This is topic smog check, failed NOx 93 jeep grand cherokee in forum Tech Talk at Northern California Ford Owners  .


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Posted by 66 AC COBRA (Member # 904) on :
 
my girlfriends 93 grand cherokee Inline 6 failed smog today

it passed hc and co but failed NOx, what would cause this, anything to look for

the cat is not even 2 years old, the plugs, cap, and rotor have 5000 miles maybe

i dont think it is a missfire because the hc and co2 passed fine, NOx was almost double the max allowed

could a o2 sensor cause this, maybe check the egr for operation??
 

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Posted by blind (Member # 3052) on :
 
NOx is usually from the car running too hot
 

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Posted by 66 AC COBRA (Member # 904) on :
 
car runs at 195, right where the thermostat opens

I am gonna clean the egr, test the o2 sensor, and put some premium in it and see what i can get out of it on a pre test, fun times
 

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Posted by hidnn.o.s. (Member # 1219) on :
 
Eric, isn't one of the "secrets" to passing smog to have 1/4 tank of "87" octane
 

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Posted by 66 AC COBRA (Member # 904) on :
 
maybe if it was an hc or co problem

NOx is a higher than normal combustion temperture, like its running lean or under heavy load

since premium burns slower it burns a little cooler, make sense
 

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Posted by hidnn.o.s. (Member # 1219) on :
 
You are more knowledgeable than I on the subject. Goodluck!
 

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Posted by 66 AC COBRA (Member # 904) on :
 

quote:

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Originally posted by hidnn.o.s.:
You are more knowledgeable than I on the subject. Goodluck!

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no, i just like to over rationalize things to make them more complicated and therefore never work

i should have drove the thing off a cliff today, i wonder if the insurance company would be suspicious
 

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Posted by Hungry Hippo (Member # 537) on :
 
i say the egr is clogged or went bad. but i'm just a hippo, i cant even own a car

also, was the cat a quality replacement?
 

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Posted by 92coupe (Member # 1957) on :
 
NOx is made at 2,500F degrees in the CC, just because the cats are new doesnt mean they arent bad. ALL cats now have a NOx bed in them right before the actual catalyst, the bed is designed to cool the NOx down. make sure the car isnt running lean, even try fatting it up just a little. depending on how much time you have a have an actual book from one of my ASE courses, if youwould like i can scan through it and see if i can find anything to help you out. PM me and let me know if you want me too.

Justin
 

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Posted by BCINGUU (Member # 2397) on :
 
Most of the smog equipment on the vehicle (EGR, air pump, etc.) are designed to put NOX back in the chamber for reburning. Check or replace the EGR and check the air pump.

If you were running rich or lean, your HC would be high.
 

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Posted by Joooestang66 (Member # 2828) on :
 
dont forget to overinflate the tires (if you live in an enhanced area).
 

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Posted by 66 AC COBRA (Member # 904) on :
 
well if it was a mustang cleaning the egr and checking the air pump would be easy

BUT this pos jeep doesnt not have an egr valve, does not have a smog pump, and does appear to have a bad cat

the cat was replaced and sas replaced with a piece of shit cat from who knows where, it is so far down stream i would be surprised if it every got hot enough to work right

so i am putting a new cat on, f**k its expensive for a good one
 

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Posted by Don (Member # 938) on :
 
Timming??????? Just a thought
 

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Posted by Hungry Hippo (Member # 537) on :
 
just add another cat closer to the manifold

[ August 30, 2005, 12:03 AM: Message edited by: Hungry Hippo ]
 

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Posted by 66 AC COBRA (Member # 904) on :
 

quote:

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Originally posted by Hungry Hippo:
just add another cat closer to the manifold

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thats what im going to do homie
 

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Posted by Hungry Hippo (Member # 537) on :
 
thats gonna be clean yo! running clean, that is
 

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Posted by Jimbo (Member # 1456) on :
 
Hang on, before you go adding cats and stuff like that. Check to make sure fuel pressure is in spec, a clogged fuel filter can cause a lean condition. Also, might want to make sure they had the cooling fan blowing on the front of the Jeep during the test(if outside air temp was over 72 deg during the test they are REQUIRED to have it on). On the printout, check the CO and espically O2 levels, if they are at or near zero the cat is probably fine and you should look elsewhere. If they are higher than that it COULD mean the cat is bad but it could also mean the cat wasnt hot enough during testing. Hope this helps.
 

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Posted by 66 AC COBRA (Member # 904) on :
 
well i put on a nox buster cat, didnt help
timing is spot on, fuel pressure is fine

the only left to do is replace the O2 sensor, run ome sea foam thorugh it to clean the carbon out of the cylinder (lower compression a little)

and thats it, after that the motor is junk, time to roll the fucker off a cliff
 

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Posted by rickm237 (Member # 5323) on :
 
put a quart of ATF in the tank then fill it up-you'll pass almost 100%
 

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Posted by 66 AC COBRA (Member # 904) on :
 

quote:

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Originally posted by rickm237:
put a quart of ATF in the tank then fill it up-you'll pass almost 100%

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quote:

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Originally posted by 66 AC COBRA:

quote:

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Originally posted by rickm237:
put a quart of ATF in the tank then fill it up-you'll pass almost 100%

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this sounds very similar to what sea foam does, cleans the engine out and smokes like crazy for a while

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When i worked at Speedee Oil Change way back when....we used to have a kit that included fuel inj cleaner and some stuff we used via vaccum to clean out the combustion chamber kinda like what you guys were talking about....that and a tune helped a large % of the cars that were borderline.

Then again there were no load based dyno smogs back then

Also some stuff called "clean power" helped some borderline cars as well. It was an additive to the fuel system.
 

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