I bought a 93 vette last summer and it wasnt smogged(I know. Stupid). So I did some of the obvious things that it needed, it had a BBK 52mm throttle body on it. I replaced it with a stock throttle boby. It also had an adjustable fuel pressure regulator, I replaced it with a stock regulator. I have since found out that it has a performance cam in it and roller rockers. It failed smog today at idle CO% 1.12 at 709 rpm. It passed at 2512 rpm at .07 CO%. Does anyone have any ideas to get it to pass. I think it has to do with lift and duration of the valves with the performance cam, it really lopes at idle. The county where I live in cali only makes you smog when you buy and sell, but it would be nice to fix it forever. I am going to try to include a picture of the test sheet.

 

 

Bump

 

Only thing I can tink of - what was the water temps for the idle test?

See if someone can datalog it at idle and see what its trying to do?
Might be able to create an "emissions" chip for it. Its not like you are spewing black smoke at idle

 

I took the car in first thing in the morning 1/2 mile drive, they do the standard 2 min warmup before the test. so it was barely at temp. Ya this is way over my head, do you know if ECM tuning could solve it?

 

Your air/fuel ratio at idle will effect your co. Anything under 14.7:1 will start an upward curve on the co %

 

buy a smog certificate from a "friendly" smog guy. come on this is a no brainer, you have a big cam and you live in smog **** land. cali hates your camshaft and hates your performance mods! hell they hate race tracks... lots of guys here run big cams with lots of performance mods and their cars are 100% "legal".

by the way if your cam is over a certain size it will never and i mean never pass smog in cali

 

Thanks Kimmer I am investigating that also. I dont know how big the cam is, guessing not to extreme. I dont think buying a smog cert is a solution. Learning alot today about this car. I will overcome

 

Your tune may be off, due to the parts change. You may need to do a datalog and retune.

 

Here are a couple of things to try. Make sure the car is good and hot before taking it in for the test. If it has a 160 deg F thermostat, I would change it to a warmer one (180-190 deg F).

USe gasoline that has ethanol in it or if you can find it add "Guaranteed to Pass" (I'm in Canada so not sure if that is available in Cali).

The other thing to do is to bump your idle up to 900+ RPM.

As others have said, the cam may be too big to pass, but it's worth a try.

BTW, we have a '94 with a GM hot cam in it and a custom tune. It passes emissions here...........although next test it will probably need new cats. Close to 200,000 miles on it!

Good luck.

 

I already thought of idle bump up but I'm not sure how to do that. Can that be done with the ECM or physically on the TB? I read about guaranteed to pass but was not sure. The test was real close and the car was real cold so I think I got a chance. Thanks for the help.

 

What is the process for a datalog and retune, is that something a shop has to do? Is that something I can do with instruction, or is it something I can send my ECM for a retune? If I could figure it out I would Like to buy a tuner and do it myself. Knowledge is power.

 

I'd scan it at idle to see what fuel delivery looks like. The high CO means it's rich - really rich actually - and there are simplistic causes/solutions depending on whether it's rich/lean from the O2's. This assumes it's a stock tune - it may not be given the mods. No car needs to be terribly warm to pass a smog test - but that assumes it's still resembles how it came from the Factory. Yours may not.

 

bingo!

You'll need to goto Redding or Sac for a dynotune
MSI in Sac is the best IMHO

 

Well, there's a second vote for MSI

http://forums.corvetteforum.com/c4-s...emissions.html

 

If your "hot cam" is not for CA smog it will never pass. That was the first thing I told Elliot Portworks. "I need to pass CA smog"

Catalyst converters must be at least at 900°F for them to be at operating temperature. If you drove from home to the smog shop, parked there 10-20 minutes awaiting for your turn then they were cold cats. Cold cats on older cars with today's smog demands = fail. 0.12 is not a lot, I've seen way worst than your numbers.

Two years ago I smogged both Vettes. Betty Boop is stock with OEM cats and the Ghost with 383, LE2 cam, heads, port and CA hi-flow cats (new). The Ghost had better SMOG numbers. I wonder if the OEM cats are just too old and its time for them to be replaced.

There is no need for illegal "friendly" smog guys. Posting crap like that on a public forum is a non-smart way to solve a simple problem. You car is already flagged at DMV, once you failed CA smog test it sends a flag to DMV and it will be reported in your carfax. Trust me, I know this. Once Beety Boop had the breather line from the valve cover to the TB loose and they failed me. The guy told me, I walked to the Vette, pushed the line into the TB and I passed. Three years later I got a free carfax report and that was in the carfax.

I dont think you need new catalysts but, just in case

http://www.magnaflow.com/02catalytic...ayproducts.asp

You could research that new cat-clean product and see if they work.

 

Thanks PLRX alot of good info. Is there a way to tell the size of the cam? I am getting ready to do a datamaster datalog, can a tech tell by looking at that whats going on with the cam. Also checking on fuel injector size.

 

Do you know who the PO was or who installed it?

 

No it was like that when I bought it. I would say they were never planning to smog it again

 

first, before a "re tune" or "new tune" may I suggest a "tune up" ? Which at a minimum would include new rotor and rotor cap for the opti, new plug wires, and spark plugs ?

I live in California (and you don't spell it with a "K") My 96 when nice and hot (stock 195 degree thermostat) with a LT4 "Hot Cam" and a good tune up and the stock computer posted the following numbers:

CO at 1293 rpm, max allowed 0.43%, measured 0.19%
CO at 2039 rpm, max allowed 0.46%, measured 0.02%

please note that your 93 is allowed more than twice the max CO as a 96.

An LT4 Hot Cam has .525 / .525 lift and 218 / 228 degrees duration; not the biggest cam by any means, but I have read in this forum of members legitimately passing California smog with much bigger cams.

Allegedly, GM designed the opti spark ignition to be a 100,000 mile maintenance free system . In my own experience, the ignition system on my 96 was SEVERLY degraded, yet the car ran well.

A complete tune up, as any LT owner will tell you isn't easy (or cheap); I would theorize that your 93 may not have received one in quite some time .

Don't be discouraged. You're very, very close to passing smog. Good luck