Need smog Help

[4RunnerSC]

Long time listener, first time caller.



Went to get brakes and smog done on my 91 runner at a shop yesterday and it failed smog. It failed on the Hydrocarbons and the Carbon Monoxide levels. I figure it must be running a bit rich. They quoted me 130 for a "smog-diagnostic" in which they search around for 2 hours and supposedly find the problem. I left without the diagnosis (since I'd already spend enough money that day) and went home. When they were testing it, my engine was pretty cold (they decided to do brakes first then smog ) so I figured the cat wasn't hot enough to burn that stuff off. I changed the oil and added some emissions cleaner to a new tank of gas. Went to a different smog place today to test my luck. Kept the truck running while in line so it was nice and hot before the test. and guess what, it failed. Now i'm down the price of two unsuccessful smog checks and am weighing my options. After the warm up and the emissions cleaner the results actually did significantly decline for both HC and CO but not quite enough.

Do I go tomorrow and have the diagnostics run? I worry that they will screw me by saying that all sorts of stuff might be broken when really it might just be an O2 sensor or something. Or a more important question: What do I tell them after they quote me a ridiculous amount to fix it?

Thanks in advance

 

[shuly]

I have had a similar issue with an older vehicle that wasn't a Toyota. But you can generally change the O2 sensor yourself cheaply and retest. Because the O2 sensor is in a hot vapor stream it isn't uncommon for it to need replacing after 100k+ (Figuring since you said yours is 91.) The O2 sensor is responsible for ensuring that the amount of oxygen after combustion is correct (w/o going into a chemistry lesson). If it determines that the number is "off" it will recycle the vapor and re-combust the fuel. [I know I am way oversimplifying] If the sensor fails then there isn't any recycle and you end up with CO and excess HC. Your catalytic converter takes care of some of the CO but is primarily responsible for converting the NOx to N2 and O2 (so that shouldn't be the issue). The other common item to fail is the mass air flow sensor. This is a bit more expensive but it measures the air coming into the engine. Generally though, unless your engine is running rough it usually isn't the problem.

Anyway, go get a price on an O2 sensor for your model year (maybe napa auto parts) and grab a wrench. It shouldn't take that long and if it doesn't fix it at least you know of one item that is "new" and the repair shop should not be trying to replace. If they are then you know they are robbing you.