89 K5 (V10). Smallblock 350. High NOX. Smog fail. EGR? CAT?

[imiceman44]

with an OBD1 vehicle that is going to get the sniffer up the pooper... never ever ever take your vehicle to be tested unless:

1) it just had an oil change with good quality oil
2) the gas is FRESH -not 1/2 tank of something that was sitting- drain that garbage or drive around until it has been consumed, and then fill it up with NEW good quality gasoline
3)) the engine is FULLY warmed up when you arrive at the smog station.


I have literally been AMAZED at the difference old oil or old gas makes at passing a test here in CA, and dont even think about getting the thing tested if its not fully warmed up. You need the coolant at the correct temp, the heads needs to be hot, and the cat needs to be hot.


the only time my 1988 K5 ever came close to failing a smog test (well technically it did for a minute) -it had been sitting for a few months. I fired it up - jumped in, ran over to the smog place about 5-7 miles away. engine coolant temp was barely coming to temp when i got there. It failed in several categories by quite a bit. I was really surprised! what the hell- this thing always passes, and the cat is fairly new!

owner of the smog place came over and said; "has this truck been sitting? - go change the oil and fill up with fresh gas. come back and we will test again."
i was not sold on that making a difference and figured i needed a new egr, or cat... but i did it, and went back, and the truck passed with FLYING COLORS. the tech doing the test told me he was worried I was going to get him in trouble, and must have added something to the gas tank that was illegal. -NOPE!

Any more, why take the risk of not passing the test? - i drive around for quite a while before an emissions test, and spend some time driving in 2nd with the rpms up... and when Im sure the thing is HOT, i pull into the smog testing station and leave the truck running in their parking lot. it stays running until the tech goes and pulls it inside to do the test.

I second this.
Especially the old gas.

 

[Wes Harden]

Nox is result of high combustion temps. Anything that raises temperature will raise nox.
Exhaust gas reintroduced into the combustion chamber lowers temps, less to burn. Air injection at exhaust manifolds purpose is aid in the complete combustion of and unburnt gas as it leaves the cylinder, but some of that fresh O2 gets into the cylinder cooling it.
High compression will cause high nox. If there is a build up of carbon on top the pistons this can put you over.
Cooling system must be in good shape. Something as simple as a cap that holds less than required pressure can raise cylinder temps.
Advanced timing will raise nox.
In the 70's, I put hundreds of kits on 60's vintage cars. This kit eliminated the vacuum advance. Each car got a sticker on the speedo that stated not exceed 60 mph for extended periods. Better kits used a thermal vacuum switch, if the engine temp went over the setting it would allow vacuum advance.
Nox is why the original Hemi and air cooled engines went away.