As the title says I failed the darn dyno emissions test, last year w/ the addition of my Catco cat I passed easily, now I'm back to failing.

It failed on HC and CO. I de-tuned the carb some to run leaner and retested and it dropped to HC just barely passing, w/ CO down from 4 times the limit to just shy of 2. So only CO failing now. Tried dropping jets down again to run leaner still but the test numbers went back up.

Through all this I left the timing alone. I think I'll go back to the jets that let me nearly pass and play w/ the timing. I am running approx 8-10 degrees initial timing, I'm assuming retarding the timing would lower emissions correct? Any other ideas for tuning? Stinking emission *****...

So my main question for all this is will retarding the timing from the current 10 degrees advanced help at all, I adjusted it to about 6 degrees just now, and will put in some heavy advance springs to make sure I don't get any centrifigal advance as well (unless someone thinks that would be worse for emissions) before I take it back to retest tomorrow. This is the last free check I get without repaying so I really need to pass this time...

I was thinking perhaps my cat is clogged up or something, but I'm hoping that's not the case (only been a year or so since new Catco). Hopefully I can de-tune this sucker enough to pass the test, and then re-tune it after the test back to gross polluter status, lol...

Oh yeah, I think I'll go ahead and change the sparks plugs in case they're fouled. Although they're not that old and weren't fouled last I checked. Assuming they are slightly fouled would that even impact CO at all or is that the wrong area to concentrate on?

Thanks for any help ahead of time.

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

[This message has been edited by Ray87Z (edited March 20, 2001).]

 

Ray,

The high hydrocarbons and monoxide numbers still indicate a rich condition. Retarding the timing won't make the situation any better, but worse. If anything, advancing the timing to the point of detonation should clean up the CO because of more complete combustion.

You need to get the combustion temperatures up a little and get more air injection to the cat instead of dumping it from the diverter valve. A hotter thermostat might help, or holding off the cooling fans a bit could get the temperature up enough to help get you through the lanes.

I think that retarding the timing and killing the centrifugal advance would not help your numbers at all.

You might also consider lower octane fuel with alcohol additives, since the CO is replaced by CO² in the combustion process, and the alcohol burns a little cooler than gasoline. This should work well with your advanced timing to help complete the combustion before the gasses get to the cat.

And make sure the engine and cats are really warm before entering the test lanes.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

Hmm, I don't think it's still rich, because the numbers went back up when I tried running even smaller jets for the third test (best numbers w/ 67 jets, 69s originally, 65s gave higher test numbers than the 67s).

I don't have any air system on the car, no smog pump etc, in fact no emissions equipment anywhere on the car except for the catco 3" cat. (might be why my cat is screwed again if indeed it is bad). But the car passed last year w/ this setup so I'm confident if anything a new cat can fix it. I just want to avoid buying another one if possible.

So retarding the timing won't help huh. Darn, I'll advance it back up I guess. Sounds like I should try advancing it even more, up to 12 or so degrees?

What do you think about changing the plugs, is it a waste of time/money for lowering CO ?(HC passed w/ the 67 jets)

By running alcohol do you mean the emissions additive stuff that claims lower emissions? Can that cut the CO down by half? (limit is 1.00, was at 1.95 w/ the 67 jets)

The engine temp for all tests was 160 degrees on the guage. My fans are wired to run w/ the key, I think I'll try put in a switch so I can run it a bit hotter on the test.

What do you think, will the gas additive junk, slightly advanced timing, and a little more engine temp get my CO down to sub 1.00 levels?

Would creating a temporary exhaust leak aid any in pulling down the numbers? That would get some O2 into the exhaust gas and maybe get some of the bad junk out ahead of the testing sensor wouldn't it?

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

 

yea you could try using autolite "666" instead of the standard "26" im supprised you have passed an emissions test with no smog pump the claim is that the smog pump keeps some chemical out of the converter to make it last longer but no one has a striaghjt answer as to if cats really do what thier suppost to . also you might try about 10 bucks worth of heat. 50/50 gas/heat i heard that works.
im glad i dont have to do smog checks knock on wood.

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85 Camaro RS 350/350 stealth intake, holley street avenger 670
true dual exhaust. "ButtStang killer"
82 firebird 305 all original - the cat and smog crap."All show No go"

 

I did some searches for similar emissions related posts, and a couple people said to run the timing way retarded, and some said to advance it. What's the real deal, anyone know for sure which is better for emissions?

These darn smog ***** have got me all pissed off dangit...

I'm seriously thinking of just drilling a few small holes in the exhaust pipe just after it exists the muffler, before you reach where the sniffer they stick in the tail-pipe would reach. Seems to me this would allow some oxygen in, and smog out before the sniffer can detect it. Am I wrong in thinking that?

------------------
Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

[This message has been edited by Ray87Z (edited March 20, 2001).]