High NOX - EGR?

[CT-C4-92]

Hi all,
My 92 LT1 failed inspection for the 2nd time.....high nox. I am thinking it is EGR related, as I have replaced everything else.....

Question 1 is, do I just the replace the valve itself or do I also replace the vacuum solenoid?

Question 2 is, how hard are these jobs?

Thanks! Much appreciated.

 

[Hib Halverson]

A problem with EGR is only one reason a car will fail an emissions test with high NOx.

NOx is created when there is nigh combustion temperatures. Exhaust gas recirculation (EGR) cools the combustion process thus lowering NOx.

First thing I'd do is read the factory service manual's information on the EGR system then run the EGR System Check listed in the manual. That will help you determine of the EGR valve is, in fact, faulty.

If you don't have the Factory Service Manual, you can order them from CAC Sponsor Zip Products.

 

[CT-C4-92]

A problem with EGR is only one reason a car will fail an emissions test with high NOx.

NOx is created when there is nigh combustion temperatures. Exhaust gas recirculation (EGR) cools the combustion process thus lowering NOx.

First thing I'd do is read the factory service manual's information on the EGR system then run the EGR System Check listed in the manual. That will help you determine of the EGR valve is, in fact, faulty.

If you don't have the Factory Service Manual, you can order them from CAC Sponsor Zip Products.

I do have the manuals. I suck at using them! I am thinking EGR because I have replaced just about everything else I can think of. Injectors, opti, cat, O2 sensors, maf, vacuum lines, plugs, wires, and probably some more stuff that I have forgotten!

 

[Hib Halverson]

Well...if you suck at using Service Manuals, I really don't have any additional suggestions which are useful other than to suggest Rockauto.com as a parts source.

Good luck.

 

[1cooldaddyo]

I'd say EGR is a good guess. THe valve itself is just a vacuum diaphragm. I've never seen the diaphragm tear, but I have seen the valve stick shut.
Take it off, and see if you can force the the plunger back. If it moves, I would then look at the relay or vacuum line itself.

I fortunately haven't had to do emissions testing in a very long time, but the last time was quite educational.
I had an '84 Monte SS that was running a Holley carb and no cat. Before I sprung for a new cat, I thought I'd see how close I could get without it.
THe local Precision Tune let me hookup to their analyzer and we started leaning out the idle mixture, hydrocarbons went right down, but we hit a point where to get the HC down to spec, the NOX went up.
I could have one but not the other. Later, I found out that if I had pulled some timing it would have brought the NOX down I probably could have squeaked through.
I guess my point is Lean=High NOX, Rich=Low NOX. Probably because rich is cooler combustion temp, but pulling timing sort of simulates rich without actually being rich.