thisgsx

anyone have any ideas? the only one i know is my timing is off. the mechanic told me it's also probably the cat. anyone?

Sensei

Tagged as a Gross Poluter, sucks. High HC and High Nox.
High HC can be caused by one or more of the following; Incorrect ignition timing, faulty ignition components, lean fuel mixture, aka; lean misfire, defective catalytic converter, bad air injector components. High Nox is typically associated with High HC. High Nox is due to high combustion chamber temps usually related to advanced engine timing or lean fuel mixture.

Check your timing, ignition components, check for air leaks ( vacuum) etc.

Sensei

Check your timing and set to factory specs. Don't try to cheat this, the smog tech "should" be checking the timing. Ask for a manual test or pretest before he links into test mode. You will be able to see the gas readings and know whether you are within limits or not.

thisgsx

damn, this is going to suck. so it is going to look like trial and error from this point on. i just came back from a muffler shop with new cat and muffler. the timing i will tackle it later this evening, when it is cooler out. ignition components i think should be good, i just replaced the ignition switch yesterday, the igniter and coil a few months ago. the only thing i can think of now that is probably failing me is timing.

BMcEL

A malfunctioning EGR can also raise combustion temps resulting in increased NOx formation.

thisgsx

is there anyway to test the EGR?

BMcEL

You didn't say what vehicle this is for. There's a link to some factory service manuals in my signature.

sb5walker

High HC and high Nox are opposite conditions; HC and CO are high when it's running too rich, Nox is high when running too lean (or EGR not working as mentioned). Here are some threads that may be of help:

https://www.yotatech.com/forums/f116.../#post51578357
https://www.yotatech.com/forums/f116/code-25-a-224063/
http://www.motor.com/magazine/pdfs/082009_04.pdf
http://www.motor.com/magazine/pdfs/092009_04.pdf
https://www.yotatech.com/51539693-post60.html

scope103

The catalytic converter has a small effect on NOx, but you're way too high for that. (And why would the mechanic give you free advice anyway?) Also, your CO and HC are right on the money; the classic sign of an EGR failure.

So, yes, look in the manual and run through the tests. One condition they don't discuss in detail (because the manuals are written when the trucks are new) is the tube that injects the exhaust gas into the plenum can get so covered with gunk that it is completely closed. A quick test is to put your hand on that tube where it enters the plenum. Warm is okay, cool means you've got a problem.

The only reason I hesitate is your high o2 reading, which could suggest a very lean condition (which by itself could raise combustion temperatures so high that the EGR can't overcome it.) Since you can't set mixture directly, a truly lean condition will take more effort to diagnose.

Your problem is almost certainly in the EGR circuit. Rule that out before you start replacing stuff at random.

Good luck!

thisgsx

I've checked the tube from the EGR and it is warm to the touch. At this point in time, I may just get rid of her. Im on the fence about it right now. I just came back from a fishing trip to Parker Dam. I live about 190miles away and right when I got to the border of Arizona, my tank was empty. Suffice it to say, I had to pump 3 times making this fishing trip. And with the way things are turning out I may throw in the towel.

john4wd

Move to Indiana!!!! We don't have emission tests, woo hoo no worries here!!!! :}