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Discussion Starter #1
Has anyone experienced a failed emissions test based on SLIGHTLY (2.65 PPM) Oxides of Nitrogen? I have replaced the plugs, wires, cap and rotor as well as the Cat Converter and still failed. Tune up was definitely needed although the plugs and wires were not terribly bad. Still failed with the above number (Limit is 2.50 ppm). I have since replaced the O2 sensor, 91,000 miles on original sensor and the EGR solenoid. Plan to use top engine cleaner before the next test. With the positive back pressure EGR valve it is difficult to evaluate the function of the EGR.

Any suggestions will be appreciated.

Thanks, Randy in Annapolis area.
 

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While all those things are good for overall emissions, the EGR is primarily responsible for NOx control.
I'd carefully inspect the EGR system. Diapragm ruptures are common due to the extreme operating conditions that the EGR has to operate under.
Cleaning EGR passages can be extremely beneficial also. They suffer from carbon bulidup which won't allow gases to flow.

Other things than can lead to high NOx are increased compression or temperatures due to carbon buildup in the cylinders, poor engine temperature control such as an inoperative cooling fan or low coolant, or leaking vacuum lines or EGR system control problems.
I recently discovered on a '91 Deville that if the Idle speed control motor nose switch codes set, EGR is disabled.
HTH
 

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NOx is a byproduct of running lean or high EGT....

check to see that your AFR is ok ... maybe fatten it a point or two if you can and try your test again...
 

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Please explain the theory behind that statement.
i thought the premium gas trick was common knowledge...since his car barely failed he should have tried this before doing all those repairs not that it was a bad thing....but i would have just waited till the gas tank was low added a quarter tank of premium and then just drove around for an hour getting on the car and gone back for a retest...the hot exhuast and slower burning gas gives your car a much lower reading and it almost always passes....if it still is right on the line just bump your timing back and it will pass....:want:
 

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... or he could just... I don't know... fix it?
:D
true so true..

but on older cars people go through all the trouble of doing the full spectrum of repairs and still fail the smog test....after that you go to the local dps and get a 2 year waiver if you show them the repairs were made....im just trying to give the man tips on the easiest way to get his car passed.
 

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99 Seville STS, 08 STS4 N* 1SG F55
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I had the same problem and burned through >$600 on the cat and other stuff before I replaced the EGR on my 90 Coupe. After that it passed with flying colors two more times. Not rocket surgery. I'm with Ewill on this one.
 

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I gotcha', I was just having a little fun. Thanks for not taking it too seriously. ;)
 

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I had the same problem and burned through >$600 on the cat and other stuff before I replaced the EGR on my 90 Coupe. After that it passed with flying colors two more times. Not rocket surgery. I'm with Ewill on this one.
see you're almost the exact situation that i was talking about....if you would have known that just $12 in premium and 40 mins would have saved you the $600 in repairs...dont you think that would have been a faster less painful solution, i mean you car needs gas anyways to run so u would be using it anyways... :yup:


smog test are overrated to begin with, but dont fret they will be illegal soon so just maintain.....lol
 

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Discussion Starter #13
Thanks for the support guys. I'm totally open to all suggestions and mainly want to correct whatever is causing the failure. Not being an emissions pro, it may take me a bit of investigating to determine the cause. My '93 LeSabre had the same issue and the Cat was all it took to bump it into the very good NOX range. This Caddy is a different animal. The EGR valve has significant vacuum bypass by design and, yes I did compare it to a new unit which displayed the same vented diaphram characteristic. The system relies on positive exhaust pressure to assist in the EGR opening so I may be looking at the muffler as a culprit. Low mileage FL cars are neat but have there own unique issues as I've discovered. This is my first Caddy and I'm a real adventurist when it comes to hide and seek problems.

Thanks again, Randy
 

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A couple of things you can check quickly....
With the engine running see if you can get a finger or two up inside the bottom of the EGR.
Lift up on the diaphragm. If the engine rpm changes and begins to stumble that means the passages are clear and that part is okay.
If there is no change then they could be plugged.

I don't know much about those older cars, but sometimes the EGR vacuum solenoid is on all the time, except when the engine controller commands EGR, then it turns off.
You can take the vacuum line off the EGR valve and then unplug the solenoid, see if there is vacuum at the valve.
If there is then it is likely that the vacuum lines and solenoid are okay and the valve is the problem.
It is hard to functionally test the valve.
Is this a 4.5 liter?

There might be an output cycling test you could run off the HVAC control and use a test light to see if the ECM is controlling the solenoid properly.
I'd have to do some searching for the book.
Maybe someone else has an FSM?
 

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see you're almost the exact situation that i was talking about....if you would have known that just $12 in premium and 40 mins would have saved you the $600 in repairs...dont you think that would have been a faster less painful solution, i mean you car needs gas anyways to run so u would be using it anyways... :yup:


smog test are overrated to begin with, but dont fret they will be illegal soon so just maintain.....lol
My 90 CDV had this little label on the gas gauge that said: "PREMIUM UNLEADED FUEL ONLY" and it never had less than 93 in it from the first tank after I bought it, including the two or three tanks when it failed emissions.
 
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