Failed California smog today. Running out of options.

May 12, 2011 11:38 PM

Went to get my smog test done today. I almost passed it. The problem was that my engine is running a TINY bit too rich. There were more hydrocarbons and carbon monoxide coming out of my car's tailpipe than C.A.R.B. would have liked. The guy that was working at the smog test place was nice enough not to red flag my car for not having my pre-cat.

My car is a 2003 Nissan Sentra SE-R Spec V. Currently, it has 120k miles on it. It runs perfectly fine, minus the slightly worn syncros. The first generation of QR25DEs have had a few problems. The screws on the butterfly valves were not torqued down enough, the balance shaft had a tendency of breaking, and the pre-cat would kick up dust and damage the cylinder walls and piston rings. I put loctite on the screws and re-torqued them properly, removed the balance shaft and replaced it with a Jim Wolf Technology Balance Shaft Removal kit, and gutted the pre-cat to prevent further damage to my engine (the slight damage was confirmed by a Nissan-specialized technician, but compression test said everything is still A-OK).

I have no check engine light on, as I have an O2 sensor simulator for the O2 sensors before and after where the precat was supposed to be. As long as I have one catalytic converter, I could pass the test. Or so I thought. Apparently, the main catalytic converter is too far in the back to filter out the excess hydrocarbons and carbon monoxide.

I believe I have three options, unless I'm wrong of course.

1.) Buy the OEM headers with the pre-cat in tact. This is the most expensive route, and I doubt I have enough money for OEM headers.
2.) Weld a catalytic converter in the midpipe. I'm frowning at this option too, as it's custom work. There's also the matter of finding a catalytic converter. I'm not sure if it's still legal to buy catalytic converters separately in California.
3.) I heard that an AFC controller can allow me to change my air-fuel ratio to make my car run leaner. I have never messed around with air-fuel ratios, but I'm willing to learn more about it if it's a viable option.

posted by RaDeuX to travel & transportation (16 answers total)

Shoot, I forgot to add a few details.

This is what the test results were:
HC Max allowed @ 15mph: 60, @25mph: 43. Mine measured 68 and 55 respectively.
For CO, max is 0.53% and 0.51% @ 15mph and 25 mph. Mine came out to be 0.65% and 0.66%.

As for modifications, I have a cold air intake (though I doubt that causes my car to run more rich), a JWT BSR kit (as mentioned), and the gutted pre-cat (also mentioned).
posted by RaDeuX at 11:41 PM on May 12, 2011

I would call around a few cat places and see what they say. Personally I would throw a new fancy cat into it and see if the change is enough to get you passed. If it does not pass, a new cat at 120 is not a bad call anyway and you will still have to eat the cost of the precat.

A good cat shop will know exactly how to do this, a dealership is not a good cat shop.

I needed something a little less complicated but in the same realm as your problem. My shop actually lifted my car and did the work before I walked into the office to find out the cost. You should have seen the manager turn red.
posted by Felex at 12:40 AM on May 13, 2011

This sounds simple but it worked for me. IN similar circumstances (running just a tad too rich to pass CA smog) I did the following:

1. Had the oil changed
2. replaced the air filter.

Went back 2 days later and passed smog - fyi.
posted by Poet_Lariat at 12:53 AM on May 13, 2011 [1 favorite]

@Felex: Yeah, I never really go to the dealership unless I need OEM parts. The thing is, the pre-cat is embedded inside of the OEM headers.

Since my car still only has 120k miles on it, I don't think the main catalytic converter is toast. Not yet, at least.

@Poet_Lariat: Do you replace your oil regularly? I do it every 3000 miles or less. My car has had Mobil 1 full synthetic for its entire life. The K&N air filter was cleaned during my last oil change, so I think it's fine.
posted by RaDeuX at 12:57 AM on May 13, 2011

Re: AFC controllers and similar piggyback systems

The AFC is one of several good aftermarket piggyback tuners that can tweak the air/fuel mixture. These devices work by intercepting the signals from your engine's sensors, modifying them, and then sending them to the ECU. They can work pretty well, especially in a situation like yours where you aren't really asking for all that much change. Some can be quite powerful.

The catch is there's a steep learning curve to tuning your motor with one of these, especially if you have never tuned a motor before. It also really helps to use a wideband oxygen sensor when you are tuning, and also a good OBDII reader + logging software, so you can see what the motor is seeing.

I've used piggyback and standalone systems on a few vehicles, and these can be challenging to tune in general, and much, much harder to tune on the street. X10 for solo. Factor in the learning curve for tuning + the learning curve for using the software or interface, and I've found it to be much better to just pay a professional tuner and get it done right. In my area (SF Bay Ares) there are several good tuning shops that will put your car on their dyno and tune it professionally. I know of a particularly good one in San Jose, but I believe every decent sized city in California has at least one good tuning shop. The place I used ran $185/hr, and it took about an hour. Money well went for what I was doing, but obviously YMMV.

