My 351W (carburated) failed the Texas sniffer test with High CO.

All of the other readings were very low, so I am confused as to why the CO is high.
............................. Standard.......................Reading..........Re sult
HC(ppm).....................281................... ............50...............Pass
CO(%).......................2.26.................. ..........4.20...............Fail
CO2(%)............................................ .............12.2
NOX(ppm).................1980..................... ..........69................Pass
Dilution:..................... >6.0............................16.4.............. Pass

According to the emission guide at Autozone:
Carbon monoxide is formed when not enough oxygen is present during the combustion process to convert carbon (C) to carbon dioxide (CO2). An increase in the carbon monoxide (CO) emission is normally accompanied by an increase in the hydrocarbon (HC) emission because of the lack of oxygen to completely burn all of the fuel mixture.

Since the HC is so low l would not think the problem would be fuel mixture or a Cat problem.

Does anyone have any suggestions?

Thanks in advance for your replies.

 

This might seem silly but for some strange reason it worked. I had trouble getting thru emissions testing back when we had it here in Tampa, I failed twice by a slim margin. A mechanic friend of mine told me to do a oil change and air filter before i go again. Sure enough it worked, Although i don't remember the explanation he gave me all i can say is it could'nt hurt.

 

are you showing us
the loaded or idle readings?

 

The readings I showed were at 25 MPH on the chasis dyno

I also have readings at 15 MPH which are as follows:

............................. Standard......................Reading..........Res ult
HC(ppm).....................286................... ............56...............Pass
CO(%).......................1.64.................. ..........3.60...............Fail
CO2(%)............................................ ............12.5
NOX(ppm).................2125..................... .......112................Pass
Dilution:..................... >6.0...........................16.1............... Pass

 

I don't know if this will help, but here is my scenario: I just sold my 1970 bronco with a 1976 302 and I had the displeasure of having to pass Arizona emissions three times. The first attempt of each of the three tries was a failure, followed by some engine work, followed by success. 2001: Failed miserably, switched points to pertronix, changed oil, passed easily. 2002: Failed miserably, called Eric's Bronco Corral in Denver, instructed to retard the timing 5 to 8 degrees, changed oil, passed easily. 2003: failed idle readings, kicked up the idle speed, changed oil, passed easily. The third scenario probably will not be of any help for you. A few more things: when your sitting in line keep your foot on the gas and maintain high RPM's. Also, take the test with the lowest possible octane fuel you can find. You might have to mix and match some of these things, but you're not that far off of passing as it stands. Arizona has a department of environmental quality laboratory, where people who fail twice are sent for retesting. You can actually retest, check the figures, tweak the engine in the parking lot, and retest again for free as many times as you want until you get it right. Check to see if they have this sort of thing near you. Lots of luck.

-aaron

 

I had the same problem a few years back on a Jeep. It turned out to be a faulty egr system. It took me a few attemps to fix it before finding a web site explaining how excess CO can be a result of the erg. I would also check to make sure the mechanical/vaccum advance works in the distributor because they affect the spark timing and combustion efficeincy. CO is a sign of incomplete combustion.

 

I would guess that:

You have plenty of power.

You have no misfires.

Your gas mileage is somewhat poor (whose isn't with a 351) - what is yours by the way?

The high CO is in a rich (incomplete combustion) condition right now.

Your cat is fine (for now) because it is converting the excess HC. That is why they are low in emissions, but extended operation in this manner will not be good for the cat.

I think the oil change and air filter is a good idea right now to start.

Good luck.

 

Hey adunham,

How do you like that 280H in your truck?

Enough vacuum to run power brakes?

Nasty idle?

Does it make enough low end for street use?

Thanks, I'm trying to figure out the cam i want.

 

Well I Passed on the 2nd attempt:

Thanks to all of you that posted especially to Bill C that gave me the clue that I was just probably running rich.

For all that are interested, I changed the primary jets in my Edelbrock Performer Carb #1406 to calibration #12 according to the manual. This is 3 stages lean.

This is really a lean setup, and the engine coughs on heavy load. I do not recommend driving much at this setting.

