Just failed Ga emission test. NOx extremely high. I need help pinpointing the problem since I never had to deal with emission problems before, I'm from Florida and we didn't have emissions there. I'm leaning towards a problem with the egr valve and doing a seafoam treatment. Let me know what you guys think.

25/25test 50/15 test
read allow read allow
HC 86 103 102 107
CO .33 .57 .36 .59
NOx 1970 712 2177 786

 

Definitely check your EGR system since its primary function is the reduction of NOx emissions.

 

Most of your readings are all pretty high since the limits are usually set for readings at 10% of the value normally.
I would say 100% you need new cats as they are dying , or your car was not heated up properly before testing which caused the cats to not be at optimal operating temp thus failing to convert as much.

If you know for sure they had the car hot before testing then do the next step otherwise you need a set of cats.
Sea foam and clean the egr and use regular gas not premium for the test . New spark plugs and oil never hurt either,

 

I forgot to mention this is a '94 LS400. I cleaned the egr valve and ran some seafoam through a vacuum line. Also my engine light was never on, so I'm leaning towards the cats like SK mentioned. Any more thoughts?

 

I had similar readings on another car, the EGR, is your first step. It will surprise you how much a change in emissions this part has. The EGR valve is not tolerant of gunk and any bit can plug it up. If the O2's haven't been changed do them also.

Cat's don't often fail. I had one fail on one of our cars and it was an old pellet type, not the mesh being used today. If a cat fails, it is usually caused up stream by another engine issue.

 

I drove around after the seafoam treatment and there's still some white smoke coming out. Already changed oil and putting my NGK plugs back in tomorrow. I'm thinking it will clear up after I drive it some more. And my egr valve is not vacuum operated like most Ls4's I've seen on this board. It looks like the following: http://www.autozone.com/N,16000214//...eResultSet.htm

 

There is one thing you might try and that is to take the car out on the open road and give is a good 30 mile run just before you get the smog test. This helps clean everything out I always do this on my 91 lexus with 192,000 miles on it here in California and the smog test here are tuff. I always take it on a good 30 mile run and drive directly to the smog test and no problem. Hope this info helps!!!!

 

I just tested mine last week with original cats and 325 000 on the OD.
It passed so good that i had readings of 0 for c.o.

 

One thing to keep an eye on is your intake throttle body in can clog up with carbon and this is a common problem for the new cars my 1991 lexus went in for valve ajustment they were loud and the tech found my intake throttle body full of carbon he cleaned it out and what new performace my car has. I have heard from several tech at lexus that the carbon build up is normal on all lexus MAKE SURE YOURS IS NOT BLOCKED UP

 

Just passed emissions! Changed out my cats. Thanks to everyone for the help.

 

Glad it worked out. What did it cost ? OEM or aftermarket?

 

Catco cats, cost me $260 for both, direct fit. $100 install.

 

Failed emissions again this year. Cleaned throttle body, cleaned egr valve , and ran seafoam through intake, then took it to test for a second time and failed again. After failing twice i'd like to know what you guys thought? Although it passes the 50/15 test the second time. No cel.

1st test
25/25 50/15
read allow read allow
hc 14 103 10 107
c0 .01 .57 .01 .59
no 1409 712 1356 786

2nd test
25/25 50/15
read allow read allow
hc 11 103 12 107
co .01 .57 .05 .59
no 1199 712 131 786

 

I know the feeling. Your problem is upstream of the cats and buying new ones each year is going to be a chore for each smog test. How many miles on your engine? I'm wondering if you now have wear issues effecting your emissions. Does it smoke at idle and/or while running?

My suggestion:
As simple as the EGR may seem, replace it this time and verify the EGR piping is also cleaned intact (no holes-cracks...). Check the resistance on the O2 sensors for function.

Also the coolant temp sensor...if this is reading wrong, it will send a different signal to the EFI computer for air-fuel mixture. Might as well change it since this is a low $$ fix.

 

I just smogged my car today and it passed. I changed out the O2 sensors a couple weeks ago. My car is a 93 and it passed very cleanly.

I would recommend doing simple maintenance and throwing on new O2's.

Maybe that will help.