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CA smog fail 5 times.... running out of ideas

Old 04-29-2019, 04:24 PM
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Default CA smog fail 5 times.... running out of ideas

Hey everyone!


Recently picked up a 93 Jeep Cherokee Country with a 4.0. I failed CA smog on Nox at 15mph and everything else passed with flying colors going in with no knowledge on the vehicles past and the smog tech told me I needed a new o2 sensor. Changed it and came back to fail again on Nox. Since then, I have smogged a total of 4 more times and changed the following parts: o2 sensor, carb legal cat, Coolant Temp Sensor, MAP sensor, map sensor vacuum line, Fuel Filter, Oil, Muffler for back pressure, 165 degree thermostat(will be changing back to 195 thought it could help cool), champion spark plugs, rotor + distributor cap. I also wired the e-fan to a switch and ran it during the test.


To my understanding, the 93 xj does not have an egr.


One of my last ideas would be the charcoal canister. Do you think it could affect Nox? I have not looked too much into it, but its one of the last emissions control devices that i haven't touched.


Here is the Results of the last smog test.






here is some pictures of my engine bay to see if anyone can see anything off about it.














I appreciate all the help in advance ! Thank you!
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Old 04-29-2019, 04:45 PM
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First item of concern is mixture. Which can be observed via the voltage signal generated by the O2 sensor(s). Though a typical multimeter probably won't be sufficient (because it takes periodic samples and averages them). Do you know anyone with a digital oscilloscope? Like a HAM radio hobbyist?

Are those after-market injectors? Has the vehicle ever passed emissions since those were installed?

Have you performed any carbon build-up cleaning?

Has your fuel pressure been tested to ensure that it is within spec both at idle and under load? (I ask because the RPM was similar in both tests, but the 15mph would have been under far less load).
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Old 04-29-2019, 04:52 PM
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Could be a vacuum leak somewhere, but that will have you running rich. Not sure that would bother the NOx reading. What do you know about the condition of your injectors? One of our old timers swears by BK44 as the only injector cleaner that actually works. Wouldn't hurt to give it a shot.



Off topic: That's a pretty clean 93 you have there! By the way, you can lose the heater control valve. Just run 5/8" heater hose and 3/4" *heater hose and cap the vacuum lines, and say goodbye to that troublesome waste of space.



*I don't recall which one is top and which is bottom, but it's easy to tell when you are looking at them.
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Old 04-29-2019, 04:59 PM
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Originally Posted by BlueRidgeMark View Post
Could be a vacuum leak somewhere, but that will have you running rich. Not sure that would bother the NOx reading. What do you know about the condition of your injectors? One of our old timers swears by BK44 as the only injector cleaner that actually works. Wouldn't hurt to give it a shot.



Off topic: That's a pretty clean 93 you have there! By the way, you can lose the heater control valve. Just run 5/8" heater hose and 3/4" *heater hose and cap the vacuum lines, and say goodbye to that troublesome waste of space.



*I don't recall which one is top and which is bottom, but it's easy to tell when you are looking at them.
thank you for the response! The previous owner told me he changed the injectors right before I bought it now sure exactly though!
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Old 04-29-2019, 05:01 PM
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NOX is a sign of high combustion temps. I would suggest using some sea foam in a quarter tank of gas and driving it until almost empty. You might have carbon build up making hot spots inside the combustion chamber
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Old 04-29-2019, 05:40 PM
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Take this post (mine) with a pound of salt - as I have no idea what I am talking about.
But - at some point - maybe 15 years ago - some wizard (in Florida) thought our engine needed these rather thick (thicker than simple foil) aluminum covering the top of the engine, almost wrapping each of the plugs.
It has stayed there since. It must have had something to do with temperature disbursement,
We have never failed an inspection since.
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Old 04-29-2019, 05:52 PM
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My 95 passes CT emission standards without a cat but I get the tank down to a very low level and pour in about 3 bottles of isopropyl alcohol. I dont know how your limits vary from here. After the test I fill the tank and drive it for the next few days till empty. Might be worth a try.
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Old 04-29-2019, 06:46 PM
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Originally Posted by 4.3L XJ View Post
NOX is a sign of high combustion temps. I would suggest using some sea foam in a quarter tank of gas and driving it until almost empty. You might have carbon build up making hot spots inside the combustion chamber
Waterboarding will do a better job of removing carbon deposits.

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Old 04-29-2019, 08:13 PM
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i forgot to mention i have tried to sea foam it twice. The car did not smoke the first time and the second time it smoked for all of 2 seconds.
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Old 04-29-2019, 08:14 PM
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Originally Posted by Cummins93 View Post
My 95 passes CT emission standards without a cat but I get the tank down to a very low level and pour in about 3 bottles of isopropyl alcohol. I dont know how your limits vary from here. After the test I fill the tank and drive it for the next few days till empty. Might be worth a try.
Is that safe lol? What is your states Nox level max?
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Old 04-29-2019, 08:31 PM
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Originally Posted by jordan96xj View Post
First item of concern is mixture. Which can be observed via the voltage signal generated by the O2 sensor(s). Though a typical multimeter probably won't be sufficient (because it takes periodic samples and averages them). Do you know anyone with a digital oscilloscope? Like a HAM radio hobbyist?

Are those after-market injectors? Has the vehicle ever passed emissions since those were installed?

Have you performed any carbon build-up cleaning?

Has your fuel pressure been tested to ensure that it is within spec both at idle and under load? (I ask because the RPM was similar in both tests, but the 15mph would have been under far less load).
I do not know anybody with a digital oscilloscope unfortunately lol. I believe they are aftermarket injectors, the previous owner installed them right before I purchased the Jeep so i don't believe it has passed with them. As far as carbon cleanup, I tried to run seafoam through the throttle body twice, but i did not see much results. I barely got any smoke through the exhaust pipe. I am going to fuel pressure test the rail tomorrow to see if everything is within spec. If it isn't, what would i need to change in order to get it back into spec?

Thank you so much!!
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Old 04-29-2019, 08:54 PM
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Originally Posted by Lancyy View Post
i forgot to mention i have tried to sea foam it twice. The car did not smoke the first time and the second time it smoked for all of 2 seconds.
Did you pour it down the intake after you replaced the cat? That process can knock out a cat. Just putting it in the gas tank is preferable
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Old 04-29-2019, 11:44 PM
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Originally Posted by 4.3L XJ View Post
Did you pour it down the intake after you replaced the cat? That process can knock out a cat. Just putting it in the gas tank is preferable
yes it was after I replaced the cat. The only issue is the car doesn't have a license plate and isn't registered so i'm trying to stay away driving the streets, as I could get in a lot of trouble lol.
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Old 04-30-2019, 03:50 AM
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Is you jeep stock with stock size tires ? because if you have larger tires it will lower your rpm and at 15mph that can lug the engine with the 50% load ,
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Old 04-30-2019, 09:41 AM
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Originally Posted by tech View Post
Is you jeep stock with stock size tires ? because if you have larger tires it will lower your rpm and at 15mph that can lug the engine with the 50% load ,
yes it is stock tire size. All I have currently is a 3.5 inch lift
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