Cant pass smog due to high NOx

[Leo(209)(707)]

I have a 94 MTX with an after market Y pipe, high flow CA cats, exhaust, and 8lb flywheel. I am failing smog because of high NOx. After my first fail i figured i was running too hot(but far from overheating). So, i replaced my O2 sensors, and flushed my radiator and put in new coolant there. It seemed to run a bit cooler after that. I went back to try and pass smog again. The numbers were better, but still failed for high NOx. Are there any other suggestions for small fixes for this?

The only other thing i can think of is that there is a lot of carbon deposited in the cylinders and that is making it run hotter than it should. My solution would be to clean them by removing the heads and getting in there.

Also i am not going to unplug whatever connector to make it pass smog by making it run ******, and i cant run AutoRX, or whatever its called, because i cant drive it on the road till its registered.

 

[jedhead]

Is the car California model? If so make sure your EGR is working well.

Bob

 

[luigisho]

Pull the SPOUT connector before the test. If that fails then the cats are probably too crappy to make emissions and you might want to buy a good used pipe with oem cats on it.

 

[Leo(209)(707)]

I am trying to pass smog without unplugging SPOUT connector, and the cats are brand new.

How can i tell if it is a California model or not for sure? I don't think it is, because the guy i bought it from brought it over from the east coast, i think. Also do you have any good suggestions on good places to read up on the SHO's EGR system? I don't really know anything about it in general.

 

[luigisho]

Is there a reason you are averse to pulling the connector and potentially passing the test?

 

[raff18]

Run 87 gas it's will lower ur cylinder temps and thus ur nox numbers

 

[rubydist]

CA model mtx cars have egr, non-CA mtx cars have no egr.

high NOx are due to one or more of the following: lean mixture, bad egr, bad cats, bad valve timing.

I had a car fail once due to the cam timing being off - prior owner had not gotten the timing belt on right.

generally, if the egr is bad, you will get a code - do you have any codes?

in my experience, pulling the spout connector will lower NOx by at least one third to one half. I'd do that in a second to pass the test, then worry about why it needed that after I can drive it again.

 

[SHOtimer]

I am trying to pass smog without unplugging SPOUT connector, and the cats are brand new.

How can i tell if it is a California model or not for sure? I don't think it is, because the guy i bought it from brought it over from the east coast, i think. Also do you have any good suggestions on good places to read up on the SHO's EGR system? I don't really know anything about it in general.

Non-Ca MTX cars don't have an EGR system. The EGR system recirculates the exhaust gases and lowers combustion temps - which in turn lowers NOx.

I'd try sucking some Seafoam into the intake and having a smoke show...

Doug

 

[Leo(209)(707)]

Thanks for all the info.

The guy who smoged my car said there was no EGR. So i will try a few tricks and see if i can get it to pass.

The reason i don't want to just pull the spout connector is so i can learn how to fix the problem. I bought this SHO as a project to further my knowledge with cars. It was $400 bucks and there is a lot of knowledge here in the forums to help with the learning experience. Just this problem has taught me many lessons and made me do research. Maybe I'm kind of in nerd in that sense, but i like having my project SHO.

 

[SHOtimer]

I understand completely.

The problem with your car was that it was not manufactured to pass CA smog.

All SHO's that were sold new in Ca had EGR systems. The MTX's sold in all other 49 states did not.

If you had a Ca MTX that didn't pass -that would be much easier to work with.

Doug

 

[walser]

i know some Napa's have a treatment that is "garanteed" to pass emission tests. you could check there. Im not saying it works, never had to used it. But there is stuff for that out there.

 

[itwonder]

You have high-flow non-CA cats and a non-CA car (noEGR). That does not make it likely that it's going to pass CA smog without "help". So, if you want a project, then install an EGR system from a junk CA SHO and replace the Y pipe with a known good factory Y-pipe, and it might pass. Otherwise, pull the spout connector to put the engine in fixed timing mode and pass the test.