failing emissions (nox)

[brad bryden]

hi my 87 suburban with a tbi 350 is falling emissions under nox. I have rebuilt the tb it has new injectors,map sensor,tps,egr valve,plugs and wires any ideas?? (hc) any help is greatly appreciated pass 1.53 can be 4.00 (co) pass 5.73 can be 40.00 (nox) fail 8.77 can be 5.50

 

[4xcrazy]

Last couple of times I had issues with NOX on a few different vehicles, it was due to a bad or clogged EGR valve. You say you replaced it, did you get a factory replacement or one of those that fit the engine, but require you to place a little washer, restrictor thingie in there with it?

Possibly the EGR solenoid isn't working properly?

 

[brad bryden]

i got a duralast egr before i put it on the (nox) was at 10.54 then dropped to 8.77

 

[brad bryden]

the motor only has about 15k miles on it but sat for years

 

[4X4HIGH]

New CAT will clear it up.

 

[brad bryden]

wouldn't the other things be high too if the cat was bad?

 

[rampage]

Do you have stock exhaust manifolds or headers?

 

[brad bryden]

stock exhaust manifolds.

 

[bubba blazer]

Just went through this too (high nox). It's indicative that the combustion chambers are getting really hot - 2500 degs so maybe the fuel is too lean or you have a vacuum leak. What I did was retard my timing (I think around - 4) and ran 101 octane boost and it lowered it. My brake booster was also leaking.

This link suggests other things to check:

http://www.smogtips.com/failed-high-NO-nitrous-oxide.cfm

Good luck! I hate smog checks (although it reminds me to do maintenance on my older vehicles).

 

[brad bryden]

i got her to pass i just had to retard the timing thanks!!!

 

[bubba blazer]

cool! thanks for the update - glad you were able to pass smog. unfortunately, the NOx in my truck is still borderline so I have a feeling a new cat is in my future...