My car failed the first go-round of the new strict Dyno emissions test in the D/FW Texas area. HC, CO, CO2 and O2 were all well within limits, but the Nox was too high at the 15mph test. 25mph test it passed.

The inspection guy says that the normal cause for high Nox is bad cat or bad EGR function. I just put all new exhaust including a cat last November, so I figured it must be the EGR. I have also been experiencing pinging so bad that I have had to remove a lot of timing in my chip, so this also indicated EGR failure.

I bought an EGR valve and put it on.

I went back to re-test and the car failed both the 15mph and 25mph test this time. I noticed that he was leaving the car in Drive when he did this, so the rpms were around 1200 in second gear for the 15mph test, and 1200 in Drive for the 25mph test. WHen programming my chip, I noticed that it takes 4% throttle to enable EGR function. I hooked up Diacom and at 1300rpm in Drive, it only takes 2-3% throttle to go 25mph. I asked the guy if there was any reason he could not run the tests in first gear and second gear and he said as long as it was under 2500rpm it didn't matter. So looking at Diacom again, I see at 15mph in first gear, the engine is at 1800rpm. At 25mph in second gear, it's at 2000rpm. I have him do the test again holding it in first for the 15mph test, then second for the 25mph test.

Here are the results:


<BLOCKQUOTE>code:<HR><PRE>

Nox readings
first test with Bad EGR:

25mph test:
limit reading
1047 875

15mph test:
limit reading
1146 1248 Fail


second test with new EGR, but not enough throttle to enable EGR:

15mph test:
limit reading
1047 2039 Fail

25mph test:
limit reading
1146 2648 Fail


Third test with new EGR and Throttle Position high enough to enable EGR:

15mph test:
limit reading
1047 342

25mph test:
limit reading
1146 318


</PRE>[/QUOTE]

So, you can see that the EGR when properly functioning with a good catalytic converter, reduces Nox emissions very well! The car runs much better now as well with much less pinging.

A great article was mentioned in a post recently that explains a lot about EGR and how it works. Nox is a product of high combustion chamber temps, so it's hard to get rid of when trying to reduce other emissions because running lean makes it worse. Running a bit on the rich side will help reduce Nox, but then CO and CO2 goes up.... it's a fine balancing act to get them all right.


anyway, hope this helps someone that might be experiencing the same thing I went through.... short story: If you have high Nox, get a new cat, and a new EGR and make sure the test is done at a high enough throttle position to have EGR enabled!


:cheers:

 

Thanks for the info!

 

Good Info. Thanks Millions !!! That's just good stuff to put into the mixing pot !!!

Neal

 

Did you use a burned chip for the test? If so, why not just use the stock chip for the test, and swap back to your burned chip after test?

Just currious if this is going to give me a problem when i move back to California.

:chevy

 

I kept the same chip in there that I normally run, which is very close to the stock chip except for fan temps, idle speed and minor WOT fuel settings. The only change I made after failing the second time was to pull some timing out at the RPM's the test was run at, and enable EGR at 1% instead of 4% throttle just to make sure it kicked in.

 

Great thinking there..good info for when I get to that point.

 

Ya gotta luv the OBD-1 cars. When I get into burning the chips ill have a spare labeled
“ California SMOG test only”

:chevy

 

Great info, just wish I knew this 2 yrs ago. But Im do again next month.....I read a post about using DRY GAS ADDITIVE. How does that work? :crazy:

 

Is there a way to switch a vette with an lt1 into a "limp mode" where it only runs on half the cylinders or anything? I'm just curious because of experience with some other cars/engines/after market engine management systems.


[Modified by kspurr, 12:25 AM 10/4/2002]

 

Excellent info.. thx :)

 

Is your car a 49 state car? When I tested here in CA my car only had to meet Federal standards.

 

Out of the 50 states, California has the strictest emission laws. So be wise on what u do if u move back California :nono: