I went to get my Car smogged here in California with strict emissions laws but anyways I own a 1991 Pontiac firebird 3.1L
which When I went to try to pass smogged I failed At the 15MPH but passed at 25MPH by .1 of a point in the CO%. Everything else passed but at 15 MPH is failed in the CO result.

CO% (15MPH) CO%(25MPH)
MAX = 0.51 MAX = 0.42
MEAS = 0.71 MEAS = 0.41

It usually passes all emissions test but recently I had to redo the Intake manifold gaskets and it actually ran better. Spark plugs where replaced to aswell as the air filter is clean. It used to sputter and be hard to start but it rolls over first try now. Those old cars need to be drove a bunch so I took it to operating temperature on the freeway for a good 20 mins before i went in and left it running and it still failed. The oil change is about 800 miles before the next 3k change. Was thinking about changed the plugs and re gapping them also getting some fuel cleaners for the injectors/carbon buildup.

Im kind of baffeled as where to proceed to lower these emissions. Anyone have any experience or can give me advice on where to start?

 

I see you have another thread. You said you didn't gap the plugs when you installed them. They're standard ACDelco copper plugs?

If you did not gap the plugs properly when you installed them it will affect how fuel is burnt, and thus, affect emissions.

You're so close, it could very well be that simple for you.

Other than that, O2 sensor and PCV valve can be checked. They affect CO

Check EGR operation and make sure passage ways to it are clean. Not sure about V6 but I know on my TPI they can get clogged and sooty.

 

They where NGK spark plugs that where already pre gapped. Even the guy at the smog shop mentioned the plugs so That very well maybe the culprit... or the o2 sensor like you mentioned.

 

If you got NGK Iridium plugs then they should have been pre-gapped, so you don't want to mess with them.

If the o2 sensor hasn't been swapped I'd go ahead and do that. It's cheap and fairly easy. Do the PCV too, again, super cheap and easy.

 

You're so close that even changing your oil could make the difference; dirty oil contains a lot of hydrocarbons and can effect the readings at low rpms.

 

Went down to the store and got a new o2sensor and replaced(bitch to get off) also picked up some spark plugs which the recommend gap for the ones i installed before where pre gapped to .35. the new ones i got where supposed to bet at .45 according to the make of my car which explains the rich mixture not igniting from the smaller gapped plugs hence increasing CO emissions.

Am I on to something here. othe rthan that the oil change like below i will do aswell and then fill with premium gas and take it back to resmog and hope it passes. If it dosent im all out of ideas guys.

 

Changing the plugs is not a bad idea. Checking the gaps on every plug is also not a bad idea. Due to handling (mishandling) the the gaps can be changed, even though they were set at the factory and supposedly protected by the NGK cardboard tube. One bump on the parts counter and the gaps could be shrunken. It's very easy to verify the gaps, and almost lazy not to. Plugs gapped at 0.035 are designed to fire on the ignition system installed in the car. It takes more energy to fire across a gap of 0.045.

The PCV valve could be an issue, but having some intimate knowledge of how PCV pintles and springs are calibrated, I'd suggest cleaning the original valve instead of replacing it with a current aftermarket part.

Premium fuel may not be any help at all, and may be worse for testing. Premium fuel burns more slowly. Think about the ramifications of that. If you can add ethanol it should help lower the CO levels. Even a blend of E22 might get you through the lane. Since it burns cooler, it should help reduce NOX as well.

Moreover, while these are all good suggestions, no one has mentioned the timing. Is the initial (base) timing set at specification, or perhaps a couple degrees advanced? Is the EST functioning?

 

Heres what i went through
https://www.thirdgen.org/forums/tech...emissions.html

 

Cali test checks timing, if its out beyond 2 degrees it's an instant fail. Will note it as the fail reason.

They're mean.

 

It's Kalifornistan - They should be easy to fool. Jerry has been doing it forever.

They have no easy way of knowing whether the balancer has slipped and the tape wasn't installed to "correct" for a slipped balancer damper. That might be a good thing to check anyway. For about a buck from your parts store you can tape a timing strip around the balancer wherever you want it.