My 95 sport with an AW4 and 144k miles on it failed the smog test only in the NO ppm section.

Results:
......................CO2.....O2.......HC......... ...CO%..........NO ppm
...........RPM.......................max_meas...ma x...meas...max meas
15mph..1641... 15.20__0.09__63__5_____0.46_0.00___460_760
25mph..1638... 15.20__0.08__38__2_____0.56_0.00___539_678

I have a 99+ intake with 703 injectors, had the head off for valve job 2 yrs ago, replaced cat and O2 sensor 2 yrs ago and barely passed smog then. Other than that it seems to run perfectly.

Any help would be greatly appreciated... if i left out anything let me know.

Thanks in advance.

 

Might be the charcoal canister

 

common problem on OBD1 jeeps. change cat. need 3 way cat. stock wasn't made for nox. I use magnaflow and have gotten 2 jeeps to pass. Make sure you get the california model. if you have lots of money you can get a dealership cat for about $700 last time I checked. magnaflow was $250 last year.

 

I will look at getting a charcoal canister... is there anyway to test the one i have?

And i will be ordering another cat. I just put a magnaflow cat on 2 yrs ago.

I really hate California!!

 

Excessive NOx means the combustion chamber is too hot.
If it has EGR, check that.

Wrong plugs, especially the "trick" plugs can cause it.

Use the Champion plugs called out on the underhood label - not what the parts idiot says.

Nothing to do with the charcoal canister

 

X2 on the EGR system.........High NOx has nothing to do with Charcoal canister, or Cat.
System is designed to re-route some of your exhaust gas back into the intake to cool your combustion chamber temperatures

Check all vacuum hoses leading to EGR solenoid, and EGR valve(make sure you get vacuum in the hose with the engine running) EGR solenoid only operates at certain part-throttle engine speeds/loads...........Then check to make sure EGR valve isn't stuck closed(sometimes you can move the diaphragm with your finger, others you'll have to unbolt it from the engine 1st) If you have access to a hand vacuum pump, check it with this.
then check the EGR passage isn't blocked with carbon or oil gunk buildup.

 

95's dont have an EGR...

 

x2

EGR's on the XJ's stopped with the introduction of Chrysler OBD I. Only Renix XJ's had that piece of..... poo poo (thank God).

IIRC, the EGR's main function was to introduce exhaust gas into the cylinder chamber to cool it off for NOx (how that works, I haven't the slightest). IIRC, the 91+ XJ's used exhaust valve overlap of some sort to keep some exhaust gasses in the combustion chamber, allowing elimination of the EGR. I may be wrong though, someone correct me if I am.

Are you running lean? A lean condition would cause excessive temps, and I know for a fact that OBD I computers don't exactly watch O2 sensors like a hawk (mine somehow got knocked unplugged, and I never got a CEL. Only found out when I swapped my header in). Also, just a long shot question, did you make sure your engine was up to operating temps before you were tested? I hear a lot of guys who say doing so allows for better results. Hopefully someone with more info can chime in to help.

Threads like these make me pray thanks that we don't have that bullcrap testing here in Shenco.

 

On older engines combustion temps were around 3100-3200 degrees.

NOx forms at about 3000 degrees and above. (An atom of Oxygen "welds" itself to a Nitrogen atom. They can make 13 different combinations - isotopes, that why it's called oxides of Nitrogen NOx - some are harmless, some are deadly.)
A small amount of burned exhaust gas is introduced into the camber to dilute the mixture slightly, lowering the temperature enough to reduce Nitrous Oxides. All it takes is a little.

Initially small holes between the intake and exhaust were used called Floor Jets.
Next stage was use a valve to recirculate a little - EGR Valve. It had it's troubles and the unknowing disconnected it.
Then the cam grind was changed slightly - the exhaust valve closes slightly earlier to trap a little exhaust in for the next stroke.

At any rate, the cylinder temp is slightly too hot. By his numbers the NOx is close, it won't take much to get it down.

If it was too lean HC would be kicking up - it's not.

Old worn plugs, or the wrong plugs can make it too high. ALWAYS use the plugs called out on the underhood sticker - the engineers that designed the combustion chamber knew what they were doing.
Fools at parts houses, the internet, the neighbor, or what was in there when you got it have no idea. Often they will actually destroy an engine because of inaudible ping.

A small chunk of carbon can glow, causing slight pre-ignition, raising the temp.
Before changing plugs, add a can of Techroline to a 1/2 full gas tank. Drive it till it's near empty.

Put in the new CORRECT plugs. Just before you take it to get it tested again put in new fresh gas (they have the additives it needs - they evaporate within 1 or two weeks - FRESH!)
-- AND - put in a 1/2 pint of denatured alcohol - available at hardware and paint stores - $1.00?

If it still fails you may need to go with a 3 way cat - dealer's are too expensive, ordering on the internet is usually not what you need, Chain muffler shops will rip you off - Midas etc.
Go to a smog station and ask - they usually know the cheapest quality independent muffler shops to get them.

Let us know!

 

Thanks for the help. This has been exasperating trying to figure out whats wrong.

2 years ago i let the parts idiot talk me into autolite platinum plugs... those will be coming out and the standard Champions as listed under the hood will be going back in.

I dont think its running lean... is there any way to test a/f mixture other than getting/renting a wide spectrum analyzer ?

Just added info, i have the 99+ intake, borla header, magnaflow cat and cat-back system, the turbo city rock-it tube air intake, and Neon 703 injectors that were soaked in sea-foam.

Thanks again

 

what I see with all the add on stuff is your running lean. If I remember the neon injectors are 23lbs. should of helped. carbon in the head can cause problems. can you raise your fuel rail presure a few lbs? other thing is what O2 sensor did you put in? cheapest autozone or OE? had some problems with poor quality parts.

 

It was just tested for lean by the smog station - your smog numbers don't indicate it's too lean.
If it was too lean it would misfire a little - HC would increase.

 

The O2 sensor was an OE style from Napa. Would it help to richen up the
a/F mix ? Would that lower the NO ppm even if it elevates the HC a bit? I saw on a thread about a Chrysler fuel pressure regulator that runs around 43psi, does anyone know what vehicles that comes from ??

Thanks for the help.

 

Change the coolant and run a 70/30 ratio. More water will cool better and faster, that will help keep the combustion temps down. rrich has a some very good info and is spot on. You don't need to start throwing new injectors and charcol canisters at this thing, just install the correct plugs and change your coolant ratio.

 

to pass Calif smog I've tried every crazy thing you can think of. did straight water and water wetter doesn't help. as far as raising fuel pressure. there is some requlater that swaps, but you'd be better off buying the Hesco adj. regulator. What might work is get some cleaner to clean out any carbon that might be in the head. use chevron gas.raise fuel rail pressure to about 35 for the test. you could also put a restrictor behind the header. about a 1 3/4 reistriction to raise back pressure. for test only then remove. or water injection which will lower nox. I have passed doing some of this stuff but found by just putting the right cat on worked the best.