Upper engine (intake) too cold, NOX too high
 

Hey guys :waveman:

I've been having a hell of a time passing smog. Now, my mechanic is telling me that my lower engine is ~ 210* and that my upper engine (intake) is ~ 150*. Since it's so cool, the computer isn't in closed loop and I'm running lean which is making my NOX go through the roof (2000+). Does this sound right?

He told me to replace the thermostat, which i am, but can you guys think of any other reasons my intake is so much cooler? Does what he said make sense?

As usual, :thanks:

If your coolant temp is around 210* and the engine's been running more than a few minutes, then you're definitely in closed loop unless the O2 sensor has gone bad. High NOX is probably from a non-functional EGR valve (or some other component of that system) or possibly a bad catalytic converter. Your intake manifold shouldn't get really hot, especially the plenum which doesn't have any coolant flowing through it. Sounds like it's time to find another mechanic that understands fuel-injected engines and how to properly diagnose them...

EGR system is completely replaced, from the solenoid, valve, and vacuum hoses. EGR system tested OK. Both my cats have been replaced. New plugs & fuel filter. I bead blasted the plenum clean. I've run seafoam. I've set my timing to 6* BTDC. I don't know what it could be anymore... except for timing chain.

all my other levels besides NOX are fine.

bad ground somewhere?
would a faulty injector do this?
weak fuel pump / fuel pressure?

timing chain?

i believe the EGR will start working around 130 degrees.
the cats only clean up a small amount of NOx, with your NOx that high, its something with the EGR system.
where do you have the vacuum for the EGR solenoid hooked up at?

I bought a new vacuum line from the EGR Valve to the solenoid. The vacuum line plugs in underneath the plenum towards the throttle body.

is it plugged in right around where i circled at in post 12 here?

https://www.thirdgen.org/forums/tpi/...pass-smog.html

the port should be on the throttle body it self.


check the vacuum from that port with a vacuum gage, it should not have vacuum with the throttle closed, but it should have vacuum when you open the throttle, you don't need to open it much to see if it does.

Post the exact emissions chart that you would have received.
I'm going to assume non closed loop operation. So yeah, replace the thermostat.
Are the fans turning on/off correctly as well?

Get rid of the "performance chip" as well if it's some aftermarket piece, that's probably 3/4 of the issue right there.
Overcooling will prevent closed loop, and don't put a new 160* thermo in there either, go with a GM 190*

stock chip is in. and a factor 195* thermostat is there too. i bought a replacement 195* stat that i'll install tomorrow.... but i doubt that's the prob