A few months ago in April, my 1984 Corvette was up for new tags. In Oregon, that means a trip to DEQ, the Department of Environmental Quality. They have a pretty slick setup, with my favorite part being a webcam that shows how long the line is . Well, two days and three tries later, the Corvette failed. Barely. For CO the requirement is 1% or less. My results varied from 1.0065% to 1.0001%.

Right now the car is running Chevron Supreme 10W-40 conventional. The oil is pretty old (over a year) and I plan to change it with the same stuff, but is there anything else I should do before retesting? It's not exactly a quick process and I'd like to increase my chances of success as much as possible before heading out there. There are no constant check engine lights (code 42 shows up intermittently, maybe once every couple of months and then disappears on the next start) and I drive the car for about 20 minutes on the highway (55+ mph) before testing.
I've heard the a new catalytic converter can sometimes help, but is often replaced extraneously so I'd like to be sure before I take that step.

 

If you are that close to passing, there are products that you can add to the gas tank that supposedly will make a difference. They "guarantee" a pass for whatever that is worth. Figuring out the code and a new converter will make a difference.

 

Beat the **** out of it, get it freaking hot. That will usually get it. The other thing you could do is bump the timing up a degree or two too. Little bet of a better burn could do it as well.

I've actually seen the canned stuff make cars worse on emissions so it all depends what the problem is honestly.

 

My California '84 would fail if the CO is over 0.56%. My most recent test results were 0.00%. I do have a fairly new cat. I think you could sleep in the garage with the engine running, and this thing wouldn't hurt you!

What is your ignition advance set to? Recent plugs? Check this out: https://www.smogtips.com/failed-high...onoxide-co.cfm

Why 10W-40 oil? Is the engine on it's last legs?

 

That's a good question. I do not have a good answer. Once upon a time I looked it up and that was the answer I found and now that's what I have in the garage.
It does have 174k miles and leaks a healthy amount (maybe a qt every 500 mi, my data is inconsistent), so I figured at that point having oil is far more important than exactly what kind. Eventually I'll fix the leaks, but first up is passing emissions.
I changed the plugs when I bought the car 2 years ago, so fairly recent. I could not tell you the advance, though I can and will check that. I believe 6 degrees of advance is the right amount?

I'll be sure to warm it up good and nice before testing again

 

Definitely change that oil as old oil is a bad thing when having your emissions tested. If you have 174,000 miles on the original Catalytic maybe it is time for a replacement. How old is the Oxygen sensor? Any time you have a car that runs a bit rich or burns oil through the catalytic they shorten its life. If you replace your catalytic with a modern high flow unit the CO might come down the rest of the way and your car will run better. I replaced mine when it was convenient as I had the exhaust system off the car. I bought one from Summit Racing that fit perfectly and still works to this day. It was less than $200 as I recall.

If your car still has the factory Catalytic converter on it then you should probably replace it. I replaced the exhaust system with a Cat back Chambered Pipes system with a new catalytic and I gained almost 14 HP in my C4. Whether it was from the weight reduction or the freer flowing catalytic I will never know but it sure looks, sounds and runs better after the upgrade. I also have no Drone to deal with in my C4.

This might be the time to try one of the cans of "Guaranteed to Pass" cleaners and see if it works on your car. It is all up to you and your budget, as for me, I would seriously consider the catalytic converter and anything else that would make your emissions cleaner. Starting with a good oil change with some Higher Mileage Oil designed not to drip out of your engine. I use Castrol, Mobil , Royal Purple and Valvoline oils in my vehicles and most make oil specifically for higher mileage engines which hopefully means you burn less of it through your emissions system. These oils do help on vehicles with higher mileage. It might help with your emissions.

Best regards,
Chris

 

Put a couple of gallons of E85 in the tank when it is low (under 1/4) and go get tested on the mix. E85 will burn more lean and help reduce the CO. Then after the test fill it up with premium.

 

That's going to be a no for me. The nearest E85 is an hour away. I'll replace my cat before I do that!

I bought it with 172k and essentially no history. A new O2 sensor sounds like a good idea. New cats aren't as expensive as I thought so that might be on the table as well.

I think I'm going to try the oil I have in the garage, check the timing, get some new gas (my lawn mower will happily drink the old stuff) and see what happens. If I still fail, out comes the cat and while I'm at it, a new cat back. I'll also swap in some high mileage 5w-30 and change the O2 sensor.

Thanks for all the help and suggestions! I'll keep you posted

 

Your code 42 is being set because the ECM has seen an open or short to ground in the EST or bypass circuit. Being it is intermittent, it could indicate that the module is starting to wig out, the connections are bad or the ECM. You will have to troubleshoot that with the 84 GM service manual to find out what's going on with that.

The higher than normal Carbon Monoxide (CO) exceeding maximum limits, can be due to a number of emission failures ranging from inadequate air intake to defective engine sensor. This condition is a "Rich Fuel Condition" none-the-less. Check your air filter, O2 sensor, CAT (if that old, you might want to replace it) Fuel pressure @ 13psi for a stock motor, check for excessive fuel at injectors, dribbling etc... Base timing is 6* stock, but you can set it to 9/10* as long as the motor is happy with that setting. Your oil should be 10W-30 stock, what you decide to put in it is your decision. Good luck

 

Probably not the best idea, but i had great luck with a bottle of "heat".
I would dump a bottle in there with fresh fuel, take it for a drive on the freeway to get it nice and hot right before the test.

In my state, my car is exempt due to age and "limited use" agreement.

 

You could just take a gas can with you and put it in before you go test.

 

ValourUnbound I cant see the final resolution or what worked for ya ?

 

Well, I changed the oil, fixed code 42 (the EST connector was loose or something, I unplugged it, scraped the connections and put it back in, no mode mode 42) and then listed it for sale.
Where I'm at (Portland, OR), DEQ is only required for those on the Oregon side of the river and who live close to Portland. Most of my interest seems to come from the Washington side, who don't have DEQ.

​Since it hasn't sold in over a month, I've considered getting it registered so that I can drive it around again, but I can't even do that since the testing stations are closed for a few more weeks thanks to COVID 19.

So in short, I don't know if I fixed it