Yesterday, I took the car in for inspection and it failed emmissions miserably. HC - 1.36 (limit is .60)
CO - 13.35 (limit is 10.0)

Should I consider changing O2 sensors?

I plan to further tune the car with LS1EDIT but I did this last year and it passed. I have not done any additional mods this year so something went haywire during hte last 12 months.

Any ideas?

 

Seems I remember you have the same problem around
last year's inspection?

HC and CO point to over-rich idle mixture (HC and NOx
would indicate lean). I figure that if you don't have the
higher-wattage front sensors, with headers in balmy
New York winter weather those O2s are probably doing
as little as possible. Have you tried the 'vette rears yet?
Might consider even applying some wrap, maybe just for
the inspection exercise and then take it off until next
year. I've seen what look like "primary jackets" in Jeg's
that appear to be simpler to put than the tape-wrap.

 

Na... I believe the front sensors installed now are the stock units from the rear. They were used since they have longer wire cables - I think. I have SIMMS for the rear.

So I should order/buy some Vette rear O2s? Any problems with installing them in a F-body with LT headers? Do I need to splice the cables?

I'm not sure what the "wrap" mod is; can you explain?

Thanks...

PS - Last year I failed too. I finally passed after (i) driving 2000 highway miles with mega doses of carb cleaner, (ii) reducing fuel and air tables by 5% with EDIT, and (iii) adding 10 small bottles of dry gas (alcohal-based) to 1/4 tank of gas.

I compared my fail test this year to the fail from last year. This year the HC is way higher.


Does a rich condition destroy the cats?

 

O2s need heat to work. Headers shed that heat more
than the stock exhaust. As O2 sensors age, they get
to needing to be hotter, to work well. Header wrap
will keep more heat in those long tubes. It's probably
a bitch to wrap with the headers on the car but the
"jacket" I saw, looked like it might be easier to do.

Adding methanol to the car will lean it out. Methanol
wants like 7:1 AFR.

Cold O2s appear the same as lean O2s to the PCM,
and it trims accordingly (rich). Additionally, the fuel
swing I think is exacerbated by the O2s being "asleep",
the mixture will not be as tight to center but have larger,
longer excursions and the cats can't "scrub" it to
average when they're long-term-rich or long-term-lean.

With a high overlap cam you are going to have some
fuel shoot-through (elevating HC regardless whether
the mixture is proper or not). But, hitting the proper
null for CO and NOx should at least put you to the
minimum for HC.

Maybe you should go buy a 5-gallon jug of racing
methanol and make a custom once-a-year inspection
tune. Because the HC test only flags, I believe, fractions
that are heavier than methane and methanol will give
you none of those (other than what you get from engine
oil cracking). Hmm....

 

OK; great. This has been helpful.

I'm goning to start with a new set of O2s.... and work from there.

 

I installed some fresh O2s this weekend. The jpb was not too bad using ramps. I had to patch in 12 inches of 22 guage wire to make the replacement passanger side SIMM reach the connector on my LT FLP headers. The old O2s were really black with carbon??? I assume it was running way too rich.

I also replaced the plug wires with MSG 8.5MM.

The car runs better now but I still smell a tad bit of raw fuel from the pipes.

I plan to:

1. Put NOS injector cleaner ($10 a can) in and run it through a tank full of fuel

2. Use LS1Edit to cut the fuel/spark by 5%

3. Put 12 small bottles of dry gas (alcohal based) in a 1/4 tank of gas


I hope it will pass emmissions then....