Suggestions for passing smog

[nicebloke]

Well our old lady Leggy, with 215,000 miles, has reached the end of her time with us, replaced with an STI. So it's time to either sell her or donate her.

My decision is going to be influenced by whether she gets through a smog inspection or not. Last time she passed, but with one reading very close to maximum. She consumes a quart of oil every 300 miles, so might be burning a little, perhaps kicking up the hydrocarbon reading.

Question is this: what steps should I take to maximize chances of passing? Would a dose of Engine Restore be worth it? New plugs? Clean the K&N filter? Run her really hard right before the test to get the cat nice and hot?

[All_talk]

If the HCs are up due to oil burn, a fresh oil change might help, I know my old car always take longer to burn off that first quart after a change. Maybe a heavier grade oil like a 20-50 too.

Gary

[vrg3]

Which reading was close to maximum last time? What were the other readings? It would help if we knew what needed to be improved. Please be specific.

But, yes, running the car hard before the test helps because the hot cat works more efficiently. Also, do a tuneup -- new plugs and wires will make for a more complete burn.

If you're having trouble with the numbers at idle but not up higher, bumping up the throttle stop screw sometimes helps with that because it moves the airflow to a different part of the MAF's transfer function. You're not supposed to adjust that screw, but if you mark its position carefully you should be able to get it back.

If your oxygen sensor isn't fairly new, it's probably not helping things. You can get a new 1-wire sensor (which will work great if everything's hot) for very cheap. And then be sure to let the ECU learn to use the new sensor.

[nicebloke]

Just went back to the last test, and the car did great in CO at both engine speeds and in HC at 2500RPM, but read 118ppm in HC at idle, with the max 120. So looks like that's the only reading that I need to worry about. I'm guessing new plugs and a hot cat should take care of that. I'll also do an oil change as suggested.

[vrg3]

Hmm. Yeah, that ought to do it. Doing my little idle speed bumping trick might help too. It sounds like your engine was misfiring some at idle and the cats weren't warm enough to burn the VOCs off.

[nicebloke]

Okay, so it failed. HCs at idle measured 164ppm, max being 120. CO was fine, 0.25% against max of 1.00%. O2 measured 0.7% and CO2 14%, not sure what they indicated since they don't determine pass or fail.

Readings at 2500 rpm were about average.

Any ideas for next steps for home diagnosis? I'm thinking a new cat might be in order.

Beyond that, we can either have our shop try to fix it, sell her "as is" for peanuts in CA, or donate her.

[vrg3]

What did you do before going in for the test?

Yes, a new catalytic converter will probably make a big difference. A modern car with a hot catalytic converter should emit almost no hydrocarbons.

You might be able to get a complete exhaust used off a newer Subaru for cheaper than a new catalytic converter.

[nicebloke]

Before the test I topped up the oil and changed the plugs then took it on a 10 mile freeway run in 3rd and 4th gear before pulling straight up to the smog station where it was immediately tested, no waiting.

[vrg3]

Ah. So the other suggestions (plug wires, oil change, idle speed, oxygen sensor) may help enough to bring the hydrocarbon number down below the limit, but it does sound like your catalytic converter isn't really doing its job.

[ericem]

don't forget the PCV valve! That could be the excessive oil burning issue. Maybe try thicker oil to. Then dump in some seafoam through the pcv valve. My car with 307,000km (like 200k miles) passed with flying colours with 47ppm. Over here the limit is 200ppm.

[internetautomart]

Isopropyl alcohol in the gas.