So, I have the mazdatrix true duals exaust... and since its come time for inspection (and I kinda got tired of having my car smell like a lawnmower) I decided to buy 2 bonez blank cats (from rx7.com) and flanges and welded them up to replace the presliencers in the system.

I also split the air feed line into both cats.

So that is all well and good, but I go to the inspection station today to throw it on the sniffer, and the NOx is about 20 percent too high. The other measuerments were all well below the limits:

_____Measured____Limit
NOx_____1260____1006___FAIL
CO_________0_____0.8___PASS
HC________85_____128___PASS

The test is a load test, i belive at 35 mph, but i might be wrong.


As far as the car goes, it has been sitting for about 4 months (maybe a lil more), and is still on that tank of gas, so I figure that MAY account for the problem (althouh I really dont know if it could), regardless tomorow I will siphon off that old gas into another car and fill it up fresh with 87.

Tomorow I will also replace the plugs and check the timing (and maybe dial in a bit of retard to help cool down the combustion chamber to try and reduce the NOx).

I guess this post is for two things... one to discuss how to make the dual exaust legal, and also to figure out why my car is producing so much NOx (as it seems that most people on here have problems with CO and HC being way too high)

Thanks in advance for your input.

 

I don't know much, but I do know that the cats need to be at a high temperature to be efficient. Maybe heatwraping the headers might help and other tricks that are used to pass, like alcohol,,,etc...

Gil

 

yeah, i kinda wanted to leave alchohol to the last resort, as im a lil nervous about putting something other than gasoline in the tank

as far as keeping the exaust hot, i cant imagine it cools down significantly in the 3 or so feet before the cats, i mean maybe the very edges of the flow are a lil cooler, but the bulk of the exaust is likely still quite hot

 

wouldnt high NOx readings mean your running lean or too hot? alcohol would make you burn hotter and would increase NOx emissions, as would heat wrap. I'd say there's another problem other than your exhaust though. check your timing maybe?

 

yeah, thats what i thought... timing is going to be checked in the morning... besides that I guess I will have to run thru the entire emissions system to make sure everything is up to spec....

Has anyone else had high NOx results... and if so, what was the cause?

 

your cats are working, check the timing like you planned and if you can the AFR's, they might be a bit lean.