What would make engine put out a ton of CO but low hydrocarb

[Guest Anonymous]

Well i took my stock 76 280z with the stock L engine down to the ol' smog check station (i live in cali) and it failed smog miserably. HOWEVER! this was only in one of the 3 categories(carbon monoxide) that it failed(it was a gross polluter). The other two categories(hydrocarbons and something else) passed very low under the margins. What could cause the engine to produce a ton of CO? I have heard that might be running lean or that it needs a new airflow mass sensor and injectors. Any input is welcome!

[Mike kZ]

Didn't California Z's have cataletic converters?

Does yours?

[Owen]

Mine didn't have catalytics and neither does 2 of my friends.

 

Owen

[383 240z]

Well after digging out my old text books I found my notes on five gas theroy and here goes. a very high CO and very low O2,NOx with a mid low CO2,and HC indicates an A/F of about 10:1 you are to LEAN!!! the trick to controlling CO emissions during combustion is to make sure you have the right amount of O2 and fuel in the mix you want enough O2 to form CO2 but not so much that you develop a lean misfire A lean misfire decreases performance and increases HC emissions When the mix is rich the engine produces a lot of CO As the mix passes the stoichiometric (14.7:1) ideal and goes lean When the mix is lean CO levels out and the curve no longer indicates anything CO is only a useful indicator of a rich mix. sorry for the long response but this is a very involved subject Keith

[Guest Anonymous]

hey thanks a lot. The original air cleaner has a stock pipe that inputs air from *inside* the engine compartment. Could this be a problem? The mass air flow sensor controls the flow of air to the intake manifold so logicly that could be the problem. Other than that... Is there any possible way to adjust the air/fuel mixture, and would doing this give a performance gain?

 

And by the way, the car is a california model and it does have a cat i have inspected the exhaust system and it is definately there however rusted. + there is a catalyser temp light on the dash and a fuse for that circut in the box.

[Guest Anonymous]

I am solving this problem piece by piece: if any one is interested in my progress, eyeball my other topic in "Troubleshooting"

[Pop N Wood]

Want to second what 383 said. I have a carbureted 1970 240 that had to be CA smogged. I use to think I could lower the overall emissions by leaning out the SU’s prior to the test. The other numbers did go down, but then it failed the CO part. After a couple of tries I found the emissions were lowest when the engine was tuned to run the best.

 

Who’d a thunk? Just keep a well tuned engine and the emissions should take care of themselves.

 

Don’t have any experience with a 76 Z, I assume it is fuel injected. But I would say doing a complete tune up before the test is the first place to start. Pay attention to anything that could cause a lean condition (such as vacuum leaks, bad O2 sensor etc). Mine also had trouble with worn throttle shaft bushings causing a lean condition at idle. Figured this out by squirting starting fluid around the bushing while watching for a change in idle speed.

 

One thing that did help me was replacing the smog pump (maybe not a solution for everyone since mine went totally bad). Pump enough clean air into the exhaust and all of the percentages will drop. As a guy working in a nuke plant once told me, “The solution to pollution is dilution.â€

[Brad-ManQ45]

I beleive the 10:1 ratio in one of the responses idincated a RICH condition - 10 parts air to 1 part fuel.

 

14.6 - stoichiometric is 14.6 parts air to 1 part fuel. This is for gasoline w/o oxygenates.

 

Lean would be MORE parts air to 1 part fuel....