PeachParts Mercedes-Benz Forum - 89 260E Fails CA Smog Test

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You might be running a little on the lean side if you are getting high NOx. Check the basic A/F mixture and try tweaking it back to stochiometric (50% duty cycle) if its lean.

In searching through various discussions in this forum I did find this interesting quote from Stevebfl, which addresses my now-very-low CO%, which is certainly below the 0.2% CO referred to in Steve's post, quoted below.

Quote:

Originally Posted by stevebfl (Post 321077)

In the last test I mentioned, the concept is to run the car and evaluate the mixture by seeing how it affects the O2 sensor voltage. The sensor is a 0 to 1v voltage generator. It creats voltage that is related to engine mixture within a small range.

Its very likely that the sensor is fouled, but the way to tell is to run the motor (the sensor has to get hot which requires time and engine speed - don't be in a hurry), while monitoring the voltage (sensor on its own not connected). As I stated its likely to be either 1v or zero volts. If its one volt and its working then the mixture is greater than 1% CO (if measured before cat with an exhaust gas analyser - which you really can't do anyway). Here is why I suggested to do the 12v thru Cap'n mixture change. This will lean the car out and unless your are very rich it will bring the mixture through the range 0-0v - 1.0v. if not you can lean it out till it does.

Remember a proper working O2 sensor measures mixture from 0% CO to 1% CO. This is a very small range. The car will start running poorly above 6% CO and below 0.2% CO (maybe higher). The car will be held to mixtures in the range of .3% CO to .7% CO by a functioning system and it can only correct a rich car running less than 4% CO.

If everything is functioning you will be able to lean out the mixture till the O2 sensor just drops from around 1v. Then you will be able to reconnect the wire and the system will correct mixtures less than .5v by adding fuel (within the 10ma correction range we have already tested) till the mixture becomes richer than .5v at which time the current will reverse and the system lean out till it switches the other way. Once the O2 sensor is hot and everything is adjusted then the .3v to .7v O2 sensor swings will be kept in check by about a 4ma total mixture correction.

If this were a training course this would really be a short story. If you don't understand ask me again.

Looks like the catalyst isn't working to reduce NOx

Quote:

Originally Posted by M.B.DOC (Post 2260931)

Looks like the catalyst isn't working to reduce NOx

I just replaced the rear cat with a Magnaflow aftermarket cat ( it is NOT a 3-way).... did I just make a horrible stupid mistake?

Or, should I be focused on replacing the two pre-cats connected to the manifold?

I also conducted further testing this weekend on the EHA, O2 Sensor, ICV & Duty Cycle and posted all of my procedures (per an old Stevebfl thread) and results at:

http://www.peachparts.com/shopforum/showthread.php?t=258180

If you are getting a duty cycle reading, then the O2 sensor and computer are "working".

Quote:

Originally Posted by M.B.DOC (Post 2261001)

If you are getting a duty cycle reading, then the O2 sensor and computer are "working".

Yup, certainly seems like my Jetronic system is functioning properly... And from all my reading it appears that all my emission figures are very good EXCEPT for NOx. Latest emissions results (CO has gotten very low):

MPH=15 RPM=1520 %CO2=15.0 %O2=0.1 HC(PPM)=53 CO(%)=.03 NOx(PPM) =1508 FAIL
MPH=25 RPM=1793 %CO2=15.1 %O2=0.0 HC(PPM)=44 CO(%)=.06 NOx(PPM)=1156 FAIL

So, if I am now faced with replacing the Catalytic Converter system, does this mean replacing:

just the rear Cat with another 3-way system?
just the rear Cat with any aftermarket Cat? (which I've already done :( )
just the two front pre-Cats?
all three Cats with an OEM replacements?
or some other solution?

At one point in time California made car owners add EGR system to reduce NOx.

I would think the OE system is the only way to not see the emission man all of the time.

Your diligence is commendable, and I sent you an email through this site, but you didn't respond. (You should verify that you have a current email address registered on this site.)

All 02 sensor emission systems require a three-way catalyst to control NOx as does your Mercedes. If the replacement catalyst is really just a "two-way" type, that is the likely cause of your high NOx. I doubt if you needed a new catalyst, but it's too late now unless you saved the original.

You might be able to squeak by with easy timing map modifications that I have outlined in the past and you have apparently found in the archives.

I am willing to discuss your situation and help you out privately, but I no longer regularly post to this discussion board.

Duke