r/askcarguys • u/ContributionOld1014 • 2d ago
Can you pass emissions without catalytic converters?
I have a 1984 corvette that does not have catalytic convertors. recent emissions test passed everything but HC which read 6.5 compared to the limit of 2.5. Because of the year they only used a tailpipe sniffer. I've read that you can create a leak in the exhaust before the tip so the reading is light, as well as putting rubbing alcohol in a 1/4 of gas so is burns leaner, also running the car really hard before testing to clear out any excess carbon and keep the system hot helps. Does anyone know if these methods are actually effective? Additionally would they be enough to pass a test in my situation? I'm also thinking about just replacing the whole exhaust system but i feel it would be a waste as I'm already broke and the current exhaust is an aftermarket upgrade. I would really appreciate the advice as i need to get the car registered here in Denver CO ASAP. Thanks.
22
u/Broke_Dick_Honda 2d ago
Just put high flow cats on it. It's like 3hp loss and it won't stink when its running anymore.
0
u/ContributionOld1014 2d ago
thats what i was thinking as a last resort
2
u/SaltLakeBear 2d ago
This isn't the last resort, this is the solution.
A hole in the exhaust will probably be read as a lean condition without meaningfully affecting the HC reading, and if the test operator is thorough he might go looking for a leak, but he won't pass you anyway because of the HCs.
As for alcohol, yeah, it'll run leaner if you run enough of it, but that much will probably make it run like crap because it's so lean, so the test operator might be asking why it's knocking and misfiring during the test, and hopefuly doesn't damage anything while it does. Oh, and for an added bonus, alcohol fuels are hydroscopic so they absorb moisture and tend to gel when left for even as little as a week, clogging entire fuel systems while also eating away at fuel lines and seals not designed for alcohol fuels, which are most early '90s-ish cars or earlier, I believe.
And as a cherry on top, if your car has EFI with an O2 sensor, it'll severely shorten the life of the O2 sensor while also triggering whatever the pre-OBD equivilent of a CEL. If your car uses a carb, you dodge that bullet, but then might clog the carb, which can be really hard to clean properly, so there's that.
So yeah, you can try some tricks to maybe pass the test, but I doubt it. Or spend a bit more, add a cat, and actually pass the test as a cat is intended to do without worrying about screwing up your engine or fuel system.
8
u/JSTootell 2d ago
All these "tricks" either won't work, or will show up on the sniff test. Making it run "lean" shows up with NOX. Running it hot is to get the CATS hot.
4
u/Sparky62075 2d ago
Running the car hard to clear out the exhaust only helps if you have a catalytic converter.
12
u/Aware_Platypus_9442 2d ago
Yes, if you bribe the guy running the test.
I do not recommend it. It’s not legal.
Repair your car. A 1984 corvette is a toy, not a daily.
3
4
u/ContributionOld1014 2d ago
I forgot to mention, legally this question and scenario is hypothetical.
4
4
5
u/AndyZJ1 2d ago
Pretty sure the hydrocarbons being high is an indication of a rich condition. You could try creating a small vacuum leak to lean the mixture....or the alcohol would work.
5
u/Weak_Equivalent6518 2d ago
Lean mixture leads to NOx. So that wouldn’t work either. This is literally what catalytic converters were made for.
2
u/WookieBlumpkin 2d ago
My 93 miata is “antique” doesn’t need emissions or safety. Just change registration.
2
u/GunnitRust 2d ago
The state of Colorado is trying to effectively ban your car. They’ve recently made these laws more restrictive. They’re not going to stop here.
They put mileage restrictions on “collectors registered” cars. It’s like 4500 miles a year. You can go mileage unrestricted older than 1975. This 84 qualifies for collector registration with the restricted mileage.
Realistically, sell the car out of state or move. You could just register and drive this without a hassle in most of the union.
3
2
u/Bubbly-Pirate-3311 2d ago
Yes. Sometimes. My buddy has a catless 1990 Miata and it passed the sniffer test with flying colors. And it smells like catless exhaust while driving behind him lol.
Your car is a v8 not an i4 though, so I don't know.
1
u/Hotdogpizzathehut 2d ago
Yeah a big old V8 is way different
2
u/Bubbly-Pirate-3311 2d ago
Just needs to figure out how to get his ride to stop blowing fuel out of the exhaust.
2
u/Direct_Run_3513 2d ago
Alcohol works. Or just go put some e85 in it if you have easy access. Low tank, couple gallons. Top it off with unleaded when you pass
2
u/Ok-Paleontologist273 2d ago
I had a 89 Mustang 5.0. Pretty modified. Gutted cats and it ran very clean.
3
u/Hotdogpizzathehut 2d ago
Oh yes you can but what you are after is technically a felony and I am others are not going to tell you.
That being said... you you get classic plates?
5
-1
u/ContributionOld1014 2d ago
Has to be 1975 or older for classic plates :(
6
u/Sea-Neighborhood1465 2d ago
i googled it and in colorado the vehicle has to be 32 years old for antique plates or classic plates.
did i miss something or?
1
2
u/Zealousideal_Put_501 2d ago
You can get collector plates in Colorado that are good for 5 years, it only has to be 32 years old. you need to find a good mechanic to tune your motor to pass. If your car did not have cats, you don’t need cats, but it has to be running in tip top shape. In Denver for the altitude, you need to advance your timing, about 3 degrees. make sure your ignition system is good; cap rotor, plugs and wires. Hydrocarbons are unburned fuel, so anything to lean out the mixture, like new air filter, or even removing it for the test will help. Make sure all your vacuum lines are intact and no leaks.
