Disclaimer: This thread is intended to help individuals having trouble passing smog. It's meant to help you avoid expensive repairs while still keeping your smog emissions within legal limits. Dr_Snooz encourages you to keep your engine stock and in top running conditionÖalways.
I know that our cars are getting older. As they age, they emit more smog. Eventually, the car fails a regular smog check and suddenly the shop opens your wallet and empties it. Or at least it tries to. What will most likely happen is that youíll send the car away to the crusher, shell-shocked by how expensive it all got so quickly. It doesn't seem to matter how well the car was running before. Shops know that failed smog checks are their big meal ticket. You don't know what all those controls do and can't call their bluff. So they quote you something obscenely expensive (valve job, new engine, etc.) and you either pay it, or find a new car.
Some of you want to mod your cars. The smog check frowns on this, so you mod your car and then have an illegal smog check done. This is silly.
A bit of background
It's silly because both you and the smog check are on the same team. A properly running engine will produce fewer bad emissions. Most smog controls are designed not only to reduce emissions, but also to help the engine run better and longer. For instance, the PCV system not only reduces crankcase emissions, it helps to prevent sludge from building up in your block. EGR not only reduces NOx, it helps to prevent pinging. It is in both your and the smog checkís interest to keep these controls working well.
What's more, a typical internal combustion engine runs best within a very narrow fuel mixture range of ~14.7:1. It doesn't matter how much you mod your engine, you still want the fuel mixture being delivered to the combustion chamber to be somewhere around 14.7:1 and you still want that to be burned completely before being blown out the tailpipe. (Forced induction setups, like turbos or superchargers, might require a richer mixture. I donít know much about getting forced induction through smog and suspect the big snag there will be hiding the hardware from the smog tech.)
Theoretically, if you deliver the right fuel mixture to the engine, burn it thoroughly and have all factory emissions controls working properly, you can pass any smog check, no matter how extensively you have modded. Illegal smogs are counterproductive for two reasons. One, they allow you to run a poor tune. This is bad both for the air and your engine. If youíre running too rich, youíre allowing unburned gas to wash down your cylinder walls, dilute your engine oil and hasten the early death of your engine. Not good. If youíre running too lean, you will get preignition misfires and again, the early death of your engine.
Two, illegal smogs allow you to mod like crazy. When your shop gets busted, you are suddenly in a world of hurt, unable to go back and unable to get your car registered.
How to Mod your engine
You are a man, after all. You can't buy a car without wanting to make it go faster. Even if you arenít a speed demon, sometimes you need to replace a stock part, but a replacement is not available or is too expensive. The factory 3g carb is a case in point. It's okay. You can mod your engine without having to resort to illegal smogs. The California Air Resources Board (CARB) maintains a list of California Smog legal modifications. Before you plan any mod, visit the site and see what smog legal options you have. There are quite a few for most cars.
You should use approved parts wherever possible. That isnít always possible though. The good news is that if you buy a non-approved part, you can still pass smog. Itís just more difficult. I feel that it's better to buy a non-approved part and blow clean than to do an illegal smog and blow dirty. Know that if you buy non-approved parts, you have a likelihood of failing smog. You can still pass, but the parts should be pretty incognito.
How the Smog Check works
The smog check has two parts.
1.) Visual inspection - The first part is a visual inspection. In the visual portion of the inspection, the tech will look in your engine bay to ensure that all the factory emissions controls are there and, at least from appearance, still connected and working. The specific components that came on your car are listed on the underhood label. A list of all possible components is available here (http://www.autorepair.ca.gov/80_BARR...quired by law). The tech might also look for non-legal smog parts, but itís not likely he will. Itís even less likely that he will know which parts on your car are not stock, unless you have something really wild, like a green anodized turbo manifold. The tech will also check your timing in this portion of the test.
In most cases, if your mods arenít really drawing attention to themselves, like painted pink neon or the like, then they will not be noticed in the visual portion of the test.
2.) Tailpipe sniffer - The next part is the tailpipe test. California tests for three substances in your emissions, HC, CO and NOx at two speeds, 15 and 25 mph. There are specific allowable limits for each of the gases and if you go over on one, you fail the test. These constituents are inter-related. As you reduce one emission, another will go up. For instance, as you reduce HCs, your NOx will go up. This, obviously, allows for a little wiggle room if you are marginal on one gas. If you are just over on HCs, but fine on NOx, you can lean out your mix slightly, pushing up NOx, getting you through the test. You are shooting for a nice balance of the three. As I said, every engine runs optimally with a 14.7:1 air/fuel ratio. It doesnít really matter what mods you install, you will still be delivering a 14.7:1 AFR to the engine, just more of it and faster.
- HCs are raw unburned gas in the exhaust stream. A carb running too rich or a bad catalytic converter can cause this.
- NOx is what you get when there is too little raw unburned gas in the exhaust stream. Most of the time, high NOx is caused by some malfunction in the EGR system.
- CO is also unburned gas in the exhaust stream, but typically, it comes from sources other than the combustion process, like a dirty crankcase, clogged PCV system or a dirty charcoal canister.
Proper tuning is vital to passing the tailpipe test. Most mods will require some kind of adjustment to work correctly. Sometimes this is as easy as turning a couple screws on a carburetor. Other times it means a few days with a laptop to tune your standalone engine management system. Knowing what to adjust and by how much is the trick to passing smog. The single most important part of passing your smog check is getting the air/fuel ratio right. If you have made modifications that change the AFR, you need to adjust it back so youíre getting a clean burn again. Youíre helping no one by running overly rich.
If you are tuning from a laptop, it should be relatively easy to get the AFR right. If you are dealing with more mechanical controls, then you will have to find another way to monitor your AFR. An AFR meter can be an enormous help in tuning. I bought a narrow-band unit from Edelbrock. It had pretty lights that lit up at various times. That was about it. It didnít really help me dial in the tune. Iíve heard that wide-band sensors are much better, but they are way out of my budget.
A potentially better sensor to use for your AFR is your nose. If your exhaust stinks like gas, youíre rich. Lean it out. When I was tuning my Edelbrock carb, my AFR meter was telling me that I was lean. My nose was telling me that I was rich. I went with my nose and leaned the mix. I passed no problem.
Most importantly, tune to the test. The California smog check tests emissions at 15 and 25 mph. Make sure your AFR is optimal at those speeds, even if itís a little off in other places. For my Edelbrock, I used a combination of the AFR sensor and the feel of the engine to tune. If you know what lean misfire feels like, then you can richen your mixture until it just stops and youíll probably be right. If you donít know what lean misfire feels like, go lean until the engine starts having trouble. Then youíll know.