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Discussion Starter #1
I live in the Houston area and have to have an annual emissions inspection. I have an 89 Seville with a 4.5l engine. My NOX readings have jumped from 506 ppm last year to 2230 ppm this year. I have replaced the EGR valve and the catalitic converter. Neither of these have changed the readings. The man at the inspection station said the internal passages may be blocked. The car seems to be running fine. My mechanic checked the timinig etc and suggested that I get the new catalitic converter. Any comments / suggestions would be greatly appreciated.

Thanks,
 

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Do not replace the converter.
There are other components in the EGR system besides the valve itself.

First of all I hope you are sure that you got the correct valve.
I am confident your parts store asked you for the numbers off the old valve which would include a P or an N stamped on the valve. Those indicate whether or not you have a positive or negative backpressure valve. Mixing them up can cause problems.
Next, the advice you got about the EGR passages being clogged is probably the best. If the passages are plugged then it won't matter whether the valve is working or not.
To check this just let the car run, if you can get your fingers up inside the bottom of the valve, lift up on the diaphragm. The engine should start stumbling and running poorly. If it doesn't it is likely the passages are plugged. Take the necessary steps to clean them out.
If it does stumble you could have a problem with the vacuum solenoid, the vacuum supply hoses, or the ECM control circuit that opens the vacuum valve that operates the EGR valve.

There are plenty more things to check before you go throwing an expensive catalytic converter at your car.
Besides, if your HC and CO are okay, it is unlikely that your converter is going to fix a NOx problem anyway.

Based on what you posted, I'd say you have a basic EGR problem that just needs to be diagnosed properly.
Good luck.
 

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Discussion Starter #3
I'll try lifting up on the diaphram. The EGR valve that I replaced was an after market one, the mechanic put an AC Delco one on but it didn't change anything. What's involved with cleaning out the passages? Can I try some sort of stiff bottle brush?
 

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I haven't spent much time working on the 4.5. I think there might be a lot of helpful ideas on the forum here.
You could do some searching or maybe someone else could help you out.
That engine was being phased out when I started working for Cadillac and I took a 6 year Chevy break after that.
I am confident you can find good advice on cleaning the EGR passage by searching this site.
 
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