srh1996

I'm having trouble passing smog on my 95 tacoma. When it's tested at 25 mph, all readings are good. At 15 mph, I have high HC and NO which made my truck fail. I replaced the O2 sensor 2 years ago when i smogged the truck. What could be the cause of the high readings on the low end. Any help would be appreciated.

grimpy

No idea but I smogged my vehicle last week at the request of a buyer that ended up being a no show... I replaced my O2 sensor 6 months ago and I barely passed that test... I was 1 under the max... The new CA smog is a POS... I know numerous BMW E39 5 series owners having a tough time passing it.

surf4runner

try testing w/ a 1/2 tank of 91.
be sure your at operating temp. and do a couple of WOT runs before you drop it off.
full tune up if it fails again.
hth

96RunnerSIB

Change your oil too help and also if it is really high slap in a cat converter they are cheap and help alot on no and hc
the 91 octane wont help alot but will make a small change also make sure that the car is up to temp and like Surf4runner said make sure you do some WOT runs or even just keep the thing above 3000 rpm for a few minutes before taking it in will help.
Also you may try another place because alot of places will come up with derferant results with the same car only an our apart.... I have tested mine at work and then gone and get it smoged and the reading was way diff.

96RunnerSIB

and this sounds really silly but it is very inportant too.... make sure they are not trying to do the test in over drive. they should only be testing it in 3rd gear. this changes the rpm of the engine and also the readings.

nightsurfride

Well, you say you failed for high HC and Nox? Hc indicates unburned fuel. Nox is formed by higher than normal combustion chamber tempuratures. The O2 sensors will not report a rich condition enough for the PCM to cause an unburned fuel issue. You would see high CO first off. What are the exact readings from the test. I need O2, CO, HC, NOX, and CO2 at 15 and 25. If all were elevated, even though it only failed for NOX and CO, and CO2 is lower than normal, I would test your catalytic converter for efficiency. Typically if you have higher HC your combustion temeratures are going to be lower and therefore you will not have high NOX. Let me know what all the readings are, and I will let you know the most probable causes. (I was a smog tech. for 5 years from '01 to '05)

Finelygotone

Sounds like your cat is bad - I had a 96 Tacoma - same thing - new cat=pass....but, like nightsurfride says, the exact readings would help to pinpoint the issue(s)...

srh1996

15 mph...CO2 %=14.48, O2%^=.24, HC=97(91 max), CO%=.35(.69 max), NO=806(527 max)
25 mph...CO2 %=14.50, O2%^=.12, HC=40(56 max), CO%=.19(.83), NO=268(780 max)

SpikeStrip

Also, if you need a CAT, CA offers an assistance programe to help pay for the smog repairs....

http://www.breatheeasier.ca.gov/failed.htm

Up to $500 !!

I used it to get a '90 Trooper I had to pass. You have to take it to a place on the state's list. Fro my Troop, they put on a new CAT, (old one 2 years old), passed the car, charged CA the Maximum and I was out... The programe is a total State rip off, but I got my certificate and some of my tax money back!

S.

nightsurfride

Even though co2 is looking pretty good, (co2= a complete burn in the combustion chamber. The higher the co2 the better your engine is burning the air/fuel mixture.13% to 15% ussually shows a well running engine system.), I am still leaning towards a week catalytic converter based on an elevation of all the other gas readings. You have left over o2 and left over HC and CO so the cat. should be taking these leftovers and converting them together into co2. The cat. should be storing the o2 from the nox so the nox reduces and then releasing it for the HC and CO. Based on the readings, it really does not seem to be doing a very good job of that. A gas anylizer or smog machine is needed to comfirm the cats inefficiency to provide the proof of the diagnostics, but the readings are pointing towards a tired cat. The question is why has the cat failed. If you had a missfire in the past for any given amount of time, that can greatly reduce the life of a cat. Bad O2 sensors can cause the fuel trims to bias rich which can over work a cat. Anyway, the short term answer seems to be a cat., but I would take a close look at your secondary ignition, MAF sensor, fuel trims, and O2 sensors to make sure your new cat. does not live a shortend life. Good luck, and let me know how it goes.

srh1996

Well I passed my smog. I ended up trying this chemical from Autozone called Guaranteed to Pass Smog (in a grey box). You dump it in when your tank is full, run it till it's empty and then you fill it up. I used 91 octane gas and i bearly passed. $7 fix in lieu of nearly $1000. Unfortunately, i have a 95 tacoma with CA emissions and an OBD II computer so i was quoted nearly $800 for the cat alone. I looked on the net for a while, but most of the cats were not for CA emissions. Thank you for the helpful suggestions!! Looking forward to contributing more on other issues.