I have a 96 302 auto with 239,000 miles. I have owned this Bronco for 2 years and driven maybe 2,000 miles since buying it. I had to get an emissions test today and failed due to high NOX.

Since I have owned the Bronco I replaced the entire exhaust system with Bassani headers, cat y-pipe, and cat back, replaced all 3 o2 sensors, changed all fluids, filters, plugs, wires, cap, rotor, and coil. The Bassani exhaust system was ment for a 95, no one makes anything for the 96. I relocated the manifold O2 sensors to the y pipe just below the connection to the header. Added a bung for the down stream sensor after the cat. Truck runs great, no CEL.

Anyone have tips or tricks to lower NOX without having to change my exhaust system?

 

Nox = things too hot in the combustion chamber. Mixture, timing, EGR all influence that number.

How is your HC and CO?

 

 

Check for vacuum leaks. Including manifold to heads.

 

So you have a Check Engine Light failure? Does that mean your check engine light is on?
If so, have you tried to pull codes from the computer?

 

do an oil change and bump the timing down to 8*btdc with spout removed.. then plug spout back in. Make sure the motor is good and warm when setting the timing. Make sure the engine is well up to temp and you have run it so to clear out any crud.

 

No I don't have a check light on. I'm not sure that ment.

 

Changed oil 30 min prior to going and testing. I hadn't driven it in months prior to getting tested. I'm going to drive it to work and home 70 miles round trip. I put a bottle of that CRC Guaranteed to pass stuff in. I will drive the **** out of it for a few days and put fresh fuel in it and try again.

 

OP passes on HC. Fails on Nox. Nox is the result of high combustion temps. Timing can cause it, so set the timing to the factory spec if it's not there now. Lean condition can cause it. Check for vacuum leaks. High engine temps can contribute to it. Make sure you are not overheated or have too hot a t-stat.

https://www.motor.com/magazine-summa...eptember-2005/

https://www.smogtips.com/failed-high...tric-oxide.cfm

If your cat is red hot that will do it too.

 

Don't forget about the EGR and the tube going to the exhaust manifold. the passage in the intake too. is this a idle or cruise test.

 

the 96 doesnt have EGR

 

Yes it does. The 5.8L engines do not use AIR injection. Not sure about the 5L for AIR injection use.

 

you beat me to it, and like you said it does. its been modified with a dpfe sensor.