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Anyone familiar with smog test results?

blu67

blu67

Well-Known Member
My '96 4Runner failed smog again...(2nd time in a year) and this time it doesn't seem to be the cat. Any ideas as to what a high "NO" reading indicates? Could this just be a sensor issue? I just want to have some info in my pocket when I get it to the shop to be fixed.
THX
 
NO stand for Nitric Oxide, or more commonly Oxides of Nitrogen (NOx). What temperature is the car running at? The major reason for higher NOx is a high combustion temperature, normally above 2400°F. Bring the temperature down, this will bring the NOx down. Things like high compression and lean mixtures contribute to high chamber temps, as does over-advanced ignition timing. But there is a side effect...the CO number will go up. NOx and CO are inversely proportionate.
 
faulty EGR valve can affect NOx output, right? The exhuast piped back into the combustion chamber brings down the combustion temperature, bringing down NOx levels. But usually if an EGR valve is bad, you'll get a check-engine light. You got a clear computer? I would expect a '96 to be able to report a faulty EGR.
 
Could driving around a bit before the test warmed up the car too much? I was always told to be sure the car was plenty warm before the test.
 
Chris,

PT me and let's talk. I can help you as I just went thru a similar situation on our 88 Alfa Romeo (self induced)....

This will be fun as your vehicle is a non-OBD-II system...
 
"AtlantaSteve" said:
I thought OBD-II started in '96??? Or was it different for trucks?
Click to expand...
Yeah, I thought it was federally mandated for 1996, except for uber-heavy-duty vehicles? I've worked on some 1996 pickup trucks and they were all OBD2.

Edit: On second thought, one of them was a 1-ton HD big block dually pickup and it was OBD2. Hmm...
 
I type corrected. It did start in '96 (I had thought 98). That makes it even easier as I have an adapter to connect my laptop to the computer. Chris, my offer still stands. I can help you. PT me.
 
How long has it been since the last cam belt change? IME, a stretched belt *can* send emissions wonky without throwing codes. Had that issue with stbx's '96 Acura and my mom's T-bird.

Next place I'd look is EGR, but that should throw some codes. Good luck :)
 
As what others have stated, engine running hot, timing over advanced, inoperative EGR system, running lean for whatever reason, I'll add one more thing. Your catalytic converter could be bad also.
I would check it for codes and go from there.
 
Well, shop called back. $324 for bad O2 sensor on "right bank". He says it's working but working slowly. My gut calls BS. How does an electric sensor work slowly? Doesn't it either work or not? Anyone know the difficulty in changing this sensor?
 
O2 sensors do go bad. I've never worked on a 4Runner, but I've changed out a many O2 sensors. They are a piece of cake to change. Undo the wiring harnes, and unscrew the O2 sensor from the tailpipe. Do the opposite to install the new one. Done. $324 sounds a little steep in my book.
 
I changed both mine on my 1999 Camry 3.0 V6 with Bosch units from Advance Auto. Been fine ever since. Job was easy to do, but the one on the front manifold was WAY easier than the back!!! You should have no problem with that, though, as your engine isn't in there sideways(I don't think it is, at least)
 
Buy your O2 sensors at Rock auto. They are cheaper and just buy the Bosch brand. Installed a set on my friends Honda and never had a problem since.
 
Aftermarket will be fine.

O2 sensors get lazy. The ECM is looking for a certain number of sweeps from whatever it's minimum voltage to it's max. I think your car is looking for .1 to .9 volt but actually they usually sweep from .3 to .7

On that era of sensor we looked for 8 sweeps in 10 seconds at 2500 rpm.
 
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