What do these emissions readings mean?

Status
Not open for further replies.
Joined
Mar 16, 2003
Messages
3,690
Location
Colorado
I recently had my 1997 GMC Sierra tested by the state for emissions. 2 years ago the readings were lower across the board and seem to have jumped a lot this time around. The truck still passed but I'm wondering if I may have problems developing. It could be that maybe I did not drive the truck long enough(drove 10 miles to test center) for the test and didn't get it as hot as the prior test?

What do you think the numbers show? The top picture is the test from 2 years ago and the bottom is the new test:

 
GPM = grams per mile; the rate of each HC/CO/CO2/NOx you're polluting.
HC = hydrocarbon: essentially fuel/gas/oil
CO = carbon monoxide
CO2 = carbon dioxide
NOx = nitrogen dioxide NO2 and nitric oxide NO

It's fine if it passes emissions inspection, nothing to worry about. It just means that your vehicle is getting older and not as efficient as it used to be. Too many factors affect it: quality of gas, ignition system, exhaust system, catalytic converters, age, just about anything.
 
Only 2300 miles in 2 years? The truck sits too much, if you gave it a good road trip before going to get smogged, im sure the numbers would be a tad better.
 
Originally Posted By: Tman220
Only 2300 miles in 2 years? The truck sits too much, if you gave it a good road trip before going to get smogged, im sure the numbers would be a tad better.


The truck only gets used when it is needed but I ALWAYS heat it up fully before parking in the garage again. Gets driven about 100 miles a month.
 
Did you do any maint. prior to taking it in? Oil change, new air filter, plugs, etc. HIGH speed runs down the highway are a must, here in Cali on my 83 Silverado with 230K I do a full tuneup, Plugs, oil change, cap and rotor, air filter and clean out PCV valve, check timing and throw in a bottle of Guaranteed to Pass additive in the tank, she's passed all her tests with flying colors.
cheers3.gif
 
From what I see.. I'd say its burning alot of gas but according to the pollution standards when it was built.. not excessively polluting.

Sometimes a fresh oil change, fresh gas, and a hour road trip before testing will totally change all those numbers.

If the truck barely fails that is what I would do (your truck passed obiv)

If the numbers are wacked out and totally failed by a large margin.. it means you probably need parts or at least to fix a mechanical problem.. wiring etc.

A cat converter,MAF, o2 sensor etc.
 
10 miles isn't enough to get the oil up to temp this time of year, next time take it for a good run, the numbers will probably drop.
 
Catalysts can lose efficiency for a variety of reasons. Youre well within range, so my first guy is temperature. I wouldnt much worry yet...
 
Originally Posted By: ruhroh
Too many factors affect it: quality of gas, ignition system, exhaust system, catalytic converters, age, just about anything.


To be picky, there is no possibility age can affect it directly. The car doesn't "know" how old it is. I think you perhaps meant wear.
 
Originally Posted By: Tman220
Only 2300 miles in 2 years? The truck sits too much, if you gave it a good road trip before going to get smogged, im sure the numbers would be a tad better.


Maybe. Those are great numbers for a 20 year old vehicle.It easily passed and it's doubtful more driving would improve it much.Maybe the differences between the two tests is dirtier oil if it wasn't changed.
 
Last edited:
How hard do you drive it?

I used to have the same truck but a 96' and I drove it hard, they really get up and go!
 
In Older cars, you can greatly get different emissions depending on the driving when you bring the vehicle in. So Like if you brought it in cold and it hasn't had an oil change in awhile, you're going to get worse readings, versus if you just drove it 50miles and had a couple good pulls on it and car (and cat) was nice and hot and you had a tank of fresh chevron gas in it.

If you pass you pass. I wouldn't put too much thought into needing to drive it more just for the sake of driving for no reason. I would say driving 5 smoggier miles is overall better for the environment than 50 miles that are at slightly lower emissions.

Only put some thought into the "italian tuneup" and a long drive and the getting it in use the tank or so before you have your next test.
 
I don't drive it to hard at all. I do red line it once it is up to temp and merging on the highway to "blow it out". The oil was changed and only had a couple hundred miles on it when the test was done. It had sat for a month or so and then driven 10 or so miles to the test center. I though it was warmed up but maybe not. I'll drive her much farther next time! In 2 years she will probably only have a couple more miles on her.....want to keep her in perfect condition for ever hahahaha!!!!








 
Last edited:
Ignition deficiency makes all reading higher, except perharps, CO that needs a fine burn to occur, in spite of the catcon job.
That or stale fuel, months old. Next time fill it in with fresh.
 
Last edited:
What a piece of junk truck.

I think you better let me take it off your hands
laugh.gif


I haven't seen one of those trucks that clean since 2005!
 
What part of Colorado do you live in?

Denver and Boulder both have EPA reformulated gas requirements.
I saw an article from 2016 that indicated Colorado changed from winter blend gas at the end of February.
Maybe you have a different blend of gas?

Did you add any gas stabilizer to the gas?

http://www.denverpost.com/2016/02/29/col...mer-fuel-blend/
PUBLISHED: February 29, 2016

Gas prices in Denver and across Colorado experienced their “inevitable” increases during the past week and jumped by more than 12 cents per gallon, according to GasBuddy.com data released Monday.
“This is the market pricing in that premium for the more expensive summer blend,” said Will Speer, a GasBuddy senior petroleum analyst.
 
Last edited:
Status
Not open for further replies.
Back
Top