Smog test

My 99 corolla narrowly passed smog test recently. Unless something is done, it will not pass smog test 2 years from now. Test result changes a lot in the last 2 tests @ 15 mph


2008 36 0.21 26

2010 63 0.12 259

Car otherwise runs smoothly, no check engine light, although consume oil, half a quart per 500 miles at worst. Can see black soots near the rear bumper.

Any suggestion what I can do to fix this problem before next smog test? or should I begin saving for a newer car?

More than likely it’s the oil burn that’s driving the numbers up but they’re not high enough to worry about from a smog standpoint, move somewhere they don’t have those worthless tailpipe tests. If you don’t want to move, you’ll probably need a full tune-up in addition to valve guide seals and/or rings. Not a bad job but do the whole upper engine if you’re going in there and it wouldn’t hurt to lap the valves as long as you have it opened up. Toyota engines are pretty sound and don’t normally suffer from the common issues like valve seat/head cracks. Probably need to have the cat converter cleaned and the O2 sensor clean/replaced. Check the laws in your state, chances are that the vehicle mfg is responsible for emissions components which means you’d only be paying the labor and not the parts on some replacements. Most important, once repairs are made, the computer must be completely reset. Run a few bottles of Lucas or Redline injector cleaner through it with premium gasoline a few weeks prior to being tested again.

It is possible that the catalytic converter was not warmed up sufficiently. If the smog technician started the test too soon after the engine was started the cat would have been too cool to reduce the NOX or oxidize the HC.

When my car is going for a smog test, I drive it 30 minutes on the freeway before I go to the site. Then, if the car is not tested within 10 minutes, I will go out and idle the engine until the cooling fan comes on again. At the last smog station I used the technician idled the engine will he entered the data; did the visual inspection; and checked the timing. By the time the test was run the cooling fan had come on and the NOX numbers were down where they usually are.

If you are stuck in the “Test Only” catagory, you might have a non “test only” station do a pretest on the car, do any repairs necessary, and give you advice.

Hope this helps you.

The only thing I see wacko is oxides of nitrogen (NO sub x) most likely EGR related, I don’t think the move towards lean is so significant, but possible. EGR system diagnosis requires a medium level of competence, not a 'shoot from the hip" type repair.

How many miles? The HC and NO could mean a simple valve stem seal leak plus regular bits from the valve cover seals etc. This car should go 1000 mi per quart or better. Depending on the miles and a ring leakdown test you should be ok. Your problem could be bad injectors, o2 sensors or a catalytic. A smooth running car should eliminate the injectors. A bad o2 sensor could be putting off the mix a bit. A bad cat will put your NO high as in your message.

Without miles the NO could be a bad cat. The numbers really are high compared to the hc. NO is the big gas for the converter. Thats what it is designed for.

Worry about something ELSE for the next two years…Post back when it actually FAILS…