of the nox bed of the cat.

Before they made it against the rules, we used to drive them around the block a time or 2 in 1st, hit 4K most of the trip, between Jeeps and the Hondas it usually got them IF the NOx bed was good in the cat...

Quote:
Originally Posted by Tomdata View Post
I have had my ca smog license since 2002 and tested thousands of cars

Your catalytic converter is bad.. 99% chance you have some generic replacement cat welded on there based on the readings. Make sure you get an obd2 compliant car and it will pass all zero's.
Because of the poor cylinder head design an no egr system these motors need a good catalytic converter to eat up nox.

Been a smog tech in Cali since 92, as long as there is NO exhaust leak before the cat, then there is a good chance his cat is bad, but even a small leak will render the NOx bed portion of the cat useless.

STILL, OP, check your exhaust system for leaks, you might not even be able to hear it, but if there is a leak, FIX IT!
06-04-2013 05:52 AM
Tomdata 4.0l jeeps are notorious for nox issues. Modern catalytic converters have two separate catalyst beds.
One bed reduces hc&co when the o2 sensor switches lean and the second bed reduces nox when the o2 sensor switches rich. Low hc/co does not mean the second bed (nox bed) of the converter is good.

If you do not have the proper sized/rated catalytic converter it is impossible to reduce the nox on a 4.0l.
Using octane booster,race gas (octane booster) colder spark plugs, retarding ignition timing, sea foaming the engine, etc are all just ways of band aiding the real problem. Also.. On older jeeps the cat is soooo far from the motor it will take a lot of preheating (racing engine at 2500 rpm in neutral) right before the test to light of the nox bed of the cat.
06-04-2013 03:14 AM
bill8bud
Quote:
Originally Posted by Tomdata View Post
Your catalytic converter is bad.
That is what I was told put in a walker direct fit cat and it did nothing for my numbers.

The manager of the smog shop said the same thing new cat you will pass. I failed I think that is why he gave my 4th test to me for free.

I think I pulled a perfectly good cat out.
06-04-2013 02:52 AM
Tomdata I have had my ca smog license since 2002 and tested thousands of cars

Your catalytic converter is bad.. 99% chance you have some generic replacement cat welded on there based on the readings. Make sure you get an obd2 compliant car and it will pass all zero's.
Because of the poor cylinder head design an no egr system these motors need a good catalytic converter to eat up nox.
06-04-2013 02:40 AM
st1264 Buy this stuff and stop spending money on your Jeep (as long as you're not a tree hugger). They sell this stuff here in Canada that is supposed to guarantee a PASS to Emissions testing. Our emissions are similar to California. My friend used it on his modded Camaro to get a pass.

Guaranteed 2 Pass Emissions Test Formula | Canadian Tire

I've always had V8 pickups and SUV's and have never failed a smog test ever. Good running motor with a working Cat should get you a pass. If not, buy that stuff ^
06-04-2013 02:12 AM
bill8bud I did a couple of things before the test. I added Octane boost and a new O2 sensor from Bosch. I drove it for 30 miles filled up with more 91 octane gas and ran for another five miles and took it in.

NOx was at 0:highfive::highfive::highfive::cheers2::cheers2:: 2thumbsup:



The 15 MPH test was completed in 18 seconds instead of running the full 90 seconds like on the previous test. The 25 MPH test was completed in 20 seconds.
06-04-2013 02:11 AM
bill8bud I had similar numbers on my Jeep a few weeks ago.

Lets lay my cards on the table with all the test results I have been so happy to gather.

Test 1 5/11/12
Items I did before the test:
Replaced air filter
Drove Jeep around for 30 minutes freeway and city driving.
Added 1/2 gallon of 91 octane fuel to a full tank of of 87 octane fuel



Test 2 5/16/12

Checked CEL codes code 11 changed ECT Engine Coolant Temperature Sender
Changed oil
Warmed Jeep up for test.



Test 3

Seafoam fogger used
Replaced CAT
Warmed Jeep up before test



No new CEL codes
Checked fuel pressure while running 32 PSI (Loaner tool 1 did not show any presure again. Replaced loaner tool 1 with loaner tool 2 and it shows 0 psi.

Cleaned throttle body it was dirty

Going to see if loaner tool 3 is available at AZ

Fuel mileage has improved from 11 to 12 to 15 to 16 MPG



Now I did the following and dropped my NOx to zero
06-04-2013 01:58 AM
redneckbrat I did run with a bad O2 for a while until I figured out what was wrong. I believe it has the original cat. I'm trying to find an inexpensive replacement for the cat.
06-04-2013 01:22 AM
2xs 5015:
14% CO2 = rich
1.52% O2 = too high (weird, You normally see this with a misfire or exhaust leak before the cat, but you would have it high at 2525 also)

2525:
15% CO2 = lean
.01% CO = lean

Do you have the original cat?
A bad O2 can take out a cat, so if you were running around with a bad O2 you could have taken out or weakened the cat.

Ideal number for the CO2 is 14.7% (perfect mixture).
the HC (Unburned fuel), CO (Partially burnt fuel), and NOx (O2 and Ni combined when too much temperature is present), averages are listed for your Jeep, and should match, but dont always.
06-04-2013 12:14 AM
redneckbrat Hope this helps.
06-03-2013 11:18 PM
2xs Excessive heat caises Nitrogen and Oxygen atoms to combine forming NOx, Usually the result of a lean mixture, higher compression, or an exhaust leak before the cat converter.
Or a malfunctioning EGR (which you do not have), or an AIR pump pumping air into the exhaust before the cat converter (another thing you dont have to worry about because you have no AIR injection).

Please post an image of your emissions test report, dont leave any info out, no matter how inconsequential you might think it is.
06-03-2013 11:13 PM
redneckbrat
Failed Smog for the second time.

It's better now that I changed the O2 sensor. Now my NO(PPM) is too high. Anyone know what causes this and how to fix it? thanks

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