Trick414

Heya fellas!

I just failed the emissions test for high NOx. The numbers are in the attached image.

Prior to the test I did the following:
New catalytic convertor (CATCO from Summit)
Tune-up - wires, rotor, cap, ACDelco plugs
New O2 sensor
New temp sending unit
Pulled the intake for cleaning and degreasing, new gaskets - cleaned the EGR passages while there

The car runs fine, no codes, starts and runs easy. 100k miles.

I read through the tech article. I have vacuum at the solenoid. When revving the EGR opens (not much, but I was only at about half throttle). The EGR holds a vacuum with my vacuum pump.

So, I'm kind of stuck. I'm pretty sure the Cat is good, it is brand new and a brand that everyone here talks about. The EGR system seems to be working as far as I can tell.

The only thing I can think is that something else is going on causing high combustion temps - like running lean - but I THINK the CO and HC numbers look ok.

Last year the NOx numbers were highish, but still in the ok zone. This year, with a new tune-up and cat, I would think I should have hit a home run.

Anybody have any insight?

fallenleader

iTrader: (2)

https://www.thirdgen.org/forums/fire...t-my-84-a.html

i was running a double dose of fuelon "should get you through on its own" plus seafoam and stp carb injector cleaner. "all gas additives" all at the same time.

Trick414

Yes, I thought about throwing some stuff like that at it. I'm pretty sure I can get it to pass with some action like that. Thanks for the heads up.

Heck, I know I can get it to pass... I know a few guys that have shops...

But, I'm more concerned with what is actually going on.

Here are my theories so far:

1. The EGR system isnt working exactly right. I don't have a real good frame of reference, but the EGR seems to be kind of weak. First, when I went to check the EGR, I really had to muscle the valve with my fingers to "pop" it loose. Once it was loose, it didn't seem to move very much under half-to-heavier-throttle. So, it could be a stcky valve or a junk solenoid. But, again, I don't have any experience with this particular system, so I don't know. I'd gladly go out and throw hundreds of dollars at this to get it fixed, but I also want to work through it and find out the cause.

2. I replaced the O2 sensor about 1 month ago with one from Autozone. I don't remember, but I imagine it was a Bosch. So, based on previous threads here, the possibility exists that I got a bad one, and it has thrown my ECM off.

3. I got to the shop pretty early Saturday morning. I was the second customer. The guy before me was in about a 1992 Cadillac. I didn't pay much attention, but I did overhear that he failed. He "argued" a bit (nothing over-the-top) with the emissions tech because he had "passed" at another shop. Again, I wasn't paying much attention, but in retrospect I can only assume he had some work done elsewhere and they had an emission machine, but it isn't certified, and it showed him to have passed.

I didn't think about this until after I failed. Like I mentioned above, I passed last year with a horribly tuned car with a 1991 cat on it. I did a tune-up, new cat, new o2 sensor, etc, and fail... I have never heard of the machine being off, but it did at least stick in my mind.

Any other thoughts anyone?

JesterHead1651

a high nox level is the result of your timing. i know because my timing was advanced alot and i failed emissions for nox. you need to have the timing changed back to oem specs. when the timing is advanced it throws off the emissions equipement

Trick414

Thanks for the reply!

I checked the timing today. When I did the tune-up last month, I set it at factory spec 0*. Today, it was advanced approximately 1*.

Do you think one degree would throw me that far outside of spec?

Thanks!

91chevywt

The EGR's main function is reducing NOx. If it's sticking at all that should be your first area to fix. You can sometimes clean them since they often get clogged with carbon. They can be fairly expensive, not sure how much for your car. It's usually best to replace them if there is any problems. Or you could find someone who will make it pass for a certain amount of money. You will just have to do this at all inspection intervals.

fallenleader

iTrader: (2)

hmm, my chart said I almost failed the nox? right? All I can say is most of my vacuum is d'ced and been trying to connect it.

I passed by pure luck and despiration.

edit: I believe mine is bosch, cheapest one? black box?

