[AaronMartinSole]

Found this on another forum:

Quote:
Originally Posted by silverunner99
Hello MTL_4runner,
I have few questions for you (or anybody else that would like to answer):

re. #1) What's an A/F sensor?
re. #2) For the MAF sensor, shouldn't I use the electrical cleaner instead?
re. #4) How would I check vacuum leak?

Thanks!
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an A/F sensor is just like an O2 sensor, but it is electrically different and
sends different voltage to the ECU from in front of the cat. California emissions have them, federal just have 02
it costs about double what an o2 sesor costs. stealership sold me one the ohter day for 217 and the
o2 sensor is 140.

so if you have a California emissions, it is an A/F sensor. definitely not interchangeable with an O2 sensor.

a lot of people have a bad A/F, install an o2 sensor by mistake, and reset the ecu. the car will run wicked
awesome for about 1/2 or a full tank, as the ECU gets a good heater reading from the o2, and thinks
the engine is rich. short term trim and long term default trim fights and runs the engine wicked crisp and
wicked lean, giving you amazing mileage...for a short time. the amazing mileage comes with a huge emissions
penalty of high nox... [as you hear your cats crackle and pop from the higher heat as it burns off any carbon
from the previous problem of a bad sensor and rich condition. you just cleaned up your cats a bit...]

then the computer finally decides the signal pattern is bogus, switches to cripple mode and runs you
rich, putting you back to square one.

anyhow....A/F is air fuel and it gives the ECU a more exact ratio of oxygen, whereas an O2 sensor just tells
the ECU you are either rich or lean, no inbetween. california ECU is programmed to use A/F signals, [but can handle
the signals from a mistakenly installed o2 for a short while, it treats it like rich, then broken.]
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What's very interesting is my car definitely has that raindrops on tin, crinkling noise after shutting off the engine, quite a lot. I'm still reading and trying to comprehend this. This post was also educational:

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I was a Cali Smog Tech for about 10 years.... so trust me I don't know sheit!

But, FWIW....

A "porperly running engine" will produce no more NOx than 300ish under "normal conditions".
So, a new cat may burn more NOx than the old one but you're not fixing the problem.

NOx is formed durring combustion when cylinder temps are high. 1800* is when it starts to form IIRC. (probly wrong about that #)

The primary job of the EGR is to lower cylinder temps by recycling a inert gas through the cylinders.
MOST NOx failures are coused by a EGR problem of some sort.
Usually low flow. But since yours doesn't use a EGR, well...... I dunno.

One thing's fo sho, something's causing excessive cylinder temps.

"Will higher octane fuel help reduce NOx?" Yes! Higher Octane fuel burns cooler so it could/should help, but probly not much.

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And another interesting and informative post:

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Since I ran a shop for 8 years, worked as an Automotive Anylist for product development for an advanced OBD diagnostic software company... I prolly dont know **** either... but I will take a stab or 2...

A cat may very well fix the symptom of too much NOX as there are nox scrubbers in most converters.

However note that I said symptom, As has been stated previously high NOx Is a result of high combustion chamber temps.

Running Lean results in high combustion cyl temps.
Running Rich results in lower combustion cyl temps.

Things to check

#1 O2 Sensors. You may not get a code for a sensor, This does not mean that there is no chance of a sensor problem. Lemme splain

The way that I used to explain this, even when speaking at the Clean Air Conference in Boulder this past year is as follows.

Think of the way a narrow range O2 sensor works like a football field. The sensor should fluctuate right around the 50 yard line so long as Short term fuel trim and long term fuel trim are in the correct range. However using the OBD2 system it will only set a code if it repeatedly finds itself way down in the endzones. It can operate in the "grey area" on either end without setting a code. This will cause the fuel trims to be off, which can result in a lean condition that can cause NOX gas to be too high.

If you would like information on how to test for this just post up and I will write it out for you. Assuming you have a scanner that will show you "Mode 6"

#2 Vacuum leak... pretty self explanitory, however you would likely have a code.

gabe

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Treat the symptom, or find the cause and thus the cure. Just like health.