SC300AZN

Hey everyone! I have been reading the forums religiously for the last several weeks in hopes of finding help with pinpointing an emissions problem; I have read several great posts but still cannot seem to pass emissions.

Here's what I've done so far.

93 sc300, 220000 on the odometer

failed with slightly high hc, co passed, nox at slightly less than double the allowed amount

-plugs and valve cover (vc was leaking horribly, and pooling oil around cylinders 5 and 6),pcv valve,

failed with slightly higher hc, co passed, nox at 3 times allowed amount

-cap, rotor, o2 sensors (found bosch with a flange 1 wire, reused old connectors. replaced 2 mains, not gonna mess with the third), cleaned egr and pipe (got plunger to move again and removed a crap ton of carbon from the valve, temp sensor, and pipe), vacuum modulator (old one had a rip in the diaphragm),: changed oil.

failed with numbers similar to the first test, slightly high hc, co passed, and about double allowed amount for nox.

The only thing I can think of replacing that I have not done yet is replacing the cats. I have read some posts that say that toyota cats rarely go bad, some that say they do. Some posts say that the cats wont affect nox, some say it will. Some posts say to try denatured alcohol, and some say it will raise nox. I guess I'm looking for help and clarification on what my issue(s) may be. I just dont want to drop 600.00 (including labor) for new front cats if that's not the issue. Any ideas or recommendations? Anything I'm too dumb to see? Thanks!

tritron

NOx seems like cats. Did you look for any cracks in your air intake this will allow for more unmetered air to flow into engine. I heard that running acetone in gas tank will restore catalytic cats. I hear about people grabbing soap and water and washing cats.

SC300AZN

I have not check for any intake leaks, but I will now! I should probably take off and clean the intake as well. Ive cleaned intakes before, but not on an sc300. Are there any sensors that cannot take carb cleaner that I need to remove? Thanks again!

2jznosht

I swapped my 20 year old cat out and passed with flying colors...

Tam4511

iTrader: (9)

try cleaning out your egr valve, replaceding your vacuum modulator ($12 on ebay) and running some seafoam/ b12 through your intake. i did all of that when i had almost double nox and hc and it took me down to well below the limit.

Ali SC3

iTrader: (10)

if you have an old cat its hard to diagnose. now if you had changed the cat and had issues sill it would be easier to diagnose.
with nox that high I would check the ignition timing , make sure its not advanced. if everything checks out it may be time for a replacement high flow cat or something like that.
If you had just high HC and not the others it could be something like the tps, but to have high HC and nox means you have extra fuel and high cylinder temps, which wouldn't happen normally.

and with the egr pipe, if all that was clogged, then the part in the throttle body where the egr pipe opens to the intake is probably clogged as well. you need to clean the whole system including the parts int he throttle body, but that being said if everything was working you could pass nox easily without a working egr.

SC300AZN

Hey everyone,

Thank you for all of you help! I ended up replacing the cat and passed far below acceptable. Funny thing is it spent about 10 seconds on the dyno, so I thought it failed. When I took the old cat out, the center had melted in areas and deteriorated so much that it created an inch hole through the center. So thank you to everyone for your help, i really appreciate it!