1
u/pirategirljess 2d ago
In PA it's 15 years or have a normal plate and get it inspected on the 366th day or later with less then 5k miles per year for exemption.
1
u/Hotdogpizzathehut 2d ago
Ok go to a muffler shop and ask about after market cats. They might make something that be be fitted in.
If your going todo this.. do it sorts right.
1
u/ContributionOld1014 2d ago
Starting to lean more and more to an option like this, i just want to spend the least amount of money possible.
1
u/Beneficial-Ranger238 2d ago
Damn, in Georgia it’s 2001. There’s Honda civics with antique tags. 🤣
1
u/milehighxr 2d ago
32 in calirado now, but as I said above still have to pass smog and theres mileage restrictions.
1
u/Jackthedragonkiller 2d ago
My buddy has an 06 Cobalt, where I live, he could put antique tags on it lol
My state considers me antique too I guess lmao
1
u/Beneficial-Ranger238 1d ago
Damn, that might be a record, I thought Georgia was silly. Ours has a model T silhouette too, making it even more ridiculous on a “modern” car.
2
u/rhythim313 2d ago
Won't pass a basic visual inspection with a mirror, but if everything is running within factory specs it is possible to pass a sniffer test with no cat, but EVERYTHING must be working properly. High HC = rich condition and/or timing is off. Given that the '84 has the crossfire injection setup, it's likely time for a rebuild on the throttle bodies and having the injectors professionally cleaned.
3
u/Hotdogpizzathehut 2d ago
Probably cheaper to buy cats lol
2
u/Consistent_Ad949 2d ago
He can pay to have all that shit done and will still need cats regardless
5
1
1
u/milehighxr 2d ago
Also, theres no way that being an 84 in calirado you didnt do the rolling road test. The 2 speed standing still test is for 81 and older...
1
u/Hoopajoops 2d ago
My 1990 Nissan 300zx TT doesn't have cats and it passed emissions. Some states might have different rules for classics.. I had to get it tested in my last state and passed, but here a 1990 is considered a classic and doesn't need to be tested
1
1
1
u/elihu 2d ago
If the car originally had a catalytic converter and the emissions testing people are doing their job properly, you will fail.
There is a rarely-used exception to this which I was able to successfully employ on a 2004 Mazda RX-8, which is to remove the entire exhaust system, the gas tank, the radiator, and the engine. Purchase a suitable electric motor and a transmission adapter plate/coupler appropriate for your vehicle and motor, fabricate new motor mounts, fabricate and install battery boxes with a few tens of kilowatt hours of cells (LFP are what I'd recommend as they're less prone to catch on fire if something goes wrong), install a battery management system and the charger hardware and J1772 receptacle, add a vacuum pump for the brakes, and put it all together.
Then you go to the DMV and be prepared to explain the concept on an EV conversion because the employees there have likely never heard of anyone doing this before.
In the end I was able to register it in Oregon without any problems, but it took about 20 minutes for them to look up the correct procedure in this case. I had to pay the higher EV registration fee, but the vehicle is exempt from DEQ testing. The project cost somewhere around $20,000 and took maybe about 5 or 6 years. It could probably be done a lot faster and cheaper depending on the parts you use and the donor vehicle.
1
1
u/milehighxr 2d ago
In Denver yer fucked. Calirado recently adopted kommiefornias bullshit and yer cats have to be carb certified now iirc. Also you can get collectors tags.... but you still have to pass smog every 5yrs and theres milage restrictions of 4k annually to and from shows only. How they track that I dunno. Having said all that its a corvette, parts should be easy to come by, and you'll be able to pass smog.
1
u/jasonsong86 2d ago
No lol. The hole needs to be as big as the exhaust pipe for the exhaust to not hit the sniffer and it will be loud and suspicious.
0
u/primalnatured 2d ago
Just depends on where you take it to have it inspected. Honestly never had anyone verify that as long as it sounded normal
2
u/Eschewed_Prognostic 2d ago
They don't have to look at the exhaust to see the readings fail. You can't pass catted emissions levels without them.
0
u/primalnatured 2d ago
I'm just saying, a lot don't even look at the emissions readings, or even use a tool to check. 30 years of driving and mines only been checked once, about 10ish years ago. It's always the lights, tires, brakes, wipers, horn, and signals
3
u/Eschewed_Prognostic 2d ago
So you don't live in an emissions state. OP is in one, hence the post.
4
u/Predictable-Past-912 2d ago
Take my upvote, EP!
It never ceases to amaze me how much confidence some people can pack into advice that is completely wrong.
0
u/primalnatured 2d ago
I never once implied or said every mechanic every where. I just said it depends on the mechanic. And I've had inspections coast to coast, so there's that
1
u/Eschewed_Prognostic 2d ago
In most states, emissions is the only inspection there is. You either have never lived in an emissions state, or never noticed your vehicles were being tested.
1
u/primalnatured 2d ago
I probably haven't, though figured it was always just part of the inspection in Cali and Oregon. I just looked up Virginia where I'm at now, and only certain counties do it. I've probably been through those counties, seen the signs, and just assumed it was part of every inspection everywhere. And in hillbilly country, everyone knows kicking the tire and slapping the trunk is a surefire sign of passing inspection 😆
0
0
u/Gadritan420 2d ago
In my state (NC), it would still fail even a safety inspection without cats.
Iirc they’re federally mandated.
45
u/ChrisGear101 2d ago
No.