Emissions test on 930 - failed today

[arrivederci]

I put the cat on my 930 last night, but left the mixture as is. I did the VA emissions dyno run and passed HC and NO pretty easily. CO was high...so I failed.

                              15 mph                            25 mph
                    limit     reading   result       limit    reading   result
HC ppm        167       52         PASS       162        55         PASS
CO %           0.94     2.00       FAIL        1.04      2.07        FAIL
NO ppm       1273     211        PASS      1163     2 05        PASS
RPM                       2050      VALID                   1999      VALID
Dilution                   16.0       VALID                   16.0       VALID


I've heard that when CO goes down, HC goes up. Don't know much about it, but do know that I can reduce CO by leaning it out. Can anyone point me to the mixture screw and adjustment procedure (without a gas analyzer)? I've been told to lean it out until the idle gets a little rough...

[911Brian]

Josh,
I didn't know there was an emissions test in VA. I live in Richmond and have never heard of this.

[beepbeep]

Had same problem...4.9% CO (!!). Went to shop and said: "adjust the CO please" Got it back and they said "it was nothing wrong w/ CO , just warm it up really good before you sniff-test it".

So i warmed it really good and it went trough w/ 0.1% CO (and probably heaps of other polutants, but they didn't care for that beacuse it was old car). Jocke did the same, 0.1% for him as well...

My 930 had a small adjuster already inserted in fuel-distributor that could be turned for CO-adjustment. Otherwise, long hex key works. It's very twitchy and sensitive. Also, CO will change after you plug out the key so be careful.

[tsuter]

HC goes up as CO goes up.
NO goes up significantly when CO is low.
By your data you have room to lower your CO with room to play.

[rick conrath]

Lean out the mixture. I went through emissions in Mclean last year and had to tweak the CO on the spot. The car would not pass initially, you could smell the rich mixture. After adjusting the mixture in the parking lot, the readings were well below the standard(even better than my SC with the air pump and cat installed). My car is a '78 930 without air pump and cats, K27 with B&B headers. They just did not know what to look for, so the sniffer was all that they focused on. I had installed an air fuel ratio meter in the car, so that helped me tweak the mixture. With some practice, you can almost smell when the car is running right.

[Bill Verburg]

HC and CO move together NO_x moves opposite. To correct the HC & CO get the engine hot and get l = 1.2 &#177 0.1 i.e. lean it out

[lendaddy]

Move to Michigan, the weather sucks 5 months a year, but no sniff teats!

[Wayne 962]

Yup, lean it out for the test, then go back to the shop and adjust it to factory levels...

Too lean (espeicially on a Turbo) can cause severe damage...

-Wayne

[john70t]

From what I've heard-

If its lean, the HCs will be very high because the fuel particals are too far apart for the flame front to jump from one to another and the CO will be almost nothing.

When a little richer than stociometry(sp?) which is 14.7 to 1 and the "prefect mixture", the CO will rise a little but HCs will drop.
This is usually the safest setting for many vehicles.

When way too rich, the CO will go way up and the HCs will go up because of a slight rich misfire.

--CO is a completly burned mixture with too litttle O2 to make CO2.
--HC is raw gas vapors not burned in the cylinder-either from too rich, too lean, or ignition misfire.

The 2way Cat converts both to CO2. The 3way also converts NOs to N2 and O2.
Todays cars are designed to toe the line on the lean side, with the CAT taking care of the Extra HCs left over. 0% CO and 0ppm HC is not uncommon in the better ones.

Either way, too much raw gas in the cat will clog it up and make it glow cherry red. Something to consider when tuning it yourself.

[ChrisL]

VA emissions tests are only for certain counties -- presumably those with a pollution problem.

Chris.

[tsuter]

The only people who scare me more talking about chemistry than scientists are non scientists.

[Bill Verburg]

Agreed!

[tsuter]

Your post actually didn't "scare" me Bill.

[rick conrath]

Mclean, Viginia...emissions....no question. E-mail me if you are looking for an emissions station in the MClean area. I know the owner of a station on Springhill road, and they always treat me fairly.

When I went in for my emissions, the car was running very rich, you can smell it. Learn how to lean up your car, take the test and then fatten it back up for safety. If your car is in relative good health, you should not have be having Co issues.

[Bill Verburg]

tsuter, I know

[stlrj]

Bill,

HC and CO do move together, agreed, but there comes a point where the mixture becomes so lean that HC's start to move up again due to lean misfire. That may be what the smog tech may have been referring to when trying to explain it to the customer.

Regs,

Jose

[john70t]

Would "turn the screw thing on the distributor until it sounds about right" have been a better answer?

[Bill Verburg]

stlrj ,
Do you suppose that l = 1.2 &#177 0.1 has any bearing on the desired fuel air ratio for minimun HC & C0

Unfortunately it will also maximize No_x

The minimum values for No_x are obtained at l = 0.8 - and then again at l = 1.3 +

[john walker's workshop]

is the smog pump working, or is it gone? the belt teeth often strip off, so the pump doesn't turn. or it could be frozen. that, along with the oxygen sensor plugged in, and the CO adjusted to pass by a local shop with a sniffer, generally get you by.

[stlrj]

Bill,

It may not be necessary or even recommended to run a turbo that lean in order to pass emissions.

Regs,


Jose