Help: Failed CO test in MA 1990 300SE
 

Failed MA Dyno test
Car has been very well maintained.

First Test, Car was cold
Grams Per Mile
Reading Limit
HC 1.66 2.00
CO 56.32 30.00
NOx 1.29 3.00


2nd test car is Fully warm and HOT
Grams Per Mile
Reading Limit
HC 1.39 2.00
CO 33.96 30.00
NOx 1.20 3.00

Oil was replaced about 800 miles ago, plug have about 35K on them
I was thinking of just changing the oil and plugs then trying again.
Any thoughts?
What caused high CO readings? I thought maybe the cats need to be replaced but since the HC is OK than I don't think that will help?
Thanks in advance.

Page down - same subject, same state, same answer.

Duke

Duke2.6 what do you mean by page down? Did not see anything after your post?

Duke meant...
 

...scroll down the threads about 6 or so. Emissions problem for Bruno

That car failed for NOx not CO.

high CO -> mixture problem?
 

Dealing with my problem I found a thread in the archives that might be useful. High CO seems be indicative of a bad mixture adjustment. A starting point might be checking duty cyle to see whether the car is in proper closed loop operation.

http://www.peachparts.com/shopforum/tech-help/57780-300e-failed-smog-check-causes.html?highlight=stuck+egr+valve

Good luck! Bruno

You need to follow the same general troubleshooting proceedure as outlined in the referenced threads, and retarding the ignition map will both lower NOx and HC/CO.

Look at the effect that retarding the igntion map had on all emissions relative to my previous test.

As always, troubleshooting starts with checking the duty cycle and O2 sensor output waveform.

Since there is no easy way to test catalyst efficiency, you test and check EVERTHING else and then retard the timing map if necessary. If this fails change the catalyst as a last resort (since its very expensive) I think a lot of good catalysts are thrown away on a whim without thorough troubleshooting or retarding the timing map. Most shops don't understand the generation and control of emissions and just change parts until it passes, which can end up costing nearly as much as these cars are worth.

Your choice - find a shop (if possible) that knows how to troubleshoot and correct emissions problems, or learn yourself by reading various emission test threads, and downloading all the service information and STUDYING it thoroughly so you understand the how the various emssion control systems/components work.

Duke

Duke2.6
Thanks for the help,
Question is why would I need to adjust the timing or fuel? I know neither one has been adjusted since it rolled off the assy line.
Would bad or worn plugs make the CO higher than normal if CO is an indication of unburned gas?
Thanks

Did you read the discussion of catalyst aging?

Did you read the discussion on the effects of the ignition timing map profile on NOx? Catalyst temperature?

Did you read the discussion of the ignition system, including the use of correct non-resistor plugs and checking igntion wires and cap rotor RFI resistors?

Did you read how the exhaust O2 content is a diagnostic tool? (You did not list O2 content, but the other MA report posted O2 content, so I assume your report lists it, too.)

If nothing ever changed, there would be no need for emissions testing, but components "drift" and catalysts degrade. If the duty cycle has never been checked since the car was built, it should be checked and adjusted, if required. Differences in fuel blends over the years, alone can change the duty cycle due to the addition of oxygenates and slight changes in the C/H ratio.

What I have endeavored to do in my emission discussions is to help all understand how emissions are formed and the effect of various engine operating parameters on both emission creation and control. If you spend the time to read my essays, you should gain insight into the subject and approach trouble-shooting in a rational manner in order to avoid the willy-nilly replacement of componets that could cost hundreds if not thousands of dollars in lieu of finding a possible simple problem or performing some judicious adjustements.

If you're looking for silver bullets - there aren't any.

Duke