josephf31 wrote:
I *THINK* I may be found the problem; see picture, today I found the air intake bellows has 2 small holes in it right near the throttle body, one pretty good size you can see the white behind the openings.

Can someone confirm that this could very well be the cause of my high HC at idle emissions failure? Maybe even a occasional slight miss at idle? It would be the cause of a vacuum leak, correct?

Hopefully it's something simple like this and not big $ like the cat. Thanks all!

CentralCoaster wrote:
I would NEVER disconnect the battery before a smog test that included idle. Was your idle rock solid rpm? The smog tests here don't care what your average reading is during the test, it only takes one blip above the limit to fail you, so a solid idle is very important. Luckily they got rid of the idle test though.

Your idle CO, while passing, isn't ok either, it should be much lower.

What is your code for?

I've used that "guaranteed to pass" I guess it burns much more cleanly than normal gas. I have no idea what difference it made without doing back to back tests.

I've used seafoam too. I will never again, as I don't feel comfortable risking hydrolock on my car. I probably hydrolocked my LTD with it awhile back and bent a rod, but it was junk anyways.

That hole can't be helping, it's letting unmetered air into your car. Not a whole lot as there isn't much vacuum behind the filter though at idle. But idle is finicky so you want that maf getting everything.

I'd fix that code properly, plug the hole, drive it a few trips to learn the idle, then run the car hard to redline on a few onramps, and smog it hot.

My vette gets excellent mpg after a track day, so I reason that it will help the smog check too.

CentralCoaster wrote:
Hmm. I guess EGR should only affect Nox. But resetting the ECM will affect idle and everything else.

Does your EGR temp switch and circuit work? It should ground only when hot and EGR is flowing.

It can throw a code if its shorted/grounded. Probably also if it doesn't ground out when it's supposed to be flowing, which sounds like your situation. The sole purpose of that switch is to throw codes.

bogus wrote:
Those are all loosely based on CA SMOG tests.

There is a dyno involved, and a low speed test and a marginally higher speed test. 15 and 25mph, IIRC...

Now, there is one thing you are not talking about. The cats. Or, more than likely, the main cat.

Is NJ doing a visual or just a sniff test?

If it's just the sniff, I would replace the front y-pipe with one that has no cats, then, replace the single main cat with a new main cat.

When you get that close with the numbers, the cat is more than likely dead or dying.

Our Cherokee did that last year. It was in good tune, for sure, but it also wasn't passing. Threw on a new magnaflow cat and the numbers crashed down to earth. I mean CRASHED. I don't remember the specifics, but HC's went from failing at 500 or 600 to passing with under 50.

If you have the $$, try to retrofit an LT1 style system. That would allow for dual cats and dual exhaust and will add about 30hp to the thing.

If you buy a cat, get one that meets CA OBDII standards. They are more expensive, but they also last much much longer.

bogus wrote:
that should do it.

The main cats just don't hold up. You are in NJ, they mandate the "CA standard" cat. If so, don't complain about the cost, it's a much better can than the basic replacement. It will last a long time... it has to meet OBDII durability standards. It might be more expensive, but it will 3 or 4 times longer.

josephf31 wrote:
Quote:

bogus wrote:
that should do it.

The main cats just don't hold up. You are in NJ, they mandate the "CA standard" cat. If so, don't complain about the cost, it's a much better can than the basic replacement. It will last a long time... it has to meet OBDII durability standards. It might be more expensive, but it will 3 or 4 times longer.

Maybe it's just me :-) but I'm confused

http://shop.advanceautoparts.com/weba ... teel-magnaflow_22317388-p

Says only not for sale in CA, nothing about NJ. Most other sites list this and other cats (e.g. Catco) as being "49 state legal".

Is this cat not legal in NJ? or is it just not as good?

One more ? do I need to worry about the pre-cats or if I replace only the main should that do the (emissions) trick?

Thanks all!

One more ? do I need to worry about the pre-cats or if I replace only the main should that do the (emissions) trick?

Thanks all!

josephf31 wrote:
Quote:

bogus wrote:
that should do it.

The main cats just don't hold up. You are in NJ, they mandate the "CA standard" cat. If so, don't complain about the cost, it's a much better can than the basic replacement. It will last a long time... it has to meet OBDII durability standards. It might be more expensive, but it will 3 or 4 times longer.

Maybe it's just me :-) but I'm confused

http://shop.advanceautoparts.com/weba ... teel-magnaflow_22317388-p

Says only not for sale in CA, nothing about NJ. Most other sites list this and other cats (e.g. Catco) as being "49 state legal".

Is this cat not legal in NJ? or is it just not as good?

One more ? do I need to worry about the pre-cats or if I replace only the main should that do the (emissions) trick?

Thanks all!

screamin_conure wrote:
Couple of questions...

Did you replace just the main cat, or the pre-cats too?

What kind of shape are your plugs?

How fresh is the gas in your tank?

Matatk wrote:
Also, since ignition problems can cause unburnt fuel problems, have you ever changed the cap and rotor or plug wires?

Matatk wrote:
Is the car running in closed loop? Do you have headers?

josephf31 wrote:
Quote:

Matatk wrote:
Is the car running in closed loop? Do you have headers?

No headers, stock manifolds. Pretty sure it's not in loop how can I tell for sure?

screamin_conure wrote:
Quote:

josephf31 wrote:
Quote:

Matatk wrote:
Is the car running in closed loop? Do you have headers?

No headers, stock manifolds. Pretty sure it's not in loop how can I tell for sure?

The only way to tell if you're going into closed loop is with an OBD1 scan tool. Something like this: http://www.autoxray.com/product_detail.php?pid=94.

Prices for these can vary, and you can find good deals for used ones on eBay. If you do pick one up, since your car is a '91, make sure that it is for OBD1, and that it can read live ECM data.

Otherwise, just about every well equipped repair shop / mechanic will have a scope or scan tool that can tell what's going on with your system as well.

Ron

Matatk wrote:
Quote:

screamin_conure wrote:
Quote:

josephf31 wrote:
Quote:

Matatk wrote:
Is the car running in closed loop? Do you have headers?

No headers, stock manifolds. Pretty sure it's not in loop how can I tell for sure?

The only way to tell if you're going into closed loop is with an OBD1 scan tool. Something like this: http://www.autoxray.com/product_detail.php?pid=94.

Prices for these can vary, and you can find good deals for used ones on eBay. If you do pick one up, since your car is a '91, make sure that it is for OBD1, and that it can read live ECM data.

Otherwise, just about every well equipped repair shop / mechanic will have a scope or scan tool that can tell what's going on with your system as well.

Ron

You can use a paperclip and observe the check engine light on the dash. Instructions are here:

http://forums.corvetteforum.com/c4-te ... cation-91-5-7l-vette.html

It also references the IAT causing running problems. I recommend getting the car scanned with a tech 1, laptop with tuning software, or equivalent scanner so you can see what your sensors are doing.