Dodge Dakota Failing CA Smog


Old 04-27-09, 03:18 PM
Thread Starter
Join Date: Apr 2009
Location: USA
Posts: 3
Question Dodge Dakota Failing CA Smog

I am having a serious time trying to get my beloved 1992 Dodge Dakota Truck to pass the 2009 CA Smog Test. It is failing the NOx portion of the test but passes all else.

The power plant is a 3.9L V6 with a bit over 240K miles. It burns a bit of oil over time but I don't believe excessively. If I punch the accelerator (rarely done) I will get some blue smoke.

It has passed the Smog in time past without the trouble I am currently having. In reviewing past test results, I do note that it has consistently measured above average on the NOx portion.

Prior to taking my truck in this time, I changed oil/oil filter/air filter/spark plugs/distributor cap/distributor rotor. I ensured the PCV valve rattled, added fuel system cleaner to the gas tank, and took her out for a road trip. The next day I topped off the fuel tank, warmed up the engine, and went in for the test. It passed the HC and CO portions of the test but failed the NOx.

After this I replaced the EGR Valve Assy and the O2 Sensor and went back for retest. It failed again with similar results except that the NOx did test a bit lower but still out of spec.

I was told that the EGR system is suspect because the engine does not stumble/stall when EGR valve operation is tested. Actually, it does stumble but only slightly. Nevertheless. I was advised to check the EGR passages for blockage.

I gave up trying to remove the EGR tube when I figured I would only end up busting the fasteners holding the tube to the exhaust manifold. What I did do was remove the EGR Valve assembly and ensure that the Intake/Exhaust ports underneath were clean. I then fired up the engine and I could see/hear/feel the exhaust coming out the Exhaust port. Likewise, I could hear/feel the vacuum running down the Intake port. I sprayed the Intake Port with carb cleaner and noted that the engine will stall if I contine to spray without keeping RPM's up over idle. To me, this is evidence that the EGR passages are clear.

Am I mistaken in assuming that those passages are clear? Will I need to remove the Intake Manifold and EGR tube to properly clean them? Or is the problem elsewhere? The engine does have high mileage but I have regularly changed the oil over the years. The catalytic converter only has 9 months on it so I haven't considered it up to now. But, perhaps it's been damaged somehow. I'm seriously considering replacing it (somewhat out of desperation) based on the recommendation of my muffler shop guy who looked at my test results. He says a bad O2 sensor can cause cat damage.

The 'Check Engine' light is OUT on the dashboard. The 'Maint Reqd' light is ON and has been on for years ever since the original O2 sensor went bad. The engine ran very roughly until I replaced that O2 sensor. The truck has run fine ever since then and passed its Smog (until now) with no problems but the light never went out.

Well, I'm hoping someone can help out with some advice. Thanks!

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Old 04-27-09, 05:47 PM
Unclediezel's Avatar
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
A quick Lesson in NOx 101.

If you have ever had the experience in sweating copper pipe, You know that if the Metal is too hot , the solder doesnt stick, Your lawn mower overheats if it runs too lean, Your fireplace always burns HOTTER, if you Use your bellows and introduce more air.


Excessive NOx is produced when combustion chamber temperatures are too high. First suspect would be a lean mixture.

EGR can very easily be attatched to the scenario, Simply based on the nature of the beast, It introduces unburned gas ( Or at least incompletely Burned) into the intake tract, Thus Richening things up, and cooling them off.

Since the beginnig of time, Dodge has had a problem with The Vacuum transducer on the EGR valve.

Ignition timing ...either adanced or retarded, can also wreak havoc with chamber temps, as can MAP and Coolant temp sensors.

Unfortunately , unless you have access to a gas analyzer, and live data stream from your PCM, there is no easy fix here.. You can easily spend more money throwing parts at ity, than it would cost to let someone properly diagnose and fix it.

Up side to this, If they say its fixed, they are responsible to make sure it is fixed..and passes the smog test.
Old 04-28-09, 09:39 AM
Thread Starter
Join Date: Apr 2009
Location: USA
Posts: 3
Some VERY good tips from a head much cooler than mine! (Pun somewhat intended) Thanks much, I'll be mulling it all over and going thru the factory manual with greater understanding!!
Old 04-29-09, 12:31 PM
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Join Date: Nov 2004
Location: Connectitax
Posts: 456
If you have an out of state friend, could he fake buying it from you and register it in a state with less stingent emissions and give it back to you but registered in his name in the different state? I think that I have heard that California has the strictest emissions anywhere, and heard on CBS evening news a while ago that some town in that state is banning you from smoking cigarettes in your own house. Amazing how cigarette smokers can be treated worse than crack addicts.
Old 04-30-09, 09:19 PM
Thread Starter
Join Date: Apr 2009
Location: USA
Posts: 3
Smile Heaven's No!

Thanks for those tips...but I don't think that would work out all that well for me (as tempting a work-around as it is)!! No, you see, out here in California we are told what we can and cannot do with our private property (home/rentals, fireplaces, cars, cell phones, garbage, used soda bottles, etc.) and what we can and cannot do with our lives (our children, our thoughts, our opinions, ourselves, etc.) and the list grows ever longer. We tow the line here in sunny CA! Thanks, anyway!!

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