My friend's 97 4Runner did not pass emissions. They said the NO level too high (Nitrogen Oxide).

What would cause it to be too high?

Bob

 

NO bottle in the trunk

 

Sounds like maybe something with the catalytic converter - I JUST read up on this today too!

Towards the middle of the page is what you'll find interesting:

http://auto.howstuffworks.com/catalytic-converter2.htm

 

high NO often is from EGR not working properly, that's the first place I would start.

 

eric and pete,

ok, thanks. ill read up and check out the EGR valve.

bob

 

Ok guys,

I have his test results. Yellow box shows his NO was too high. Can anyone who knows interpret this? His CO is fine but the NO is too high---is this a more definitive sign that the EGR valve needs replacing?



Bob

 

Most cases it's the cat that has gone bad, most likely the EGR valve is fine, it would have came up in the inital inspection.

 

hey bruce,

the dealership and the parts guy i buy from both say there is no egr valve on the 3rd gen 4runners.

they suspect it might be the cat too, but they both recommended that i change out the plugs and wires, clean out the fuel injection system w/ BG44K, and change the pcv valve. don't know what that might really do but he needs to do this anyways.

bob

 

I just got emissions tested today. I've got the same issue.

The technicians gave me a document describing possible causes for failing the NOx test.

1) Inoperative/ineffective Exhaust Gas Recirculation System
2) Excessively lean AFR
3) O2 sensor malfunction
4) Engine deposites
5) Malfunctioning or missing catalytic converter (3-way catalyst only).

Did your figure the problem out yet?

 

Oscar,

We're still waiting for the parts to come in. We're going to install them and do some other maintenance work before re-testing.

I have a sinking feeling that it might be the cat.

Bob

 

Guys,

Just a follow up to this story: I replaced the front 02 sensor for him yesterday and he passed his smog test this morning.

http://www.4runners.org/articles/02sensor

Thanks for all the help and advice, guys!

Bob

 

and a write-up to boot

 

Hello all,

I just got myself failed this weekend as well. My NO2 was around 760 with 15mph. The smog technician recommend me to do an PCV replacement and clean out the fuel injection, do a test drive and retest. Guess what? NO2 now is only 300. Just want to share.

 

Mine too. NOS 1080 over a CA permitted 330. Bummer...

 

pepsi,

we changed:

- pcv
- fuel filter
- front 02 sensor

the first two had no effect on the NO2 reading (failed). when we changed the front 02 sensor, everything was oooootay!

bob

 

Bob,

Was there a reason why just the front O2?

 

pete,

thats what the diagnostic report said.

bob

 

Ah okay
I wasn't sure if the front because it's most likely to fail or what.