I have a third gen RX-7 with the LS1 swap. I took it to a friendly shop yesterday for NJ inspection and failed their sniffer. My HC levels were measured at 180 and needed to be < 125 at a 1250 RPM idle.

My motor has the following mods:
GM Hot Cam
Long Tube Headers w/ dual high flow cats
Cold Air Intake
and, of course, a tune via HP Tuners

Using HP Tuners, what can I try to bring the HC emissions down to pass the sniffer? Note that I do not have to pass any kind of OBD2 connection...

Thanks in advance for your help!
Steve

 

lean it the **** out LOL take HP tuners with you and flash a really really lean tune into it to idle at and then reflash your other tune back in right when you leave.

 

There are probably two things hurting your HC levels.

One, the hotcam has a fairly high overlap. At low RPM
you can expect some intake - exhaust shoot-through
of fuel and badda-bing, hydrocarbons in the pipe. Not
much you can do about that aspect.

Two, proportional fuel dithering swings the mixture from
too lean to too rich, constantly. The cats are supposed
to average it all out but high-flows have more limited
surface area and touch less of the gas. You might want
to cut back on the proportional fuel swing, keep it a
bit tighter about center. This might also help with the
header/O2 effects.

 

Would a lean tune hurt my other two emissions?
NOx measured 527, must be <829
CO measured 0.02, must be <0.62

Would uping the RPM help my HC emissions with the hotcam?

Is there any downside to decreasing the proportional fuel dithering?


Thanks again!!!
Steve

 

i dont think a lean condition can hurt anything... lean means hardly any fuel and lots of air, also a hotter burn. therefore its gonna burn most everything up and have hardly any emissions.

after all.. emissions are exactly what it sounds like... the left over junk that didnt get burned completely when the cylinder fired.

 

I thought I read somewhere less timing might help when combined w/ a leaner mixture.

 

also, will this sniffing be spreading to more states... as i had said in a previous post, but no one replies. i don't mean to hijack or anything, hell send me pm's if ya want about inspections but i would like to know as i'm building a turbo setup and don't really want to have cats on the car (i live in north carolina in case anyone was wondering or if that helps solve the question)

 

his rx7 is probably pre obd2 which is why they are sniffing his...cali uses a similar plug & play but i belive they ADD a sniffer even on those cars. Most of our surrounding states for OBD2 cars use a combination of plug & play + visual & nothing more.

 

PA does both. I had my '99 SS get the sniffer every year when I lived outside of Philly. Must be stricter policies back east since NJ polutes the whole NE already.

 

Gross mixture error either way elevates HC
Lean elevates NOx
Rich elevates CO

Which pair you get, HC+NOx or HC+CO, tells you
what's up.

If only HC is bad that probably implicates the shoot-through
more than mixture. But here the NOx is up too which says it
may be over-lean. That though is a peculiar result for headers.

 

So... since my HC is a little too high and my NOx is almost too high, leaning out may cause me to fail for too high a NOx number. I think this makes sense...

Would increasing my Idle RPM help me pass? (since I'm running a cam w/ an overlap) Is there typically a limit to how high you can run the idle for these tests?

Also, can anyone substantiate the idea that decreasing timing may help? Interesting concept but I'm not sure I understand why this would help....

One last idea; would exhaust heat tape wrapping the pipe between the header collector and the cat (and the high flow cat itself?) help the cat function better and improve the emissions?

Thanks again for all the great ideas and data points!
Steve

 

there ya go...

 

I wasa thnkiing that if you are running a regular closed loop tune, just set stoich to like 15.5 or something leaniner than normal stoich. Just do this for the test then switch back right afterward.