Even without the AFC, a good tuning shop may be able to adjust your existing motor to pass, even if the cat is not 100%. Tuning shops are very performance oriented and they spend most of their tuning time tweaking air/fuel ratios. They are good at this shit. If you have one in your area, I would go in person and talk to a tuner or the owner. Your numbers are close, and it's possible they can make a tweak or two to squeak you by.
posted by mosk at 2:53 AM on May 13, 2011

If it is available in your area I would try this before spending a lot of money;

Run your car almost to empty, and then put two or so gallons of sunoco 100 octane racing fuel in. The higher octane will allow for a much more complete combustion cycle, burning up all of those extra hydrocarbons. I've used this sucessfully on a car that had zero emissions equipment left after I put in a crate motor for years. Using the fuel was the only way I was able to pass. Just a few months ago I had a intermittent check engine light on a different vehicle, an '98 F150. It had a injector that was partially clogged, causing a cylinder misfire. Three gallons of Sunoco 100 cleared it up; 10k miles later and no more CEL.
Just make sure that you don't use too much, as a full tank could mess up your cats. Good Luck.
posted by chosemerveilleux at 3:19 AM on May 13, 2011

Before spending any money on tuning and replacing the cat, I would get a new o2 sensor.
posted by gjc at 4:50 AM on May 13, 2011

"There's also the matter of finding a catalytic converter. I'm not sure if it's still legal to buy catalytic converters separately in California."

They just have to be CARB or 50 state legal. Summit for example has an extensive selection.
posted by Mitheral at 7:49 AM on May 13, 2011

Run your car almost to empty, and then put two or so gallons of sunoco 100 octane racing fuel in. The higher octane will allow for a much more complete combustion cycle, burning up all of those extra hydrocarbons.

Do you have a scientific cite for that? Because it sounds to me like a common misconception of what fuel octane rating means. Higher octane gas is actually more difficult to combust than standard gas (thus allowing higher compression for engines designed to use it) and doesn't contain any more energy or burn any hotter in a standard engine.
posted by dodecapus at 8:12 AM on May 13, 2011

>"Run your car almost to empty, and then put two or so gallons of sunoco 100 octane racing fuel in. The higher octane will allow for a much more complete combustion cycle, burning up all of those extra hydrocarbons."

Do you have a scientific cite for that? Because it sounds to me like a common misconception of what fuel octane rating means. Higher octane gas is actually more difficult to combust than standard gas (thus allowing higher compression for engines designed to use it) and doesn't contain any more energy or burn any hotter in a standard engine.

There isn't any additional energy per se in the higher octane gas, but the more stable fuel may allow your motor's ECU to run more ignition advance, which, in turn, should allow more complete combustion and lower exhaust gas temperatures. On a normally aspirated vehicle with typical compression, such as this one, it's uncertain how much of a difference this will make to your emissions or performance, but on turbocharged or supercharged vehicles the higher octane fuel can be a significant plus. A lot depends on other factors like the condition and placement of your knock sensor, the general tune of your motor, and the responsiveness of your O2 or AFR sensors. Since you are using O2 sensor simulators, your O2 isn't going to provide any useful feedback to the ECU, so it's all on the knock sensor to tell the ECU to advance the ignition. Bottom line: this strategy can't hurt but it may not be good enough to clean your emissions on its own.

Regarding replacement catalytic converters: make sure you use one specifically approved for your vehicle!! The regulation of permitted aftermarket cats in CA has gotten considerably stricter since 2009, and any cat you use needs to be certified by the CARB for use as a replacement on your vehicle. This link to Magnaflow's info page may be helpful.
posted by mosk at 9:06 AM on May 13, 2011

The exempted new aftermarket catalytic converter is installed with all other required catalytic converters (no consolidation of catalytic converters, nor addition of extra catalytic converters is allowed);

It appears my knowledge was out of date and misleading, especially considering one can't even add additional catalytic converters. I wonder if anyone is making cats that look like mufflers.
posted by Mitheral at 11:10 AM on May 13, 2011

@Mitheral: Do you think the smog test people will notice the extra catalytic converter on their diagnostics computer?
posted by RaDeuX at 11:25 AM on May 13, 2011

A visual check of equipment is part of the smog test. Anyone even semi competent is going to notice.
posted by Mitheral at 11:47 AM on May 13, 2011

@Mitheral: If that's the case, I could just weld it into my midpipe. They looked under the hood, but not the car itself.
posted by RaDeuX at 1:56 PM on May 13, 2011

They looked under the hood, but not the car itself.

Are you sure? The guys here in IL had a mirror on a stick that acted like a reverse periscope that they used to look for the cat.
posted by gjc at 4:28 PM on May 13, 2011

You don't want an extra catalytic convertor anyway. They only really work in the location they were designed to be in. If it is too far upstream or downstream, it will get destroyed by the heat or won't work because there isn't enough heat.

Test your A/F ratio or replace the o2 sensor before you spend $500 on a cat...
posted by gjc at 4:32 PM on May 13, 2011