I failed the NOx check when I got my check done yesterday. My other 2 values looked good. The CO% was 0.07% and the max allowable is 0.65. My hydrocarbon level was 6 PPM and the acceptable level was 51. The levels at 15 and 25 MPH were very similar.

My NOx was 571PPM at 15 MPH and 457PPM at 25 MPH. The acceptable levels are 512/765 PPM respectively, so I failed the 15MPH NOx level check. I looked at the previous Smog Check Report I had for my 4Runner and the NOx was 500PPM, so it just barely passed in 2007.

Is this likely my Catalytic Converter or my O2 sensor or both? I know that there is 2 parts to the Cat. Part 1 changes the NOx to N2 and O2 and Part 2 converts the CO to CO2. Is it possible to just get the part of the catalytic converter changed that eliminates the NOx or do I have to replace the whole thing?

Also is it legal to just go retested and hope things pass the 2nd time? I am afraid this going to turn into a $1000+ problem. How much does a catalytic converter cost to replace roughly?

 

it is the cat.

 

Definitely the CAT. Then EGR. O2 should not be the issue if other levels were good. But the CAt is your fix. OBD2 cat shouldn't be more then $300 installed, and thats on the expensive side.

 

Was the engine/cat thoroughly warmed up when you took the test?

 

What rig are you testing by the way? Im sure it was warm. Most places will make you run your car for awhile before you get on the sniffer.

 

You could try setting your timing back a little bit....get those cat's nice and hot. The other tricks like methyl hydrate/rubbing alchohol won't help with your NOx level though.

 

I am driving a 1998 4runner SR5. Need to put that in my signature. Has anyone in CA had to get their cat replaced? Alot of catalytic converters aren't legal in CA. I don't know why, but I can only assume the CA ones are significantly more expensive. Where can you buy one so I can see what the prices are?

Oh yeah, my 4runner had been running a while before I got it tested. I did have 4 cars in front of me, so it may have taken 30 minutes before it was put on the machine. I don't know if that is long enough for it to cool down.

 

Main thing that controls NOx is the EGR valve. Likely it is clogged or the actuating mechanism for it is not working properly. I have this very issue in my '85. It has a brand new O2 sensor and cat (from Toyota even) and passes all the other tests with near 0 readings, but NOx is right up at the limit. I find retarding the timing a few degrees and running premium fuel for the test lets me pass. This time around, instead of just cleaning my EGR valve, I plan on putting in a brand new valve hoping to drop those NOx levels down as far as I can. I do test mine hot, driving 10-20 miles before the test and then keeping the engine running while waiting for the test.

 

CA cat. converters have to be CARB and OBDII approved...just make sure it has that approval when you're looking for one.

Check out Bear River Converters...

 

OK thanks, didn't catch the estimate earlier.

Oh forgot to mention that there is no EGR valve on the 98 4runners. At least that is what the guy told me at the smog station.

 

Hey King I am having the same issue with my cat I believe. I am throwing a P420 code and was wondering if just replacing the 2nd cat would solve this issue. Did you solve your issue by replacing just the one ?

 

My own '98 failed on NOx at just 120k. High NOx is a sign of higher combustion temperatures which might be caused by carbon buildup. By all means, make sure your plugs, wires, MAF, are good, but before you run off and spend $$ on replacing the cat, why not do a simple $20 carbon cleaning? Heck do it twice! It fixed my NOx problem and has been my standard prep before every smog check. My most recent reading is very close to the limit but it has always passed. Can't argue with 16yrs of success. https://www.yotatech.com/forums/f116...l#post50631481