91_TOYOTA_4x4

took it down to get aircare done and wasted 23 bucks. Engine runs great has no problem running, just wont pass. Here are the stats from the aircare-- (Driving) HC at 160.000 fail, CO at 5.92 fail, NOx at 393.000 pass. (idle) HC at 366 fail, C0 at 4.82 fail. So now im trying to figure out what to do. Just checked air filter and it was dust as hell, so i put in new K&N filter and engine seems to be more responsive. I am not sure if that helped alot or wasnt the prob. Can you guys help me out? im gonna get the truck looked at in the next couple of days too.

bigt

how new is your cat?

scope103

Excuse me for a moment while I chuckle mirthlessly. While I've generally gotten "smogged" here in chilly California for around $70, the usual quoted price is closer to $100.

You are probably running a little too rich (high HC due to unburned fuel, high CO due to not enough oxygen to burn it up). The cat is an issue because you are close; but you would need oxygen for the cat to do anything (that's where the PAIR valve comes in).

You can measure the O2 sensor signal at the diagnostic port by measuring the voltage at Ox1 to ground; it should swing from about 5v to ground 7-10 times in 10 seconds (this is an amplified signal; the sensor itself is about .3v to .9v). If it swings, I would suspect the cat is just not keeping up. If it doesn't swing, it could be a dead O2 sensor, or the sensor could be working fine, telling you that the rest of the engine is running too rich.

Unfortunately, there are lots of reasons for an engine to run too rich. Try to work through them one at a time.

Good luck.

91_TOYOTA_4x4

im not sure how new it is but a few people think its still good. Iv been told by a few people also that the timing can be turned back to make it pass, but how much? The air filter was realy dirty when i went through aircare, didnt think untill after i had gone through, could that make i big difference? cuz i was following my dad in it one day and i noticed when he gave here some black exauhst did come out, and i know dirty filters do this. O and could the injectors be a bit dirty or shot? im think plugs could be but the little 22re runs great so still not sure.

dr-dirt

check your egr plumbing. my old 85 truck had the smog not passing problem, and my egr was plugged solid with carbon.

abecedarian

For the record, the code does not mean that you are going from rich to lean, back to rich... ad infinitum. It means that you are either rich or lean and the ECU wasn't programmed to tell you which. Basically, the O2 tells the ECU you are either rich or lean, and the ECU spends too much time either enriching the mixture or leaning it out... or maybe both.

Now you say you have a header? Is the O2 sensor a single wire or heated? It's theoretically possible (considering the pipes aren't helping each other stay hot) for there to be enough airflow across the exhaust to cool the O2 sensor down and push the readings out of spec.

scuba

Abe I wish I could quote your sig...

abecedarian

Insomnia: it's a way of life.

abecedarian

There. Now quote it.

91_TOYOTA_4x4

i have stock manifold running to the cat, then it has a cherry bomb glasspack and then side exit. I will check about the egr being pluged too. You can hear my truck run on youtube just put in ( 91 toyota running ) its blue std cab 4x4. thanks everyone so far

abecedarian

The EGR should not have any impact on HC and CO when at idle (since it shouldn't operate at idle) so that's likely not a problem, though could be part of the problem when off-idle but you didn't post that result.
If any one injector was leaking enough to cause high HC/CO at idle, you should have a noticible misfire. So, could be the cold start injector leaking and the engine has been tuned to minimize it. Also could be incorrect gaps on the spark plugs, or even valve adjustments or worn rings. Done a compression test?
Lots of things come in to play when dealing with combustion events and emissions.

Flash319

I have always found that if the truck is running good and won't pass, put a new cat on and the readings cut in half. It may only stay like that for a short while but long enough to pass the test.

w0eaj

I just fixed my '94 with the same problem - caused by defective (internally broken!) coolant sensor - there is one that feeds the gauge, another for the computer - computer one was telling the compuker that it was 'cold' and needed to richen the mixture - replace the coolant sensor AND the PCV (it'll be crudded up), and your problem should go away.

TC - Denver