yota4life6

Hello...

I just failed emissions today...
Can anyone lend some tips regarding my CO and HC readings being too high?

the HC reading was just a tad high, but the CO was double the allowance..

I really dont want to throw parts at it.. Can anyone suggest anything?

thank you in advance.

krisrayner

CO is your fuel mixture. HC is unburned fuel. If your CO is double the allowable...then your reading is probably 2.5%??? If you are truly that rich, then your high HC is coming from being too rich. What engine do you have? California or Federal emissions? Need to make sure that the air injection is working (if equipped). Make sure the O2 sensor isn't pegged lean (0.0V-0.1V with no changes) If it's working even close to what it should be, the O2 reading should be reading more like a solid 1.0V(with the rich mixture you have), possibly reaching lower voltages on a snap throttle. Don't be surprised if you have a bad catalytic converter, after having driven around with an extremely rich mixture for who knows how long. Basically you gotta figure out if actually have too much fuel or if the computer is getting bad signals (thinking it's too lean and then adding too much fuel to compensate).


Almost forgot, basic checks- fuel pressure and make sure theres no fuel leaking out of the pressure regulator and getting sucked through the vacuum hose going to the intake. Vacuum leaks (sounds wierd but I have seen them cause weird readings, not always the lean reading you'd think), and exhaust leaks prior to the O2 sensor.

Any rough running, misfires? When the engine misfires, the unburned air gets pushed passed the O2, giving a faulty momentary lean signal due to the unburned O2.

HTH

abecedarian

isn't that about the same thing? I mean fuel mixture and unburned fuel are related, right?Mostly a meaningless reading without knowing the ECU's fuel trim adjustment.Again, mostly a meaningless reading... the O2 should be oscillating between 0.2 and 0.7 volts (how much between those voltages and whether those voltages are reached is mostly irrelevant, but more important is that it does oscillate) because the ECU doesn't read how rich or lean the O2 is reading but whether the O2 is reading rich or lean. More like a 'duty cycle' type of thing where when the O2 reads rich, the ECU adjusts towards lean and when the O2 reads lean, the ECU adjusts towards rich. Hence the 'trim' adjustment mentioned above- the ECU tries to keep the O2 bouncing 50/50 from rich to lean and if it spends a little more time rich than lean, it adjusts the trim so that the O2 bounces rich/lean 50/50. There is no "O2 reads 10% lean so the ECU adjusts 10% rich" type of thing going on. unburned air? you mean unburned fuel right, and a faulty momentary rich signal since (air doesn't burn but) the fuel that didn't get combusted passes by the sensor?

and sorry, don't have the energy to dissect all of it.

krisrayner

CO is a byproduct of combustion, HC is a usually a byproduct of incomplete combustion, raw unburned fuel. If you have the other readings as well, O2 and CO2, then you can get a direction to start looking.

The idea behind looking at the O2 voltage is to help see if it's even working. If it's reading 1.0V all the time, then it's accurately reflecting the rich mixure. Feedback signals to the computer-OK. If it's dead, 0V, then you have false lean signal to the computer and it's just going to keep adding fuel to want to see the O2 signal come up.

If you have all the gas readings, and there's no air injection and no exhaust leaks, you can find a Lambda Calculator on line and use that to tell just how rich the mixture acutally is, whether or not it has incomplete combustion. THere's lots of good info on Lambda calculators, and they are a great diagnostic tool for smog failures. Here's a link: http://www.smogsite.com/calculators.html#lambda
If your mixture is pretty close to a Lambda of 1.0, then your problem is going to be in how efficiently the engine working. But it's only acurate if there is no extra, unmetered air, entering the exhaust stream (i.e. air injection or exhaust leaks)


I mean unburned air...basically O2. That's all the O2 sensor can read in the exhaust. Too much O2, then lets richen it up. Too little O2, let's take away fuel. A big "gulp" of unburned O2 sends the sensor to read lean, closer to 0 volts. If it happens often enough and misfiring badly enough, it will bias the O2 sensor reading towards the lean side.


HTH. KInda hard to know for sure where to start looking without actually seing the exhaust readings in real time. What state are you in? I'm a smog tech in Cali and know the laws here.