I purchased a CO monitor at Wallmart (the kind you put in your home) for $39.95 and took tailpipe readings at 2000 RPM before and after I changed Jets. The readings indicated that I had reduced CO by 1/4, so I thought I was on the right track.

Here's the readings from the Emissions Test at 25MPH:

............................. Standard......................Reading..........Res ult
HC(ppm).....................281................... ............8................Pass
CO(%).......................2.26.................. ..........0.00..............Pass
CO2(%)............................................ ............13.5
NOX(ppm).................1980..................... ......322................Pass
Dilution:..................... >6.0..........................13.1...............P ***

With readings this low, I probably did not need to go this lean on the Carb, but it sure "Aced" the test.

The original "stock" Edelbrock calibration runs real nice with pleanty of power through the whole RPM range, so thats what I will go back to (until next year at Inspection time).

If anyone has any questions or needs any help with emissions testing I can recommend the following site that I found very helpful.

http://www.jason.fletcher.net/tech/sniffer/sniffer.htm
Especially section III on CO% relating to A/F Ratio

To: 1984_355w
I like the Cam. It has good vacuum for accessories and has nice low end torque. Idle is "nasty"

This engine was patterened after a buildup in Hot Rod Magazine Jan 2000 & May 2000. Hot Rod dyno'd this engine combo at 380HP & 395TQ.

See my Web-Site for info:
http://www.fabtechassociates.com/bigred/bigred.html

Thanks again to all that helped.

Jerry T

 

Had you passed the emmissions test before? If so something else changed in your system. Is the the carb a new addition from the last test? If so than you probably found the problem. If not than you passed your test but you still many not be running at peak effiecency/power. Your jets would not wear enough between tests to cause the rich condition so you need to find out what is causing the enrichment.

The egr system will cause a rich mixture when the valve sticks open causing a reduction in available oxygen because heated exhaust gas is drawn into the intake.

A faulty ignition system (mechanical and vacuum advance mechanisms) will also change the combustion dynamics.

Congratulations on passing your test. I keep my emmisions records and compare them to make sure my engines are running properly. I find they help to diagnos problems I would not normally find.

 

This is a new engine that I built and installed last year in Jan 2002. The engine is "built" with a big cam and performance heads.

I did pass the emissions test last year, however the test was run at idle and at 2400 RPM with no load on the engine.

This year Texas requires all vehicles older than 1997 to run the emission tests on a chasis dyno at 15mph and 25mph. In addition the emissions limits were more stringent.

As a note, my vehicle would pass the emission limits for the 2003 cars.

My emissions equipment included Cats and EGR only. No air pump, O2 sensors or computer management system.

I learned a lot about emissions and engine tuning from this experience.

 

Very nice truck. So did you get everything smoothed out and rolling again? I'm blessed to live here in Illinois, some people haven't even heard of emissions!

 

get a fresh cat and use it for testing only, fresh cat works five times better the first few hours of its life.

 

To: 1984_355w

Thanks for the comments on my truck.

I have 2 Carbs for my engine.

A Eldebrock 650 CFM "emissions" carb that I use for smog tests and a Edelbrock 750 that I use between inspections.

The 650 is the one that I set up real lean for the test and it's on the shelf waiting for next year.

The 750 runs a little on the rich side, just were you would want it for street performance.

To: F150 Daniel
My cats have about 7,000 miles on them, and since my hydrocarbons were low, they were working fine. As I found out in researching the problem with high carbon monoxide, the cats reduce hydrocarbons but not CO.

I just needed to set the carb leaner.

Thanks foe all of the comments and help on this post.

Jerry T

 

As far as emissions testing cars older than '97, how can they expect vehicles to pass an emissions test if they were never meant to in the first place? How far back does the testing go? I also live in Tx, in the Austin area. We are going to have to start testing soon. I drive a '66 f100 with an 87 302 and a stock 89 suburban (like all good texans, it is a requirement). This concerns me. They claim they are going to model our program after others in the state. Or is this just another honda lover ploy to get these vehicles off the road?

Scott