What do I tweak to fix my HC and CO emissions?

[Ahraxx]

Hi Guys,

My GT barely failed the state emission test just now. My cruise levels are WAY within normal, but the idle flunked me.

I had my RPM set at 1040 – my HC(PPM) squeaked through 216/220 but the CO% barely failed.

I decided to set my idle lower – set it to 710RPM via the screw and that made me fail both HC and CO by a pretty big margin. Lesson learned - high RPM makes for better results - however, I cannot raise my RPM much more as the state will not test RPM higher than 1100 at idle.

I have the AEM EMS, so I can tweak whatever – do I need to make it leaner or richer at idle to get my CO% down?

[Joel_CA]

I'm not much of a tuner as far as using an AEM- but i am a smog technician here in California- and have adjusted carburetors as a means of getting them to pass smog. Hi CO's indicate a rich mixture- Excessively rich mixture can result in an increase of both HC's and CO's. Try leaning it out a bit. Of course it would help if you had a 4 gas analyzer handy to see the result of your adjustments as you make them...

JJ

[RealMcCoy]

Are you using oxygen sensors for fuel control? Is it in closed loop at an Idle?

Do you have a wideband? If so, what's your A/F ratio at idle?

You need to lean it out to reduce the CO, but without knowing the A/F ratio, or if the cat is working, there's no way to know if doing that will lean it out enough to cause misfires, and send your HC to the moon..

[Ahraxx]

Hi Guys,

I will try to lean the mixture and see what happens.

My car is running MAP without O2 feedback. I do have a wideband O2 sensor (innovative brand), but that is the biggest waste of ~$200 I have ever made - the thing is is a piece of CRAP! It goes out of tune very quickly and I think the only way to use it is to recalibrate before each use (which means digging it out of my downpipe). For daily driving, it is worthless...

[Ahraxx]

Per recommendation I leaned my mixture. That got my CO within limit, but my HC spiked up to 262 (I need 220 or less). Now what?

Original Results @idle:
HC (PPM) 213/220 (pass)
CO (%) 2.46/1.20 (fail)

Today's Results @idle:
HC (PPM) 262/220 (fail)
CO (%) 1.04/1.20 (pass)

I guess I could take the tune a notch up...

[wraith]

bring your idle timing advance down a little so you fire closer to tdc. what is your timing at idle?

[Ahraxx]

It was at 15, I lowered it down to 6 and put my fuel a bit richer but not quite as rich as before.

Last result:

HC (PPM) 210/220 (pass)
CO (%) 2.60/1.20 (fail)

I feel like I am shooting in the dark with someone telling me "high, low, left a bit". I need to see what the heck is going on - there is a shop about 20mi away that charges ~$100/h to tune these EMS systems and they have the tailpipe sniffer there... Problem is, I am completely cat-less, which is why I think I am having this much trouble... My cruise emissions are awesome, just the idle... I just cant get over the fact that I need to drag a 20-pound brick under my car that restricts exaust flow, slows my turbos and robs power (hence uses overall MORE gas) just to pass idle emissions...

[Black_Sunshine]

do u have your egr system installed? egr helps bring down cylinder temps and can drastically cut your HC.

[Erron Spalsbury]

On dino fuel I assume? You should put the cat back on, then you'll pass. I've also seen a number of guys a bit of e85 to a dino gas motor and it helped a lot.