Excessive NOx emissions
 

Here in the lovely state of California, we have a biennial ritual...the smog check. We love this because it helps keep children from having to stop playing because they can no longer breathe. I remember those days...back in the '60s when I was a little kid...not being able to see mountains two miles away...struggling to get a breath.

Took the Oklahoma Rust Bucket in and, wouldn't you know it? It failed. Seems that the NOx emissions are about double the legal limit. Unburned hydrocarbons and carbon monoxide are just fine, however.

Two years ago, I went through the same ritual...so I replaced the EGR, checked vacuum lines going thereto, no joy. Eventually I wound up replacing the cat. Put a good 50k on the car since then. Any good suggestions? Or is it time for another cat? (Too bad I can't stick one of my garage kittens on there!)

BTW, I replaced the EGR because I didn't know (then) that the car had a positive backpressure type EGR.

Check the ignition timing. If it's advanced it will raise Nox. You may have to get another cat. I've found most aftermarket cats don't last as long as the original.

Actually, IIRC, the timing is retarded by three degrees. From a couple years ago...I haven't touched it since...

I once had a problem with high NOx on an old Camry (about 200k). What worked great was an engine treatment that cleaned out the carbon deposits.

It wasn't Seafoam, but it was something similar. I think it was GM Top End cleaner, or something like that. It produces a huge cloud of smoke. Google it.

Solved my NOx problem, and created a noticeable boost in mpg.

Sounds interesting. I've been wondering about carbon in the cylinders...this car has always had a pinging problem...which is why I left the timing retarded. That was one of the little tricks the smog guy suggested to help the car pass the last time...they have a +/- three degree tolerance from spec...and since the car was pinging so much I had to run premium (it still pinged) I just didn't bother advancing my timing again.

You probably realize this is a clue you have carbon buildup.

One of the interesting things about old cars is that power can actually go up, since carbon buildup is increasing compression. But this also obviously causes problems, as you're describing. Anyway, I hope you find a solution. In my case I was very happy with the result.

Put water in a paint gun and spray it in the intake while running the engine at about 2000 rpm.

regards
gary

If you use water, just be moderate with the amount. Excessive water will cause this: https://en.wikipedia.org/wiki/Hydrolock. But that probably won't happen unless you really get carried away.

I once trailered a good customers car 180 miles because he thought the motor was about to throw a rod.

Took a Binks model 7 gun and put a a quart of water in it, set it up for a nice spray pattern and locked the throttle at 2500 RPM. Wire tied the trigger on the gun and let her run that way until all the water in the gun was gone.

It took a while, maybe 10 minutes.

Needless to say my friend was very tickled to know he didn't need an engine. he didn't even mind the tow bill, for 180 miles.

I was almost embarrased to charge him 1 hour labor for diagnosis and the water carbon purge.

His statement was priceless.

"Thats why I drive 180 miles past a thousand repair shops to come here where I know I will be treated fairly. You saved me thousands of dollars for a rebuilt engine, and you could have rebuilt it and I wouldn't have ever known the difference."

He had authorized me to rebuild the engine, in advance.

I found honesty always paid me back many times over.

regards
gary