DENN_SHAH

iTrader: (1)

im not impressed with the Bosch O2 sensors on the older GM cars, i've seen too many of them cause problems.

the motor is loaded more on the low speed test than it is on the high speed test.
normally if there is a problem with the EGR system, NOx will be much higher, but not always.
the EGR valve could be sticking, its not uncommon. the valve should move fairly easily. the valve should be fully opened by 5 inches of vacuum.
when i replace an EGR valve for an emissions failure or for a code 32, i replace the solenoid too. i only use A/C Delco parts.
make sure the vacuum source for the EGR solenoid is hooked up to the right fitting on the TBI. it should have no vacuum on it at idle but have vacuum at part throttle.
timing will affect NOx, pulling 2~4 degrees should show a fair amount of change.
any more than 4 degrees can start to have an adverse affect on CO & HC.
you could have combustion chamber deposits, a decarb treatment should take care of that.
i've not been impressed with a lot of with the aftermarket cats, some brands do great with CO & HC, but do poorly with NOx, others do good with NOx but not so good
with CO & HC. most of the CATCOs i've seen do ok on all 3 gases.

the machine could be off, but its not likely. they have to be calibrated every couple of days. if the machine wants a gas calibration there is no way to run the test without doing the calibration.
plus the state comes out once a month & does a calibration check on them.

Trick414

Hey all, just to follow up, I got a pass this weekend.

Here's what I did:

New ACDelco EGR and solenoid.

I tested the operation before and after the swap and it appeared to work exactly the same.

I filled up with mid-grade gas and poured in a bottle of "Greased Lightning Fuel System Treatment". I had put a bunch of gas in a few months earlier, but I think it was still mixed with some old gas that had been put in a a year or two ago. (I don't really drive the car, it just sits in the garage.)

The HC, CO, CO2, 02 all stayed relatively the same.

My Nox at high speed (25mph - 1209 rpms) dropped from 819 to 651 (821 max).

My Nox at low speed (15mph - 1278 rpms) dropped from 1406 to 907 (NOTE 907 was max...just made it!)

So, I saw a significant decrease in Nox and got it to pass, but only right on the line.

I'm not sure what caused the decrease...
1. New EGR system (not convinced the old one was bad)
2. A full tank of new, mid-grade gas to help dilute a few remaining quarts/gallons of potentially two-year old gas
3. The bottle of additive "Guaranteed" to reduce emissions.

In any case, I would love to figure out why Nox is still so high.

EDIT: Also, the machine made the tech run the test twice. He remarked on that fact, but he didn't elaborate and I didn't think to ask him what that meant.

Thanks!

fallenleader

iTrader: (2)

if you don't run the car much, when you finish this tank of gas "maybe before you do" get a fuel stabalizer. they're cheap and worth it.

right guys?

DENN_SHAH

iTrader: (1)

the machine will do a second chance test if the readings are just outside of the pass range. i don't know how much outside the readings can be out of range on the first run for the machine to do a second run, or if it will do the second chance if more than one gas is just outside of the pass range.
on the second chance test as soon as the machine saw the NOx in the pass range it ended the test & passed your car.

the old fuel in the tank probably had a lot to do with it failing the first time you took it in. over time gasoline breaks down & looses needed properties for clean emissions & proper performance.

if your going to let it sit for very long some fuel stabilizer in the tank like fallen said would be a good ideal.

if its going to sit for an extended amount of time, draining the tank would probably be a good ideal.
you can read about old gas that has ethanol in it here,
http://www.chron.com/disp/story.mpl/...s/5819751.html

fallenleader

iTrader: (2)

before ethanol was heavily used, there were still problems. I call the smell cherry "soon as I smell it, i announce it. smells like crap, nothing like cherries" when fuel spoils and gels up. small engine repair drove me nuts with all the gelled carbs.

thats the other big reason for the stabalizer?

I'm not 100% on facts, just a tiny bit of experience.